Iron Ore Technical Working Group
Submission for Evaluation and
Verification
MARINE REPORT
April 2013
All participants of the TWG operate under international and their respective national
antitrust laws and regulations. Suitable controls are in place to ensure all meetings are
minuted and discussions and material exchanged do not transgress antitrust
requirements. All participants of the Technical Working Group have access to in-house
competition law advice, operate at all times under all applicable international and national
competition laws and regulations and have been cautioned accordingly.
Preamble
At the 17th session of the Sub-committee on Dangerous Goods, Solid Cargoes and Containers,
Member States directed the Correspondence Group (CG) on the transportation of the iron ore fines
(established at DSC 16) to continue its work with updated Terms of Reference to:
.1) consider the adequacy of current methods for determining transportable moisture limit
(TML) for iron ore fines and consider new and/or amended existing methods to be included in
appendix 2 of the IMSBC Code – to be completed by end of May 2013 (DSC 17/4/34 and
DSC 17/INF.9);
.2) consider the evaluated and verified research into Iron Ore Fines – to be completed by end
of May 2013;
.3) prepare draft individual schedule(s) for iron ore fines and any required amendments to
appendix 2, taking into account .1 and .2 above and review the existing iron ore schedule, as
necessary; and
.4) submit a report to DSC 18.
In an effort to ensure the CG’s deliberations are informed by the latest scientific insights, the three
largest iron ore producers (with the support of their respective Competent Authorities) committed to
form an Iron Ore Technical Working Group (TWG). The TWG is coordinating research efforts into the
transportation of iron ore fines to provide independently “evaluated and verified” findings that can
serve as the basis for decision making.
To this end, the TWG will produce the following reports:
•
•
•
•
•
Date 9-Feb-16
Report #1: “Terms of Reference .1” – This report assesses the adequacy of current IMSBC
Code methods for determining the Transportable Moisture Limit (TML) of Iron Ore Fines
(IOF).
Report #2: “Marine Studies” – This document reports the characteristics of vessel motions
and forces imposed on IOF cargoes during transit; the impacts of vessel size and sea
conditions (swell, sea and wind); and, the stability of vessels in various cargo behaviour
scenarios.
Report #3: “Routine Test Method”– Building on the outcomes of Report #1, this document
explores potential adjustments to one of the existing routine IOF test methods – or a new
test – to better reflect actual in-hold shipping conditions and observations.
Report #4: Reference Tests – This report provides further evidence to substantiate the
applicability of the routine IOF test method identified in Report #3 through the material’s
performance in real-world conditions using a variety of well-established geotechnical
methods, numerical modelling and cargo observation.
Report #5: Final Submission – This report will integrate the results of all of the preceding
research into a series of recommendations that can inform the deliberations of the
Correspondence Group.
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The TWG have appointed external experts (Prof Kenji Ishihara, Prof Junichi Koseki and Dr Kourosh
Koushan) in the relevant disciplines to verify each of the reports. This evaluation is followed by an
independent scientific review process undertaken by Imperial College of London (Dr Stephen
Neethling, Professor Dracos Vassalos and Professor Velisa Vesovic), under the direction of the
International Group of P&I Clubs (IG). IG represents a group of industry NGOs that includes BIMCO,
Intercargo, International Chamber of Shipping and IFAN. The finalized reports are then submitted to
the CG, fulfilling the requirement for “evaluated and verified” research.
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Executive Summary
The Technical Working Group (TWG), comprising one Brazilian and two Australian mining companies,
has undertaken marine studies to identify and quantify the inertial forces that vessels of different sizes
and their cargoes experience during ocean voyages. A working knowledge of these vessel forces is
required to supplement knowledge on the behaviour of bulk cargoes such as iron ore fines (IOF)
during transit.
This Marine Report is not a study of liquefaction. The Marine Report defines the input parameters that
allow laboratory testing and cargo modelling to be undertaken and will be outlined in Report 4:
Reference Tests.
The parameters determined in this Marine Report include vessel size, the extent of cargo movement,
vessel accelerations (at various positions on a vessel), sea states (period, frequency and modal
behaviour), vessel responses (roll, pitch, yaw, heave, sway and surge) and loss of intact stability;
forming modelling inputs that can be referred to as cyclical stresses/forces that may be required for
liquefaction. In addition to measurements during voyages, vessel motions and forces were determined
from voyage simulations over the lifetime of vessels travelling on three major iron ore routes. The
simulations included severe sea states as well as tropical revolving storms.
The Marine Report excludes, apart from Cargo Observations, the other key liquefaction parameters
such as material/mineralogical properties, pore water pressure, details of wet base formation, free
surface water (where applicable). All of the above aspects are considered in Report 4.
The research undertaken covered Capesize, Handymax and Handysize vessel types. Capesize
vessels were the principal focus of this study; this vessel-type carries 91.5 per cent of global iron ore
tonnage. In addition, Handysize and Handymax vessels were included in the research, although these
carry less than two per cent of total IOF tonnage. The findings determined from this report are carried
forward to future work.
Key Research Findings
Vessel Motions and Forces
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Contribution from vibrations associated with engines are negligible.
In respect of rigid body motions, based on vessel motions captured and calculated, only the
vertical and the transverse motions are significant compared to longitudinal motion.
For vertical and transverse motions, accelerations in Handysize vessels are up to twice those
of Capesize vessels.
Capesize vessels have a natural roll period of 10 seconds or 0.1 Hz (based on various RAOs
and response spectra).
Hold 1 (forward hold) experiences the largest accelerations.
Real-world accelerations measured during voyages are typically lower than those predicted by
voyage calculations.
The observed vessel accelerations are less than 1G, typically 0.1G.
Weather routing as an outcome of good seamanship reduces the maximum accelerations
experienced.
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Vessel Stability
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For Capesize vessels, stability is not compromised unless more than 50% of the cargo mass
has moved significantly
Handymax and Handysize vessels have a lower reserve stability than Capesize when carrying
heavy density cargoes.
Capesize vessels typically have a metacentric height (GM) many times the value required by
the IMO Rules and the areas under the righting lever curve are typically10 times the rule
requirements
Cargo Observations
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Laser scans show quantitatively that the IOF cargo mass did not move significantly within a
hold during the voyages undertaken.
Cargo volume compaction varies from 0-10%, but is typically around 1-2%.
Laser scanning/survey allows for precise determination (+/-0.5% volumetric) of cargo bulk
density.
Volumes of pumped bilge water indicate up to 1% moisture reduction (absolute percent
change) during a voyage for Brazilian cargoes. The moisture reduction for Australian iron ores
is at least an order of magnitude less.
Bilge pumping data as well as discharge inspections and observations show Australian iron
ores fines have no appearance of free water at discharge. Some Brazilian ores do show the
appearance of free water during the voyage but can be managed by the pumping of bilges.
Limiting trimming to the natural angle of repose impedes the surface impacts of free water.
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Table of Contents
1
INTRODUCTION ............................................................................................................................ 17
2
VESSEL MOTION AND FORCES ................................................................................................. 18
2.1
CALCULATED VESSEL MOTIONS AND FORCES ............................................................................. 18
2.1.1
Introduction and methods ................................................................................................ 18
2.1.1.1 Australia - A .................................................................................................................. 18
2.1.1.2 Australia - B .................................................................................................................. 25
2.1.1.3 Brazil ............................................................................................................................ 28
2.1.2
Results ............................................................................................................................. 31
2.1.2.1 Australia - A .................................................................................................................. 31
2.1.2.2 Australia - B .................................................................................................................. 34
2.1.2.3 Brazil ............................................................................................................................ 36
2.2
MEASURED VESSEL MOTIONS AND FORCES................................................................................ 37
2.2.1
Introduction and methods ................................................................................................ 37
2.2.1.1 Australia - A .................................................................................................................. 37
2.2.1.2 Australia - B .................................................................................................................. 39
2.2.1.3 Brazil ............................................................................................................................ 41
2.2.2
Results ............................................................................................................................. 42
2.2.2.1 Australia - A .................................................................................................................. 42
2.2.2.2 Australia - B .................................................................................................................. 48
2.2.2.3 Brazil ............................................................................................................................ 53
2.3
COMPARISON AND FINDINGS ...................................................................................................... 62
3
VESSEL STABILITY...................................................................................................................... 64
3.1
INTRODUCTION .......................................................................................................................... 64
3.2
METHODOLOGY ......................................................................................................................... 64
3.2.1
Stability analysis .............................................................................................................. 64
3.2.1.1 Free surface ................................................................................................................. 64
3.2.1.2 Cargo shift .................................................................................................................... 67
3.2.2
Rule compliance .............................................................................................................. 67
3.2.3
Ship survivability .............................................................................................................. 68
3.3
RESULTS .................................................................................................................................. 69
3.3.1
Typical Capesize Vessel .................................................................................................. 69
3.3.1.1 Stability analysis ........................................................................................................... 70
3.3.1.2 Rule compliance ........................................................................................................... 72
3.3.1.3 Ship survivability .......................................................................................................... 74
3.3.2
Typical Handymax Vessel ............................................................................................... 75
3.3.2.1 Stability analysis ........................................................................................................... 75
3.3.2.2 Ship survivability .......................................................................................................... 78
3.3.3
Typical Handysize Vessel ................................................................................................ 78
3.4
COMPARISONS AND FINDINGS .................................................................................................... 79
4
CARGO OBSERVATIONS ............................................................................................................ 81
4.1
AUSTRALIA - A OBSERVATIONS ................................................................................................... 81
4.1.1
Introduction and Methods ................................................................................................ 81
4.1.2
Results ............................................................................................................................. 84
4.2
AUSTRALIA - B OBSERVATIONS ................................................................................................... 87
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4.2.1
Qualitative Cargo Movement Measurements .................................................................. 88
4.2.2
Quantitative Cargo Movement Measurements ................................................................ 88
4.2.3
Bilge Checks .................................................................................................................... 93
4.2.4
Vessel Journey Reports ................................................................................................... 94
4.2.5
Discharge Superintending ............................................................................................... 95
4.3
BRAZIL OBSERVATIONS ............................................................................................................. 96
4.3.1
Laser Scanning ................................................................................................................ 96
4.3.2
Free water ........................................................................................................................ 97
4.3.3
Bilge Data ........................................................................................................................ 98
4.3.4
Cargo Trimming Practice ................................................................................................. 99
4.4
COMPARISON AND FINDINGS .................................................................................................... 100
5
CONCLUSIONS AND RECOMMENDATIONS ........................................................................... 101
6
REFERENCES ............................................................................................................................. 103
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List of Figures
Figure 1: World iron ore carrying vessel mix by % total Iron Ore tonnage ............................................ 17
Figure 2: World iron ore carrying vessel mix by % total Iron Ore voyages ........................................... 18
Figure 3: GWS climatological areas ...................................................................................................... 19
Figure 4: Wave scatter diagram for area 41, East China Sea ............................................................... 20
Figure 5: Operability plot ....................................................................................................................... 21
Figure 6: Australia – China .................................................................................................................... 22
Figure 7: Brazil – China ......................................................................................................................... 22
Figure 8: Guinea – China ...................................................................................................................... 22
Figure 9: TRS seasons .......................................................................................................................... 23
Figure 10: Significant wave height for Australia-China route ................................................................ 24
Figure 11: Distribution of SDA values ................................................................................................... 24
Figure 12: Ocean world map with 95% confidence significant wave height (Hs) .................................. 25
Figure 13: Typical Australia B iron ore voyages Port Hedland to China, Port Hedland to Port Kembla 25
Figure 14: General arrangements of Capesize and two Handysize vessels ........................................ 26
Figure 15: Examples of hull diagrams ................................................................................................... 27
Figure 16: Loading condition for modelled vessels (Cape, 19 kDWT Handy, 13 kDWT Handy) .......... 27
Figure 17: Orcaflex output showing vessel animation ........................................................................... 28
Figure 18: Voyage route Brazil to China ............................................................................................... 29
Figure 19 : 180 kDWT Capesize bulk carrier ........................................................................................ 30
Figure 20: Capesize midship section .................................................................................................... 30
Figure 21: Summary of mean conditions and vessel behaviour ........................................................... 31
Figure 22: Mean, most probable voyage and 1% extreme SDA values ............................................... 32
Figure 23: Wave heading convention .................................................................................................... 34
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Figure 24: Effect of wave direction on vessel roll .................................................................................. 34
Figure 25: Effect of wave direction on vessel pitch ............................................................................... 34
Figure 26: Calculated vessel accelerations at hold 1 (double amplitude) ............................................. 35
Figure 27: Capesize vessel, vertical accelerations at hold 1, in DNV zone 100 sea state ................... 35
Figure 28: Comparison of the maximum vertical accelerations for Capesize and Handysize vessels in
the same sea state (double amplitude) .................................................................................. 35
Figure 29: Phase angles between heave and sway accelerations for vessel in bow quartering seas . 37
Figure 30: Sensor arrangement ............................................................................................................ 38
Figure 31: Accelerometer assemblies at each hold ............................................................................. 38
Figure 32: Vessel motion instrumentation (a) main cabinet, (b) instrument cabinet with gyro &
accelerometer ........................................................................................................................ 39
Figure 33: Capesize C instrument locations.......................................................................................... 40
Figure 34: Location of vessel monitoring instruments ........................................................................... 42
Figure 35: Significant double amplitudes all sensors ........................................................................... 43
Figure 36: Voyage #1 track overview .................................................................................................... 44
Figure 37: Example acceleration spectra .............................................................................................. 45
Figure 38: Motion data event 4, voyage 1 - loaded ............................................................................... 46
Figure 39: Measured acceleration spectra event 4, voyage 1 - loaded ................................................ 46
Figure 40: Motion data event 8, voyage 2 - loaded ............................................................................... 47
Figure 41: Measured accelerations event 8, voyage 2 – loaded .......................................................... 47
Figure 42: Recorded vessel motion routes ............................................................................................ 48
Figure 43: Magnitude of vertical accelerations by hold in a Capesize vessel ....................................... 48
Figure 44: Vertical accelerations from measured vessel motions (double amplitude) .......................... 49
Figure 45: Measured vessel roll ............................................................................................................ 49
Figure 46: Simplified schematic of vertical hull flexing .......................................................................... 50
Figure 47: Horizontal hull flexure ........................................................................................................... 50
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Figure 48: First mode torsional hull flexure ........................................................................................... 51
Figure 49: Wave radar wave height and direction ................................................................................. 51
Figure 50: Vibration sensor locations .................................................................................................... 52
Figure 51: Average (single amplitude) vibration accelerations in X(longitudinal / surge), Y(transverse /
sway), Z(vertical / heave) axes .............................................................................................. 52
Figure 52: Vertical accelerations at the base of hold 4 (ore loaded on top of sensor) .......................... 53
Figure 53: Position of vessel during voyage.......................................................................................... 54
Figure 54: Roll and pitch motions on hourly basis ................................................................................ 54
Figure 55: Sway and heave motions on hourly basis ............................................................................ 55
Figure 56: Roll and pitch motions on second basis ............................................................................... 55
Figure 57: Heave and sway motions on second basis .......................................................................... 56
Figure 58: Roll response ....................................................................................................................... 56
Figure 59: Pitch response...................................................................................................................... 57
Figure 60: Heave response ................................................................................................................... 57
Figure 61: Cargo hold 5 acceleration time series .................................................................................. 58
Figure 62: Cargo hold 5 acceleration spectra ....................................................................................... 58
Figure 63: Cargo hold 1 acceleration time series .................................................................................. 59
Figure 64: Cargo hold 1 acceleration spectra ....................................................................................... 59
Figure 65: Bosun’s store acceleration time series................................................................................. 60
Figure 66: Bosun’s store acceleration spectra ...................................................................................... 60
Figure 67: Springing vibration spectra ................................................................................................... 61
Figure 68: Main hull girder response spectrum ..................................................................................... 61
Figure 69: Accelerations along ship length. ACCN SD is Acceleration Standard Deviation ................. 62
Figure 70: Capesize vessel roll angle and shift of cargo ....................................................................... 65
Figure 71: 19,000 t Handy size vessel roll angle and shift of cargo ...................................................... 66
Figure 72: 19,000 t Handy size vessel roll angle and shift of cargo ...................................................... 66
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Figure 73: Severe wind and rolling ........................................................................................................ 67
Figure 74: Typical Capesize vessel used in the stability analysis ......................................................... 69
Figure 75: Typical homogeneous load condition in a Capesize vessel ................................................ 70
Figure 76: Righting lever with full free surface in all holds .................................................................... 71
Figure 77: Righting lever and listing curve for typical Capesize 10o cargo shift condition .................... 71
Figure 78: Reserve stability in Capesize vessel .................................................................................... 72
Figure 79: Effect of cargo failure in increasing numbers of holds and shows the angle of loll ............. 73
Figure 80: Righting lever curves for Capesize vessel ........................................................................... 74
Figure 81: Righting lever and listing curve for typical Handymax cargo shift condition ........................ 76
Figure 82: Righting lever curve for Handymax suffering further cargo shift .......................................... 77
Figure 83: Righting lever curve for a combination of free surface and cargo shift ................................ 78
Figure 84: Cargo observed (a) after loading and (b) before discharge ................................................. 81
Figure 85: Photos showing cargo hold conditions at end of discharge ................................................. 82
Figure 86: location of laser scanner and inverted tripod (inset) ............................................................ 83
Figure 87: Laser scanner profile of cargo surface ................................................................................. 84
Figure 88: Laser scan of empty hold ..................................................................................................... 85
Figure 89: Laser scan of hold containing cargo .................................................................................... 86
Figure 90: Cross section of cargo after loading and before discharge ................................................. 86
Figure 91: Capesize C: instrumenting an empty hold ........................................................................... 87
Figure 92: Capesize vessel hold marking start (left) and end (right) of voyage .................................... 88
Figure 93: Capesize vessel cargo laser scanning survey ..................................................................... 89
Figure 94: Raw laser scan images from only one instrument setup point ............................................ 89
Figure 95: Capesize vessel cargo survey Hold 1 contours at loading (left) and discharge (right) ........ 90
Figure 96: Cargo surface difference contour map for hold 1 of a Capesize vessel .............................. 90
Figure 97: Capesize journey and key motions heave, pitch, roll translated to vertical acceleration ..... 91
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Figure 98: Capesize vessel surface change profile due to journey shown in Figure 97 ....................... 91
Figure 99: Volume difference due to 14 day voyage ............................................................................. 92
Figure 100: Bulk Density Change due to 14 day voyage ...................................................................... 93
Figure 101: Bilge pumping records show little if any free moisture ....................................................... 93
Figure 102: Vessel behaviour in extreme weather ................................................................................ 94
Figure 103: Example discharge inspection report extract ..................................................................... 95
Figure 104: Cargo discharge, note dry floor .......................................................................................... 96
Figure 105: Brazilian cargo laser scan .................................................................................................. 97
Figure 106: Material in hold of Capesize bulk carrier before and after voyage ..................................... 97
Figure 107: Laser scan of cargo stow at the end of the voyage ........................................................... 98
Figure 108: Daily amount of water pumped from the bilges for materials 'A' and 'B' ............................ 99
Figure 109: Effect of cargo trimming on ship free surface .................................................................... 99
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List of Tables
Table 1: Significant wave height for Brazil to China Voyage ................................................................. 29
Table 2: Summary of route, conditions and vessel behaviour per m Hs ............................................... 31
Table 3: Maximum encountered SDA values for 300 voyages ............................................................. 33
Table 4: Single amplitude standard deviation of different response in different area along route (bow
quartering, 5% exceedance of incident waves) ..................................................................... 36
Table 5: Description of responses ......................................................................................................... 36
Table 6: Vessel iHeave deployments .................................................................................................... 39
Table 7: iHeave installed positions and voyage data ............................................................................ 40
Table 8: GPS Positioning Specification ................................................................................................. 40
Table 9: Ship data and sea state record ............................................................................................... 53
Table 10: Summary of vertical and transverse accelerations experienced by Capesize, Handymax,
and Handysize vessels .......................................................................................................... 63
Table 11: Typical Capesize vessel details ............................................................................................ 69
Table 12: Typical Capesize vessel free surface correction ................................................................... 70
Table 13: Effect on vessel compliance with increasing number of holds affected ................................ 73
Table 14: Capesize vessel GM due to cargo shift by number of holds ................................................. 74
Table 15: Effect on vessel survivability with increasing number of holds affected ................................ 75
Table 16: Typical Handymax vessel details .......................................................................................... 75
Table 17: Typical Handymax vessel free surface correction ................................................................. 76
Table 18: Typical Handymax survival conditions .................................................................................. 78
Table 19: 19 kDWT Handysize vessel GM due to cargo shift by number of holds ............................... 79
Table 20: 13 kDWT Handysize vessel GM due to cargo shift by number of holds ............................... 79
Table 21: Bilge pumping summary ........................................................................................................ 83
Table 22: Cargo compaction from cargo height measurements ........................................................... 85
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Table 23: Bilge water volumes and percent cargo moisture reduction ................................................. 85
Table 24: Laser scanning summary of all hold results for cargo compaction and bulk density ............ 87
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Abbreviations
AQWA
Frequency domain diffraction analysis program
BF
Beaufort Number
BMT
British Marine Technology
CT
Cyclic Triaxial test
DGPS
Differential Global Positioning System
DNV
Det Norske Veritas
DWT
Dead Weight Tonne
FEM
Finite Element Method
FP
Forward Perpendicular
G
Acceleration due to Gravity
GM
Measurement of positive metacentric height
GNSS
Global Navigation Satellite System
GPS
Global Positioning System
GWS
Global Wave Statistics
GZ
Curves of statistical stability
Hs
Significant Wave Height, the mean wave height (trough to crest) of the
highest third of the waves (H1/3).
Hz
Hertz
I/O
Input/Output
IMO
International Maritime Organisation
IMU
Inertial Measurement Unit
IOF
Iron ore fines
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IS Code
Intact Stability Code which defines the regulations for vessel stability by
the IMO
ISSC
Also known as the Pierson-Moskowiz spectrum and defines the
relationship between energy and frequency in the ocean
LCB
Longitudinal Center of Buoyancy of a vessel
LCF
Longitudinal Center of Floatation of a vessel
LOA
Length Overall
MRU
Motion Response Unit
NAPA
Ship stability software
NSW
New South Wales
QTF
Quadratic Transfer Function
RAO
Response Amplitude Operator (RAO) is an engineering statistic, or set of
such statistics, that are used to determine the likely behaviour of a ship
when operating at sea.
RMS
Root Mean Square
SA
South Australia
SDA
Significant Double Amplitude, mean of the highest third values
TML
Transportable Moisture Limit
Tp
Peak Period
TRS
Tropical Revolving Storm
TWG
Technical Working Group
Tz
Zero Up Crossing Wave Period
VCG
Vertical Centre of Gravity
VPR
Vessel Performance Report
WA
Western Australia
X, Y, Z
Direction of acceleration or force where X is longitudinal (horizontal,
surge), Y is transverse ( horizontal, sway), and Z is vertical (heave)
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1
INTRODUCTION
Understanding the behaviour of iron ore fines (IOF) cargoes during ocean transportation requires
knowledge of the actual forces to which the vessel is subjected during a voyage and the consequent
behaviour of the vessel. Measurements of these forces are not readily available and or well
documented. This study, entitled the Marine Report, aims to identify and quantify such forces for
different sized vessels. The behaviour of vessels during voyages has been characterised by
calculating and measuring vessel motions and vibrations in a range of sea states.
This study outlines the methodology and results of research undertaken by two Australian and one
Brazilian mining companies collaborating as a Technical Working Group (TWG). The research
includes vessel motion characterisations, voyage simulations and instrumentation of vessels for
determining the inertia loads that are imposed on the cargo during transit, due to ship motions in
waves, engine vibrations and propeller excitation. By understanding and describing the motion and
vibrations experienced by the vessel – ultimately affecting the behaviour of the cargo – across the
possible range of sea conditions encountered. This information constitutes critical input for
establishing the force conditions required for laboratory scale testing and boundary conditions for
numerical modelling can be determined.
The Marine Report also investigates the stability of different vessel types, in given cargo movement
scenarios, to determine the ability of vessels to maintain positive stability even when cargo shifts
occur.
Finally, the study presents cargo observations conducted by each of the TWG members, to describe
the actual behaviour of the cargo during a voyage.
IOF cargoes are predominantly transported across oceans in Capesize vessels, either Bulk Carriers or
dedicated Ore Carriers typically 150 kDWT or more. In 2012, 91.5% of IOF tonnage was carried by
Capesize vessels and 4% carried in Panamax class vessels. The smaller vessels in the Handymax
(~50 kDWT) and Handysize (> 20 kDWT) classes carry less than 2% of the world tonnage of iron ore
(Figure 1). As a percentage of the total voyages occurring during 2012, Capesize vessel accounted for
~80%, Panamax class vessels (including mini Cape) account for about 14% and the small vessels,
Handymax and Handysize making up about 6% (Figure 2).
Figure 1: World iron ore carrying vessel mix by % total Iron Ore tonnage
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0.5 1.7 1.4
2.6
8.7
3.2
2.0
Capesize 175kDWT
Mini Capesize 105kDWT
Post Panamax 80kDWT
Panamax 65kDWT
Large Handymax 45kDWT
Handymax 40kDWT
Large Handysize 25kDWT
Handysize 18kDWT
79.8
Figure 2: World iron ore carrying vessel mix by % total Iron Ore voyages
As the largest proportion of the iron ore carrying fleet are Capesize vessels, these vessels have been
the focus of much of this study. Handymax and Handysize vessels, however, have also been studied,
as these vessel types are the only ones implicated in actual losses at sea while carrying IOF.
2
VESSEL MOTION AND FORCES
Findings on the characteristics of vessel motions and forces were obtained through voyage
simulations (Section 2.1) and observations of the actual forces experienced by instrumented ships
(Section 2.2). The findings allow for the determination of the possible inertia loads imposed on the
cargo during transit and the impacts of vessel size and sea conditions (swell, sea and wind).
2.1
Calculated Vessel Motions and Forces
2.1.1
Introduction and methods
Vessel rigid body motions were estimated using vessels’ Response Amplitude Operators (RAOs)
calculated via hull strip theory, which was determined by utilising general arrangement drawings, lines
plans, mass distribution, stiffness and damping coefficients derived from information provided by the
shipbuilder or Class society. The following sections outline the approaches used by each TWG
member.
2.1.1.1
Australia - A
In the offshore industry, the availability of wave measurements has led to the introduction of scatter
diagrams (
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Figure 3), reflecting the joint statistics of significant wave height and average zero-upcrossing period.
Work by BMT (Hogben et al., 1986; and BMT, 1986) has provided a practical basis for the design of
ships.
Figure 3: GWS climatological areas
Figure 4 shows typical wave statistics for Area 41, the East China Sea, which was used together with
Area 90 (SE of South Africa) in this study.
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Figure 4: Wave scatter diagram for area 41, East China Sea
Rigid body motions were estimated using Strip-Theory in voyage simulations and conventional panel
code for longitudinal bending moments and local pressures below the keel for added resistance and
speed loss was estimated using Rankine source method and an empirical estimate of available thrust.
Longitudinal bending deflection was determined via quasi-static amidship bending moment and
whipping via an empirical estimate on basis of Storhaugh’s tests (Storhaugh, 2007). These
estimations along with the wave scatter diagrams are used to determine operability plots. As an
example, a given ship in the southern Indian Ocean, the operability plot can be determined as shown
in Figure 5. The lines in the plots indicate the highest speed that can be maintained up to a particular
wave height. The total speed loss is the result of the added resistance in waves, which is revealed by
the “dip” in speed in longer waves and the wind, which is higher in short waves.
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Figure 5: Operability plot
In Figure 5 the ship loses around 1 knot in about 2 m waves (~BF5). This increases to around 6 knots
in 6.5 m waves (~BF9).The results for all ships show that the sustained speed is quite low in higher
waves. This implies that the estimates of the motions and accelerations, which were made at 14 knots,
are probably rather conservative.
The SAFETRANS package (DNV approved in 2007) was used to make some 300 trips with a
Handymax (~50 kDWT) vessel and a 205 kDWT Capesize vessel on three routes, from North-West
Australia, Brazil South America, from African Guinea into China. The routes are shown in Figure 6 Figure 8.
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Figure 6: Australia – China
Figure 7: Brazil – China
Figure 8: Guinea – China
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The individual trips start at random points in the SafeTrans 10-year database with wind, waves and
swell and the related forecasts. At every 3-hour time step the prevailing conditions are used to
establish the progress. The 300 voyages simulated cover the lifetime of the ship if the ballast return
voyage is counted as well (i.e. ~70 year for the long routes, ~30 year for the short route Australia to
China).
The ship routes from Australia to China are affected predominantly by Tropical Revolving Storm (TRS)
occurrence in the South China Sea in the period April-November. Some TRS occurrence is present in
the Timor Sea and offshore North West Australia, but to a much lower intensity in the period
December-April.
For the route Brazil or Guinea to China, the South Atlantic is free of TRSs, and the Indian Ocean south
of 40 0 S latitude is out of TRSs as well. The route, as shown in the Figure 9, is laid between the TRS
areas of Indian Ocean and NW Australia, so in the TRS season for those basins, stretching from
December to March (with extensions to October and April), occurrence of severe TRSs over the route
is scarce. Hence, also for the Brazil-China routes the TRS season in the South China Sea is
dominant.
Figure 9: TRS seasons
It is to be noted that outside the TRS season, sea states are dominated by normal storm weather,
which is present in the higher latitudes of the Indian Ocean and in the South China Sea. The areas at
lower latitude are tropical, and have usually mild weather.
Every step in the simulation yields information on the “significant double amplitude” or SDA
(approximately the maximum single amplitude in a three-hour record) and mean period of the
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encountered wave and the ship behaviour. The roll and pitch and the vertical and transverse
accelerations were evaluated.
Figure 10 below shows an example of the encountered significant wave height on the Australia-China
route. The mean wave height is around 1.6 m.
Figure 10: Significant wave height for Australia-China route
Sorting the SDA values and plotting them as a function of the “frequency of exceedance” (the fraction
of the three-hourly SDA values exceeding a particular level) yields the “cumulative” distributions of the
SDA’s. Figure 11 below illustrates the distributions of the wave height, the roll angles and the vertical
and transverse accelerations at Station 16 (Hold 1) for the above route.
Distributions SDA's
Freq.of Exc. [1/3hr time step]
1
0.1
0.01
110
3
110
4
110
5
0
5
10
15
20
25
SDA
Sign.Wave Height [m]
SDA Roll [deg]
SDA Vert.Acc.St.16 [m/s2]
SDA Tr.Acc.St.16 at z-COG [m/s2]
Figure 11: Distribution of SDA values
A typical trip between Australia and China lasts 135 three-hour time steps (17 days). Reading the
above distribution at F=1/135=7E-3 in the above graph yields a “most probable” (typical) extreme
significant wave height of around 5 m. Of course the largest extreme SDA values that were
encountered over all 247 trips are higher than the typical ones. Reading at the tail at n=33300 or F=
3E-5 yields a significant wave height of around 10 m. This value reflects the typical highest value in
247 trips (4162 days sailing in loaded condition on a China bound leg).
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2.1.1.2
Australia - B
The effect of sea conditions on vessel motion was estimated using a joint distribution of significant
wave height and period (Figure 12) as given in DNV-RP-C205. DNV-RP-C205 specifies long term
distribution parameters for various ocean zones. Based on typical Australia B iron ore voyages Port
Hedland to China, Port Hedland to Port Kembla (Figure 13) and one of the most extreme zone in the
standard sea state distributions were developed for 80%, 95% and 99% confidence intervals (20%,
5% and 1% exceedence levels). In order to model these wave characteristics in Orcaflex, a wave
spectrum approximately representing the relevant sea state was selected. The ISSC spectrum or a
modified Pierson-Moskowiz spectrum was chosen as this represents a fully developed sea in the open
ocean. A range of wave directions were considered for evaluating the resulting vessel motions.
Figure 12: Ocean world map with 95% confidence significant wave height (Hs)
Figure 13: Typical Australia B iron ore voyages Port Hedland to China, Port Hedland to Port
Kembla
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A Cape and two different configuration Handy vessels were modelled. Hull models for each vessel
were developed from general arrangement drawings (Figure 14), lines plans and stability book data
(Figure 15).
.
Figure 14: General arrangements of Capesize and two Handysize vessels
The vessel hull, cargo holds and tanks have been modelled in the ship stability software NAPA. The
resultant hydrostatics have been verified against the stability booklet and were found to be within 0.5%
with respect to displacement, LCF and LCB values. The volume and centre of gravity of cargo holds
were also verified against the stability booklet and were within 1.0%.
The loading condition presented in the vessel’s stability booklet (which is representative of
homogeneous hold iron ore loading) has been used for the analysis. The vessel is loaded to the
scantling draft in this loading condition as shown in Figure 16.
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Figure 15: Examples of hull diagrams
Figure 16: Loading condition for modelled vessels (Cape, 19 kDWT Handy, 13 kDWT Handy)
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The vessel motion RAOs, wave drift force and added mass matrix were calculated using the frequency
domain diffraction analysis program, AQWA. The gyradius of the vessel was estimated for roll, pitch
and yaw respectively. Any small trim angles have been neglected in the AQWA modelling. The
amount of damping has been calculated by using the Ikeda’s prediction method which computes the
total damping from the frictional, the wave, the eddy and the bilge keel components.
The vessel motions in a seaway have been analysed using a de-coupled frequency domain plus
coupled time domain analysis. The vessel response characteristics, including RAOs and QTF
(Quadratic Transfer Function) matrix, were calculated using the frequency domain diffraction analysis
program, AQWA. The vessel response and design environmental parameters were then input into the
coupled time domain analysis program, Orcaflex. Three-hour simulations have been carried out to
determine the motions see Figure 17.
Figure 17: Orcaflex output showing vessel animation
2.1.1.3
Brazil
The sea states were determined using the sea area boxes defined in the DNV publication (DNV,
2010). The relevant sea area boxes were identified by plotting the voyage route on the sea area map
in DNV C205. The exposure of the vessel to each sea state was determined by the time spent in each
box. Figure 18 shows the sea area boxes traversed by the vessel from Brazil to China (shown by red
track) where each node point represents one day’s travel.
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Figure 18: Voyage route Brazil to China
The significant wave height was determined using a probability of exceedance of 5% with Weibull
coefficients for the relevant sea state taken from DNV C205 and is shown in Table 1.
Table 1: Significant wave height for Brazil to China Voyage
Area
Days
5% Exceedance
20% Exceedance
Hs (m)
Tz (secs)
Tp=1.4*Tz
Hs (m)
Tz (secs)
Tp=1.4*Tz
66
4
3.8
8
11.2
2.8
7.5
10.5
67
3
3.9
8
11.2
2.9
7.5
10.5
84
3
4.8
9
12.6
3.6
8.5
11.9
89
2
6.6
9.5
13.3
4.2
9
12.6
85
1.5
5.8
9.5
13.3
4.2
9
12.6
90
3.5
6.7
9.5
13.3
4.4
9
12.6
75
2
5.2
8.5
11.9
3.5
8
11.2
76
6.5
5.3
9
12.6
3.6
8.5
11.9
70
2.5
4.2
8.5
11.9
2.9
8
11.2
61
2
3.8
7
9.8
2.6
6.5
9.1
62
4
4.1
6
8.4
2.4
5.5
7.7
40
2.5
5.3
7.5
10.5
3.3
6.5
9.1
41
1.5
5.3
7.5
10.5
3.4
7
9.8
28
2
4.8
6.5
9.1
2.7
5.5
7.7
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The analysis was undertaken using the 180 kDWT Capesize Bulk Carrier as shown in Figure 19. The
vessel was in the Full Load condition as defined in the vessel’s Trim and Stability Book and the ship
speed was 15 knots. The analysis routine was run with three different ship headings: Head seas, Bow
seas and Beam seas. Weather avoidance was not taken into consideration. Ship RAOs for the
Capesize vessels were calculated using lines plan, mass distribution, stiffness and damping
coefficients derived from information provided by the shipbuilder: Surge motions (along the
longitudinal axis of the ship) are ignored in this analysis.
Figure 19 : 180 kDWT Capesize bulk carrier
The measurement plane was the transverse plane normal to the ship centreline passing through the
mid-length of Hold No 1. Two measurement points were defined as shown in Figure 20. Point A is the
intersection of the hopper tank side with the side of the material stow. Point B is a point on the bottom
of the hold on the ship centreline.
Point A
Point B
32 m
45 m
15 m
2m
Figure 20: Capesize midship section
A conical material stow in a midships hold with a stow height of 15 m was used. The geometry of the
material stow in Hold No 1 will be more constrained due to the shape of the ship’s hull and will be
governed by both the volume of material in the hold (from the ship’s Trim and Stability Book) and the
natural angle of repose of the material. This means that Point A may rise and may be at the
intersection of the material stow with the ship’s side rather than the hopper tank.
In addition to the full-scale measurements, the accelerations at two points in the cargo stow in Hold No
1 of a Capesize vessel were predicted for a typical voyage from Brazil to China using sea state data
from the DNV Code CP 205 “Environmental Conditions and Environmental Loads”. The accelerations
at each of points A and B will be the summation of each of the relevant vertical and horizontal
components of the roll, pitch, heave and sway motions.
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2.1.2
2.1.2.1
Results
Australia - A
The results in Table 2 and Figure 21 show the mean values of wave height, roll, pitch and vertical and
transverse accelerations at St16 (Hold 1) and indicate that on the South American and African routes
the mean wave height is about 50% higher than on the Australia-China route.
Table 2: Summary of route, conditions and vessel behaviour per m Hs
Number of trips
Mean Distance
Mean Duration
Mean Speed
Sign.Wave Height
Roll
Pitch
V.Acc.St 16
Tr.Acc.St 16
Australia > China
Brazil > China
Guinea > China
205kDWT Handymax 205kDWT Handymax 205kDWT Handymax
235
298
177
299
299
299
[N.Miles]
3831
3833
11556
11512
11534
11532
[hours]
423
450
1309
1383
1346
1450
[knots]
9.1
8.5
8.8
8.3
8.6
8.0
SDA z (hs)
[m]
1.538
1.67
2.34
2.397
2.299
2.333
SDA f
[deg]
0.852
1.85
1.847
3.065
1.626
3.049
SDA q
[deg]
0.223
0.277
0.464
0.995
0.451
0.974
SDA az16 [m/s2]
0.111
0.356
0.221
0.416
0.23
0.464
SDA ay16 [m/s2]
0.108
0.578
0.325
0.547
0.293
0.544
Considering the ship behaviour the motions of the 205 kDWT vessel are approximately half those of a
Handymax ship and because the Australian route is less exposed to swell, the effect of ship size is
much larger on this route.
Figure 21: Summary of mean conditions and vessel behaviour
The SDA values from the individual steps in the simulations were sorted to obtain a more quantitative
impression of the encountered ship behaviour of both ships on the three routes including the mean
values, the most probable extreme for a single trip and the level which is exceeded in 1% of the trips,
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and the results are shown in Figure 22. Considering the “edges” of the scatter plots of the SDA values
it is clear that the differences are much smaller than observed in the foregoing mean values.
Encountered Wave Height
Encountered V.Acceleration
SDA Hs [m]
12
205kDWT-Mean
10
Handy-Mean
8
205kDWT-M.Pr.
6
Handy-M.Pr
4
205kDWT-1%Extr
2
SDA V.Acc.[m/s^2]
14
Handy-1%Extr
0
Aus
Braz
4.5
4
3.5
3
2.5
2
1.5
1
0.5
0
Guin
205kDWT-Mean
Handy-Mean
205kDWT-M.Pr.
Handy-M.Pr
205kDWT-1%Extr
Handy-1%Extr
Aus
Encountered Roll
Guin
Encountered Tr.Acceleration
6
35
205kDWT-Mean
30
25
Handy-Mean
20
205kDWT-M.Pr.
15
Handy-M.Pr
10
205kDWT-1%Extr
5
Handy-1%Extr
0
SDA Tr.Acc.[m/s^2]
40
SDA Roll [deg]
Braz
5
205kDWT-Mean
4
Handy-Mean
3
205kDWT-M.Pr.
Handy-M.Pr
2
205kDWT-1%Extr
1
Handy-1%Extr
0
Aus
Braz
Guin
Aus
Braz
Guin
Figure 22: Mean, most probable voyage and 1% extreme SDA values
The conclusion of this work is that the extreme values are very similar for the three routes. The effect
of ship size is in the order of 30%. Considering the discontinuity in the cumulative distribution of the
wave height on the Australian route, it is concluded that typhoons (which were included in the
simulations) play a role in the results, although weather avoidance measures taken by the vessels
Master to minimise extreme motions has a significant impact in reducing the sea states encountered
through good seamanship.
With the significant volume of seaborne bulk trade there is likelihood that a TRS cannot be avoided or
that a large storm system takes an unforeseen path and intercepts the vessel. The maximum
encountered values in the simulations for the severest track are given in Table 3 below. The results
are relevant for all routes as the situation is driven by an unforeseen event that is not specific to any of
the three routes.
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Table 3: Maximum encountered SDA values for 300 voyages
Ship
Season
Handymax
Dec-Mar
Apr-Nov
205 kDWT
Dec-Mar
Apr-Nov
Hs (m)
Roll (deg)
Az-bow (m/s2)
EI
9.0
EI
37.4
EI
4.6
EI
8.4
EI
31.6
EI
4.5
EI
7.9
EI
30.4
SCS
4.2
SCS
10.6
SI+SA+SCS
25.0
SCS
3.5
SA
12.2
SCS
49.4
SA
5.9
SA
10.9
SCS
43.9
SCS
5.6
SCS
10.5
SA
33.5
SCS
5.0
EI
9.7
EI
26.3
SI
2.7
SI
8.6
SI
23.2
SI
2.3
EI
8.4
SA
21.3
EI
2.3
SI
12.9
SA
28.8
SI
4.1
SI
10.7
SI
27.5
SI
4.0
SA=South Atlantic, SI=South Indian, EI= East Indian, SCS=South China Sea
The results suggest that the vessels encounter some unfavourable weather in the Eastern Indian
Ocean during the Dec-Mar sailing period, and in the South China Sea during the Apr-Nov sailing
period. The maximum encountered wave heights are consistent between the Handymax and the 205
kDWT vessels, as may be expected. The extreme roll motions of the Handymax, encountered on the
South China Sea are rare events as the next highest are in the South Atlantic Ocean.
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2.1.2.2
Australia - B
Results for the calculated vessel motions are summarised in Figure 24 to Figure 26. Figure 24 and
Figure 25 show the effect of changing vessel orientation to the wave direction on vessel roll and pitch.
In terms of vessel roll changing direction relative to the approaching waves may result in reduction of
roll by 10 – 15 degrees. Vessel pitch is also affected, with Handysize vessels showing a halving of
pitch, while Capesize vessels see a somewhat lesser impact.
Figure 23: Wave heading convention
13,000t Handy
19,000t Handy
170,000t Cape
Figure 24: Effect of wave direction on vessel roll
13,000t Handy
19,000t Handy
170,000t Cape
Figure 25: Effect of wave direction on vessel pitch
Translating the vessel motions into accelerations reveals that the longitudinal (surge) accelerations
are insignificant compared to transverse (sway) and vertical (heave) accelerations (Figure 26). In all
sea state cases the calculated accelerations are less than 1G (9.81m.s-2).
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Figure 26: Calculated vessel accelerations at hold 1 (double amplitude)
Figure 27 shows a three hour, 1 Hz time series plot of vertical accelerations at hold 1 of a Capesize
vessel, in a 95% confidence DNV Zone 100 sea state.
Figure 27: Capesize vessel, vertical accelerations at hold 1, in DNV zone 100 sea state
When comparing vertical accelerations between Capesize and Handysize vessels in the same sea
state, Handysize vessels experience greater accelerations. These accelerations for Handysize vessels
increase in vertical acceleration is approximately 20% as seen in Figure 28 below.
Figure 28: Comparison of the maximum vertical accelerations for Capesize and Handysize
vessels in the same sea state (double amplitude)
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2.1.2.3
Brazil
The output of the analysis comprised the vertical and horizontal components of accelerations at points
A and B in the hold (Figure 20) together with the phase angle between the two components. A typical
set of results is shown in Table 4.
Table 4: Single amplitude standard deviation of different response in different area along route
(bow quartering, 5% exceedance of incident waves)
Area
66
67
84
89
85
90
75
R1
0.22
0.226
0.271
0.363
0.317
0.367
0.299
R2
0.281
0.289
0.431
0.628
0.552
0.639
0.433
R3
0.244
0.251
0.298
0.398
0.347
0.402
0.331
R4
0.229
0.235
0.379
0.562
0.495
0.572
0.369
R5
0.656
0.676
0.791
1.05
0.917
1.06
0.883
R6
0.286
0.294
0.478
0.715
0.629
0.728
0.464
Area
76
70
61
62
40
41
28
R1
0.3
0.239
0.205
0.17
0.299
0.299
0.235
R2
0.476
0.349
0.206
0.146
0.34
0.34
0.213
R3
0.33
0.264
0.231
0.193
0.334
0.334
0.265
R4
0.418
0.298
0.138
0.0623
0.257
0.257
0.118
R5
0.876
0.706
0.624
0.515
0.902
0.902
0.714
R6
0.528
0.374
0.172
0.0696
0.322
0.322
0.144
Table 5 provides a description of the responses used in Table 2.4 and their units.
Table 5: Description of responses
Response
Description
Unit
R1
Sway acceleration at point A
m/s2
R2
Heave acceleration at point A
m/s2
R3
Sway acceleration at point B
m/s2
R4
Heave acceleration at point B
m/s2
R5
Roll
deg
R6
Pitch
deg
The phase angles between components are shown in Figure 29.
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Figure 29: Phase angles between heave and sway accelerations for vessel in bow quartering
seas
2.2
Measured Vessel Motions and Forces
2.2.1
Introduction and methods
Each TWG member has instrumented a number of vessels to be able to directly measure the forces
experienced by the cargo on voyages. The following section outlines each member’s approach and
results of onboard accelerations.
2.2.1.1
Australia - A
Two ships were equipped with measurement equipment to capture the onboard accelerations. Both
ships are Capesize Bulk Carriers, the first vessel is 175 kDWT, and the second vessel 205 kDWT.
Both vessels were equipped with a similar set of sensors aimed to capture motions, accelerations and
vibrations along the length of the hull in addition to navigational parameters as position, speed and
heading. The sensor arrangement is shown in Figure 30.
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Figure 30: Sensor arrangement
The fore and aft sensors include rate gyroscopes to capture the torsion and rolling motion of the
vessel. All five locations have X, Y, Z low noise Monitran MTN/7200 series, -2/+2g range in a joined
triaxial assembly, accelerometers to determine vibrations. Accelerometer sensors were installed at
the centerline at the aft hatch coaming of hold numbers 1, 3, 5, 7 and 9. The location on the aft hatch
coaming and the accelerometer housing are shown in Figure 31.
Figure 31: Accelerometer assemblies at each hold
Data digitization was done locally with distributed I/O modules to avoid electric noise. Local units were
linked digitally with Profibus interface to a central logging unit (main cabinet) at the bridge for data
storage on a laptop computer. Figure 32 shows the details of the main and instrument cabinets.
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Figure 32: Vessel motion instrumentation (a) main cabinet, (b) instrument cabinet with gyro &
accelerometer
Data from the sensors was captured throughout each voyage, together with navigational data from the
vessel system. A video camera was installed in the wheelhouse to record wave and general
conditions experienced by the vessel. All voyage data is downloaded when in port, then analysed to
determine vessel accelerations and contributions from rigid body motions, engine and propeller
vibrations and hull dynamics. Wave conditions are hindcasted using the logged track of the vessel. A
commercial meteorological office was consulted for this data.
2.2.1.2
Australia - B
In order to provide data for the monitoring and reporting of the wave response motions of iron-ore
laden bulk carriers, Australia B has installed OMC International "iHeave" units on five bulk carrier
vessels; four Capesize and one Handysize. The iHeave is a convenient, self-contained vessel motion
measurement unit developed for measuring vessel wave response motions. The devices continually
monitor the motion of the ship in six degrees of freedom and allow calculation of the local motions and
accelerations experienced by cargo at arbitrary hold locations. To 31 October 2012, a total of 21
voyages were recorded on board the five instrumented vessels, including iron-ore laden voyages from
Port Hedland (WA) to Port Kembla (NSW) and Whyalla (SA) to China. Approximately 250 days of
vessel motion data has been processed. The voyages where the iHeave units were deployed are
shown in Table 6. The location of the iHeave units on each voyage are given in Table 7.
Table 6: Vessel iHeave deployments
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Table 7: iHeave installed positions and voyage data
One transit of a laden bulk carrier (the “Capesize C”) from Port Hedland (WA) to Port Kembla (NSW)
was subject to more detailed measurements and analysis. Additional measurements included
deployment of multiple high-precision DGPS instruments which were used to verify the correct
operation of the bridge-mounted iHeave instrument as well as evaluating the level of flexure
experienced by the vessel. The location of each device is shown in Figure 33.
Figure 33: Capesize C instrument locations
All GPS receivers were Trimble R7 Dual Frequency GNSS receivers. GNSS stands for Global
Navigation Satellite System, which is a generic term designed to encompass both GPS and
GLONASS satellite navigation systems. Both L1 and L2 carrier frequencies of the GPS network were
logged. The receivers were configured to determine and log positions at a frequency of 10Hz. The
GPS receiver accuracy is shown in Table 8.
Table 8: GPS Positioning Specification
WaMoS II wave radar recorded the waves encountered by the vessel for use in numerical ship motion
calculations. Finally, an array of vibration sensors was also deployed on deck and in a cargo hold to
establish the significance and source of higher frequency vibrations.
Both high and low-pass frequency band filtering on the measured data are employed in the processing
to remove bias (signals with long periods) and noise (periods less than 2 seconds) respectively. For
motions other than yaw, the bias filter is set to remove signals with periods longer than 45 seconds.
The yaw signal bias filter is set to 20 seconds. The Kalman filter settings on all iHeave units are set to
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the factory defaults. All displacements and rotations are expressed in relation to the vessel navigation
frame of reference, such that the origin of the coordinate system moves with the slow (low frequency)
ship motions and the Z axis is always oriented parallel with gravity. Gravity is excluded from vertical
accelerations.
The displacements and accelerations of specified hold points are estimated by the processing
software. Accelerations are calculated using numerical differentiation of the axial displacements. The
vertical accelerations are produced for a virtual "extreme hold point" on the longitudinal forward
bulkhead of Hold 1 (to capture maximum pitch movement), the maximum hold transverse extent from
the centreline (to capture maximum roll movement), and on the tank top of Hold 1. These
accelerations provide an indication of the overall effect of the vessel motions.
To test for evidence of hull flexure, six GNSS receivers were positioned on deck. From the postprocessed GPS positions, time series of first order vertical, horizontal and torsional flexure modes
were extracted and were band-pass filtered between 0.022 Hz (45 s) and 5 Hz (0.2 s) to remove
signal noise and long period signals. A spectral analysis was performed on the filtered time series to
detect any frequency patterns.
As a first order approximation of the vertical hull flexure, the vertical motion of the bow GPS receivers
relative to the bridge and mid GPS receivers was computed from the post-processed GPS positions:
 For each instant in time (every 0.1 s) a reference plane was constructed through the positions
of the port bridge receiver, the starboard bridge receiver and a virtual receiver half way between
the portside and starboard side mid receivers. The position of this virtual receiver was computed
by averaging the positions of the mid portside and starboard receivers at each instant in time.
 A virtual bow receiver was also generated by averaging the positions of the port and starboard
bow receivers for each instant in time.
 The vertical motion of the virtual bow receiver relative to the reference plane was computed at
each instant in time.
The vertical motion of the bow relative to the reference plane represents the first order vertical hull
flexure.
Similar to the vertical hull flexure analysis the motion of the GPS receivers relative to a reference
plane were computed to test for the presence of horizontal hull flexure:
 For each instant in time, a reference plane was constructed halfway between the port and
starboard mid receivers at hold 5. The reference plane is oriented perpendicular to the
(instantaneous) vector from the port to the starboard mid receivers.
 A virtual bridge receiver was generated by averaging the positions of the port and starboard
bridge receivers for each instant in time.
 The distance of the virtual bridge and bow receivers relative to the vertical reference plane
were computed for each instant in time.
From the post-processed GPS positions of the six GPS receivers, torsional hull flexure was estimated
by comparing roll motions at three positions along the vessel’s hull:
 Aft using port and starboard bridge receivers.
 Amidships using the port and starboard mid receivers in the vicinity of Hold 5.
 Forward using the port and starboard bow receivers on the forecastle deck.
The roll motions at the three positions were compared to detect the presence of the first and second
mode of torsional hull flexure modes:
 First mode: Comparison of bridge and bow roll motions.
 Second mode: Comparison of bridge, mid and bow roll motions.
2.2.1.3
Brazil
Full-scale ship motions and accelerations were measured on voyages of Capesize Bulk Carriers
sailing from Brazil to the Far East to provide context to the laser scan data and pore water pressure
measurements. A Motion Response Unit (MRU) and accelerometers were installed on board each
vessel undergoing full-scale monitoring in locations shown in Figure 34. The sampling frequency of the
MRU is 10 Hz and that of the accelerometers 25 Hz. The 3-axis digital accelerometer (13 bit
resolution) has a working range ±15 g at temperatures between -20 to +65 °C and has an accuracy of
±0.15 g (+25 °C).
17-Mar-13
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The MRU was located on the bridge of the vessel and continuously monitored the ship’s motion in 6
degrees of freedom. Accelerometers were bonded to structural members in the Bosun's Store and in
Hold No 5 amidships to measure accelerations along the three principal axes of the ship - longitudinal
(X-direction), transverse (Y-direction) and vertical (Z-direction). In addition, an accelerometer was
located in Hold No 1 at mid-height in the cargo material to measure accelerations within the material
stow.
Figure 34: Location of vessel monitoring instruments
The data from the MRU and accelerometers was analysed at the end of each voyage to determine
typical amplitudes and periods of ship motion and acceleration.
2.2.2
2.2.2.1
Results
Australia - A
For Gaussian signals on board ships, significant double amplitudes are indicative of the maximum
acceleration that can be expected in a period of 15 to 30 minutes. The measured accelerations are
very mild, an example is shown in Figure 35. Transverse accelerations dominate which is probably
caused by the combined effect of earth gravity and rolling motions of the ship. Longitudinal
accelerations are mildest and never exceed 1 m/s2. Vertical accelerations on one occasion rise to 2
m/s2 but are under 1 m/s2 for the majority of time.
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Figure 35: Significant double amplitudes all sensors
An example voyage is shown in Figure 36. This roundtrip started in ballast at port Kawasaki –
Yokohama, passed Dampier, and ended in Fukuyama works – Kobe Japan. The voyage route and
sensor results are also shown in Figure 36. During the ballasted run some roll was endured. The track
(green) reveals that no course deviations alterations were done to minimize or avoid weather. The
loaded transit took the vessel past Okinawa on a slight detour. Motions were moderate during the
loaded transit in particular. Just prior to arrival in Japanese waters, roll response peaked to 4 degrees.
After that the vessel free floated awaiting the berth. Weather conditions in that period were good.
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Figure 36: Voyage #1 track overview
Circles on the graphs above highlight periods of interest during the voyage due to peaks in vessel
motions. For each of the highlighted events, the following data are represented for a period of 30
minutes:
Time series for:
 surge, sway, heave, roll pitch and yaw.
 Accelerations at the sensor locations.(5* x, y, z)
Frequency spectra for:
 Surge, sway, heave, roll, pitch and yaw motions
 Accelerations at the sensor locations
Hull vibrations, engine- and propeller-harmonics stand out clearly from the noise floor at lower
frequencies (0-15 Hz). At higher frequencies there is increasing energy in the measured data. Figure
37 provides an example of the acceleration spectra. All acceleration spectra figures show from left to
right, x (longitudinal), y (transverse) and z (vertical) accelerations. S1 to S5 indicate the sensors
locations from stern to bow.
17-Mar-13
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Figure 37: Example acceleration spectra
The following frequencies are observed:



0.1 Hz area: the accelerations due to rigid body motions. These are orders of magnitude
higher than the vibration contributions, in particular the vertical and transverse direction
accelerations compared to longitudinal motion.
0.5, 1 and 1.5 Hz: Contributions from hull vibrations.
5 - 10 Hz: Propeller blade and engine harmonics.
The energy content at higher frequencies is coming from high frequent noise. Correlation analysis
shows that the content in incoherent and thus related to local effects including local pumps, working of
hatch covers etc. The data recorded to date has not identified any whipping events, however lengthy
periods of monitoring are required to capture one significant whipping event, and as such, monitoring
is planned to continue for several years.
Figure 38 shows the measured motions and Figure 39 shows the measured acceleration spectra for
event 4 in voyage 1. Figure 40 and Figure 41 are motions and accelerations spectra for event 8 during
voyage 2. The motion data shows that the period of rigid body motions is about 0.1 Hz.
All results show that the rigid body motions are orders of magnitude higher than engine vibrations. The
rigid body motions measured in all voyages to date are small, with the maximum roll being 10 degrees
and the average closer to 3 degrees. Motions and acceleration were small in the longitudinal direction
with a maximum pitch of about 1.5 degrees. Vertical accelerations peaked at 2 m/s2 with an average
less than 0.5 m/s2. Similarly the transverse accelerations peaked at about 3 m/s2 with an average less
than 0.5 m/s2.
Weather avoidance by the Master must be considered as the most recent voyage undertaken on an
instrumented vessel occurred when a cyclone was off the West Australian coast and the loaded ship
was departing port. In this case, the Master adjusted course to maintain a minimum distance of 150
miles from the storm. The vessel still encountered heavy seas, with near gale force to gale force winds
initially on the port quarter and then on the port beam causing moderate rolling and shipping seas
quite heavily on deck. However, these seas were significantly less than what would have been
experienced if the original course through the path of the storm was taken.
17-Mar-13
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Event #04 // Vyg 1 - 0.8 deg pitch - loaded - 10 knots
Hdg 20 deg -.- Spd 11.2 knt
Spectra
0.4
0.3
[m2.s]
Surge [m]
2
0
0.2
0.1
-2
0
0
200
400
600
800
1000
1200
1400
1600
1800
0
0.1
0.2
0.3
0.4
0.5
0
0.1
0.2
0.3
0.4
0.5
0
0.1
0.4
0.5
1.5
[m2.s]
Sway [m]
2
0
1
0.5
-2
0
0
200
400
600
800
1000
1200
1400
1600
1800
8
6
[m2.s]
Heave [m]
2
0
4
2
-2
0
0
200
400
600
800
1000
Time [s]
1200
1400
1600
1800
0.2
0.3
Frequency [Hz]
Spectra
20
5
15
[m2.s]
Roll [m]
Event #04 // Vyg 1 - 0.8 deg pitch - loaded - 10 knots
Hdg 20 deg -.- Spd 11.2 knt
10
0
10
5
-5
-10
0
0
200
400
600
800
1000
1200
1400
1600
1800
0.1
0.2
0.3
0.4
0.5
0
0.1
0.2
0.3
0.4
0.5
0
0.1
0.4
0.5
10
[m2.s]
0
5
-1
-2
Yaw [m]
0
1
0
0
200
400
600
800
1000
1200
1400
1600
1800
2
0.8
1
0.6
[m2.s]
Pitch [m]
2
0
-2
0.4
0.2
-1
0
0
200
400
600
800
1000
Time [s]
1200
1400
1600
1800
0.2
0.3
Frequency [Hz]
Figure 38: Motion data event 4, voyage 1 - loaded
Event #04 // Vyg 1 - 0.8 deg pitch - loaded - 10 knots
Hdg 20 deg -.- Spd 11.2 knt
0
10
0
10
-1
-1
10
Spectral density [ 10log (m/s 2)2.s ]
-2
-2
-3
-2
10
-3
-3
10
-4
10
-4
10
-4
10
-5
10
-5
10
-5
10
-6
10
-6
10
-6
10
-7
10
10
10
10
10
-7
0
2
4
6
freq [hz]
8
10
10
S1
S2
S3
S4
S5
-1
10
10
0
10
-7
0
2
4
6
freq [hz]
8
10
10
0
2
4
6
freq [hz]
8
10
Figure 39: Measured acceleration spectra event 4, voyage 1 - loaded
17-Mar-13
Page 46 of 103
Event #08 // Vyg 2 - 6 deg roll - loaded - 10 knots
Hdg 11 deg -.- Spd 10.4 knt
Spectra
0.1
[m2.s]
Surge [m]
2
0
0.05
-2
0
0
200
400
600
800
1000
1200
1400
1600
1800
0
0.1
0.2
0.3
0.4
0.5
0
0.1
0.2
0.3
0.4
0.5
0
0.1
0.4
0.5
20
15
[m2.s]
Sway [m]
2
0
10
5
-2
0
0
200
400
600
800
1000
1200
1400
1600
1800
1
[m2.s]
Heave [m]
2
0
0.5
-2
0
0
200
400
600
800
1000
Time [s]
1200
1400
1600
1800
Spectra
10
200
5
150
[m2.s]
Roll [m]
Event #08 // Vyg 2 - 6 deg roll - loaded - 10 knots
Hdg 11 deg -.- Spd 10.4 knt
0
200
400
600
800
1000
1200
1400
1600
1800
0.6
[m2.s]
0.8
1
0
0.1
0.2
0.3
0.4
0.5
0
0.1
0.2
0.3
0.4
0.5
0
0.1
0.4
0.5
0.4
0
0
200
400
600
800
1000
1200
1400
1600
1800
2
0.4
1
0.3
0
0.2
0.1
-1
-2
0
0.2
-1
[m2.s]
Pitch [m]
0
0
2
-2
Yaw [m]
100
50
-5
-10
0.2
0.3
Frequency [Hz]
0
0
200
400
600
800
1000
Time [s]
1200
1400
1600
1800
0.2
0.3
Frequency [Hz]
Figure 40: Motion data event 8, voyage 2 - loaded
=
Figure 41: Measured accelerations event 8, voyage 2 – loaded
17-Mar-13
Page 47 of 103
2.2.2.2
Australia - B
The majority of the Australia B vessel motion data was captured for the journey Port Hedland to Port
Kembla. However, voyages from Australia to Europe, US, China and Japan in Capesize and
Handysize vessels carrying other bulk solid cargoes have also been captured. The voyages recorded
are shown in Figure 42.
Figure 42: Recorded vessel motion routes
Ship motion monitoring data collected to date indicate that vessel motions are affected by exposure to
swells from the Southern Ocean. Figure 43 shows that the accelerations were most severe at the
outer (port or starboard) extremities of cargo hold number 1 (most forward), with vertical accelerations
more severe than horizontal accelerations. Vertical accelerations in the range of 1.0 to 6.0 m/s2 have
been estimated for the voyages recorded and up to 4.6 m/s2 for the iron ore laden voyages.
Figure 43: Magnitude of vertical accelerations by hold in a Capesize vessel
Conditions encountered during the voyage of the "Capesize C" were fairly typical, with wave heights of
up to 6 m along with lengthy periods of waves below 2 m. Recorded vessel motions were moderate.
Pitch angles peaked at 3.3 degrees, roll at 8.0 degrees, and heave at 5.8 m. Hold accelerations
peaked at 2.6 m/s2. These values are fairly typical of the voyages reported. An example of a voyage’s
measured vertical accelerations is given in Figure 44 and an example of the measured roll is given in
Figure 45.
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Page 48 of 103
Figure 44: Vertical accelerations from measured vessel motions (double amplitude)
Figure 45: Measured vessel roll
Analysis of the high-precision DGPS data confirms the correct operation of the bridge-mounted iHeave
and associated post-processing, with errors in the iHeave-derived ship motions and local
accelerations generally limited to 0.2 m/s2 and 20-40% RMS error for horizontal (surge, sway, and
17-Mar-13
Page 49 of 103
yaw) and 10% RMS error vertical (heave, pitch, and roll) motions. Analysis reveals that the greater
error in the iHeave results for horizontal motions is due to lower accuracy raw data recorded by the
iHeave IMU in these directions.
Analysis of the DGPS data confirms that, under the conditions experienced during the voyage of the
"Capesize C", hull flexure was extremely limited and did not significantly degrade iHeave-based cargo
accelerations and displacements.
Vertical flexure of the bow of up to approximately 0.2 m was observed (Figure 46), with horizontal
flexure limited to less than 0.08 m (Figure 47). Torsional hull flexure was below measurable limits
(Figure 48).
Figure 46: Simplified schematic of vertical hull flexing
Figure 47: Horizontal hull flexure
17-Mar-13
Page 50 of 103
Figure 48: First mode torsional hull flexure
Wave radar measurements (Figure 49), numerical model predictions and visual observations during
voyage of wave height, period and direction closely resemble each other, although the numerical
predictions did not capture short-duration local fluctuations in wave height.
Figure 49: Wave radar wave height and direction
17-Mar-13
Page 51 of 103
Vibration measurement locations and vertical accelerations are shown in Figure 50 and Figure 51
respectively. Vibration frequencies were limited to the range of 1 – 100 Hz. Vibration levels on deck
and in Hold 4 (Figure 52) were found to be low, all vibration accelerations are reported in millimetres
per second squared (mm/s-2) compared to metres per second squared (m/s2). Near Hold 9 vibrations
were clearly caused by the ship's engine. Further forward the source of the vibrations is less clear and
vibration frequencies appear to reflect the local resonant frequencies of the ship's structure. The mass
of iron ore in Hold 4 damps the natural structural resonances and results in low vibration levels.
Vibration measurement increased during periods of high pitch and roll (Figure 52) however it is likely
that this was primarily due to increased levels of low frequency (<1 Hz) noise in the measurements at
these times.
Figure 50: Vibration sensor locations
Figure 51: Average (single amplitude) vibration accelerations in X(longitudinal / surge),
Y(transverse / sway), Z(vertical / heave) axes
17-Mar-13
Page 52 of 103
Figure 52: Vertical accelerations at the base of hold 4 (ore loaded on top of sensor)
2.2.2.3
Brazil
Throughout the voyage, extracts were taken from the ship’s log recording information on the ship
(speed and heading), sea and weather conditions so that these could be correlated with the motion
and acceleration data. A typical record sheet is shown in Table 9.
Table 9: Ship data and sea state record
This corresponds to the position of the vessel during its voyage shown in Figure 53.
17-Mar-13
Page 53 of 103
Figure 53: Position of vessel during voyage
The corresponding ship motions are shown in Figure 54 to Figure 57.
Figure 54: Roll and pitch motions on hourly basis
17-Mar-13
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Figure 55: Sway and heave motions on hourly basis
Figure 56: Roll and pitch motions on second basis
17-Mar-13
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Figure 57: Heave and sway motions on second basis
The corresponding response spectra are in Figure 58 to Figure 60.
Figure 58 shows the roll response spectrum for a Capesize Bulk Carrier on a voyage from Brazil to the
Far East as recorded by the MRU on the vessel’s bridge. It clearly indicates a peak response at a roll
period of approximately 9 seconds and a further, smaller peak, corresponding to a roll response of
approximately 16 seconds.
The roll response spectrum may be interpreted as showing the natural roll period of the vessel to be
approximately 9 seconds. The secondary peak around 16 seconds is likely to be due to the vessel
responding to a longer encounter period in stern quartering seas.
The Capesize vessel has a natural roll period of approximately 10 seconds or 0.1 Hz (vessel response
– mix of RAO and sea states).
Figure 58: Roll response
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Page 56 of 103
Figure 59: Pitch response
Figure 60: Heave response
Corresponding vessel accelerations for cargo hold 5 are given in Figure 61 and Figure 62. Unless
stated otherwise, the axis convention is as stated in the ‘Abbreviations’ section at the beginning of this
report i.e. X is longitudinal, Y is transverse and Z is vertical. The acceleration responses in each of the
vertical, transverse and longitudinal planes measured at a point amidships in the vessel clearly shows
that the magnitude of acceleration in the vertical and horizontal planes is significantly higher than
those in the longitudinal plane.
17-Mar-13
Page 57 of 103
Corresponding vessel accelerations for Hold 1 are given in Figure 63 and Figure 64.
Figure 61: Cargo hold 5 acceleration time series
Figure 62: Cargo hold 5 acceleration spectra
17-Mar-13
Page 58 of 103
Figure 63: Cargo hold 1 acceleration time series
Figure 64: Cargo hold 1 acceleration spectra
Corresponding vessel accelerations for Bosun’s Store are given in Figure 65 and Figure 66.
17-Mar-13
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Figure 65: Bosun’s store acceleration time series
Figure 66: Bosun’s store acceleration spectra
Springing is resonant hull girder vibrations due to wave-loads where resonant vibrations implies that
they sustain over a certain period (”steady-state” phenomenon) and that there are wave-forces that
oscillate with the same frequency as one of the natural frequencies of the hull girder – usually the
lowest frequency.
Figure 67 is the acceleration response spectrum for a Capesize Bulk Carrier sailing from Brazil to the
Far East. It shows acceleration responses measured at a position approximately 4% of the ship’s
length aft of the forward perpendicular in the frequency range corresponding to the expected two-node
springing frequency. The natural springing frequency is around 0.5 Hz which correlates well with the
calculated frequency of 0.495 Hz. There is clearly a significant ship response at this frequency but
without examination of the acceleration time series it cannot be ascertained whether this is a
sustained springing response or transient whipping response.
Whipping is defined as transient hull girder vibrations due to wave loads that increase rapidly, normally
impact loads that arise from bottom slamming or bow flare slamming. The 2-node and 3-node vertical
vibration modes will normally be the most important.
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Since the Capesize Bulk Carriers have a loaded draft of approximately 18 m and the highest (visually)
recorded wave on their voyages was around 6 m significant wave height, it is unlikely that bottom
slamming occurred. However, the vessels have significant bow flare so it’s possible that bow flare
slamming occurred.
Figure 67: Springing vibration spectra
The ship response spectrum for the main hull girder developed from the accelerations measured
during the full-scale monitoring exercise is shown in Figure 68. It defines a peak at around 0.5 Hz and
a much smaller peak at 5.7 Hz.
Figure 68: Main hull girder response spectrum
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Page 61 of 103
If the main hull girder responds to propulsion train excitation this will be visible at the corresponding
frequencies in the acceleration response spectrum. The critical excitation frequencies for the
propulsion train are as follows:



Propeller blade rate 5.7 Hz
Propeller shaft rate 1.4 Hz
Main engine cylinder rate 8.6 Hz
As can be seen from the hull girder response spectrum the only indication of a propulsion train
response is a very small excitation at propeller blade rate. Based on vessel motions captured at fullscale, only the vertical and the transverse motions are material.
Figure 69 shows the variation in acceleration for a Capesize Bulk Carrier along the ship’s length (L)
from midships to No 1 Hold (12% L aft of forward perpendicular (FP)) and Foc’s’le (4% L aft of FP).
The accelerations increase with increasing distance from amidships. In the case of vertical
accelerations this increase is greater than 80%. Thus, Hold 1 experiences the most extreme
accelerations.
Figure 69: Accelerations along ship length. ACCN SD is Acceleration Standard Deviation
2.3
Comparison and Findings
Based on the work of each of the three TWG members presented, comparisons and key findings can
be drawn. Each members work has essentially confirmed the others findings regarding vessel motions
and forces. The following provides a list of the key comparable results;








17-Mar-13
Contribution from vibrations associated with engines are negligible.
Rigid body motions: based on vessel motions captured and calculated, only the vertical and
the transverse motions are significant.
Capesize vessels have a natural roll period of 10 seconds or 0.1 Hz (based on various RAOs
and response spectra).
Accelerations in Handysize vessels are approximately twice those of Capesize vessels
Hold 1 experiences the largest accelerations.
Real-world accelerations measured during voyages are typically lower than those predicted by
voyage calculations.
The observed vessel movements are less than 1G, typically 0.1G.
Weather avoidance practices reduce the maximum accelerations experienced.
Page 62 of 103
A summary of the accelerations experienced by Capesize, Handymax and Handysize vessels for
various voyage routes is given in Table 10. The results provide confirmation of the possible
magnitudes of the vertical and transverse accelerations occurring during voyages. The two separate
approaches result in similar values with all calculated and measured accelerations being comparable,
and less than, those described by the Code of Safe Practice for Cargo Stowage and Securing (2011),
Annex 13.
Table 10: Summary of vertical and transverse accelerations experienced by Capesize,
Handymax, and Handysize vessels
CAPESIZE
W. Aust - China
HANDYMAX
Extreme Zone
HANDYSIZE
W.
Brazil
Extreme
W. Aust
Extreme
Brazil -
Aust -
-
Zone
- China
Zone
China
China
China
Aust B
Aust A
Aust A
Aust A
Aust B
Aust B
Acceleration
Roll
Aust A
Aust B
Aust A
Max of
5
0.5
1.7
0.5
2.2
1.0
0.7
2.2
2.7
10
1.0
2.0
0.9
2.5
1.2
1.2
1.4
3.1
15
1.5
2.3
1.3
3.1
2.0
1.5
3.7
20
2.1
2.5
1.8
3.3
2.5
2.0
3.5
25
2.6
2.3
3.4
3.0
2.4
30
3.2
2.6
3.7
3.5
3.0
5
0.7
0.9
0.8
1.6
1.0
1.0
0.9
1.9
10
1.7
1.0
1.6
1.3
1.5
1.5
0.5
1.9
15
2.3
1.0
2.4
1.7
2.8
2.5
1.9
20
3.5
1.0
3.2
1.2
3.3
3.2
1.4
25
4.3
4.0
1.4
4.5
4.3
30
5.1
4.3
1.2
5.0
5.0
Aust A
Acceleration
m/s2
(Vertical, Z)
Max of
4.1
4.0
Acceleration
m/s2
(Horizontal
Transverse, X)
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6.0
5.0
Page 63 of 103
3
VESSEL STABILITY
3.1
Introduction
All vessels covered in this report must satisfy the IMO Intact Stability Code criteria in order to trade.
This Code defines the criteria they must meet in the intact condition (i.e., without damage) in order to
be considered stable seagoing vessels.
This section of the Marine Report addresses the question of how a vessel’s stability may be
compromised in the event of the failure of an iron ore cargo.
To answer this question it is first necessary to determine the impact of cargo failure and the mode of
failure on the stability characteristics of the vessel. Once this has been determined, it is then possible
to examine the resultant ship stability from two different perspectives. The first considers the degree
of compliance with international rules and regulations that the vessel retains after cargo liquefaction in
one or more holds. The second investigates the ability of the vessel to remain stable after cargo
liquefaction, even though it may not meet the statutory rules and regulations.
The relative stability characteristics of Capesize, Handymax and Handysize vessels are considered
and the reserves of stability inherent in the design of the most widely used ships for the transport of
iron ore – the Capesize Bulk Carrier – are examined.
This section draws together the results of stability investigations undertaken by the three TWG
members and presents some key findings.
3.2
Methodology
The methodology comprises three stages.
First, the impact of cargo failure on the stability of the vessel is determined and, in particular, the
impact of varying the number of holds affected by cargo failure.
Second, the degree of compliance with international rules and regulations after cargo failure is
examined.
Third, the ability of the vessel to remain stable after cargo liquefaction is investigated.
3.2.1
Stability analysis
Two possibilities for cargo failure have been considered. In the first the cargo is assumed to liquefy
and form a free surface. In the second the cargo is assumed to undergo a progressive shift in one
direction with the roll of the vessel and does not return to centre. These are treated respectively as
“free surface” effect and “cargo shift” effect.
3.2.1.1
Free surface
The effect of the free surface may be considered in one of two alternative ways:
Virtual rise in the vessel vertical centre of gravity (VCG)
The rise in vertical centre of gravity (VCG) is calculated by summing the moment of inertia of all slack
tanks and holds with free surface and dividing by the vessel’s displacement. When using the virtually
raised VCG, the influence on the calculated stability curves (GZ) will be high.
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The virtual rise in VCG is dependent on the specific gravity of the liquid in the tank or hold. For this
reason, a range of specific gravities have been considered in the report ranging from 1.00 (fresh
water) to the bulk density of the material in the hold.
Treating the cargo as “Heavy Liquid Cargo” or “Liquefied Cargo”
By assuming the load as an ordinary liquid, the basic assumption is that the surface of the liquid is
always horizontal and that the heeling moment of the load created as the vessel heels by the change
in centre of gravity is taken directly into account and reflected directly in the righting arm curve (GZ).
This method will not account for the possible shift of the load, but assumes that the load follows the
rolling movement of the ship.
For the purpose of this study it has also been assumed that the liquefied load is homogenous and
occurs simultaneously in specified holds. The corresponding loading condition was modelled in NAPA
with the amount of cargo shift applied as a moment on the vessel to estimate the resulting heel. The
amount of cargo shift has been estimated graphically for various roll angles from 0° to 30°. This
assumes that the free surface of the cargo shift is parallel to the waterline. It has also been assumed
that the entire contents of the hold shifts. This approach is considered to be conservative. Figure 70 to
Figure 72 show the cargo shift for roll angle increments for each hold in a Capesize, and two Handy
size vessels. In these figures the cargo shifts as a liquid to the extent of the roll angle and then is fixed
in that position as a solid. Free surface corrections are then applied to those affected by the cargo
shift.
Figure 70: Capesize vessel roll angle and shift of cargo
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Figure 71: 19,000 t Handy size vessel roll angle and shift of cargo
Figure 72: 19,000 t Handy size vessel roll angle and shift of cargo
Analysis of the static stability resulted in static heel angles of 0° to 15° or even greater could occur as
a result of cargo liquefaction and progressive shift in centre of gravity due to the vessel motions. The
free surface correction based on the transverse actual moment of inertia of the cargo is calculated for
each angle of heel.
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Page 66 of 103
3.2.1.2
Cargo shift
In the cargo shift scenario it is assumed that the cargo shifts and remains in a fixed position.
It should be noted that the cargo shift moment is only applied to the holds considered to have free
surface effect.
3.2.2
Rule compliance
The resultant vessel stability characteristics are examined to determine the degree of compliance with
international rules and regulations after cargo failure.
At this moment, there is no specific intact stability criterion in International Regulations or Codes for
evaluating the conditions caused by the shifting of cargo which has the possibility to be liquefied
during a voyage. In this report the IMO Intact Stability Code has been used to evaluate the free
surface effects on stability. The IMO Intact Stability Code requires the following stability criteria to be
met:

the area under the righting lever curve (GZ-curve) should not be less than 0.055 metre-radians up
to 30 degrees angle of heel.

the area under the righting lever curve (GZ-curve) should not be less than 0.09 metre-radians up
to 40 degrees or the angle of flooding if this angle is less than 40 degrees.

the area under the righting lever curve (GZ-curve) should not be less than 0.03 metre-radians
between 30 degrees and 40 degrees or the angle of flooding if this angle is less than 40 degrees.

the righting lever GZ should be at least 0.20 metre at an angle of heel equal to or greater than 30
degrees.

the maximum righting arm should occur at an angle of heel preferably exceeding 30 degrees but
not less than 25 degrees.

the initial metacentric height G0M should not be less than 0.15 metre.

weather criterion area “b” shall be equal to or greater than area “a” as defined in Figure 73.
.
Figure 73: Severe wind and rolling
17-Mar-13
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The angles in Figure 73 are defined as follows;
φ0 = angle of heel under action of steady wind
φ1 = angle of roll to windward due to wave action
φ2 = angle of down-flooding (f) or 50° or c, whichever is less,
where;
φf = angle of heel at which openings in the hull, superstructures or deckhouses cannot be closed
weather tight are immersed.
In applying this criterion, small openings through which progressive flooding cannot take place need
not be considered as open φc = angle of second intercept between wind heeling lever lw2 and GZ
curves.
The wind heeling levers lw1 and lw2 referred to above are constant values at all angles of inclination
and shall be calculated as follows:
Where;
P = wind pressure of 504 Pa. The value of P used for ships in restricted service may be reduced
subject to the approval of the Administration
A = projected lateral area of the portion of the ship and deck cargo above the waterline (m 2)
Z = vertical distance from the centre of A to the centre of the underwater lateral area or approximately
to a point at one half the mean draught (m)
Δ = displacement (t)
g = gravitational acceleration of 9.81 m/s2
3.2.3
Ship survivability
For the purposes of determining ship survivability the study uses the criterion of the vessel retaining a
positive metacentric height (GM). Where other stability criteria are significantly compromised despite a
positive GM, for example minimal area between the righting lever curve and listing lever curve, then
this is pointed out in the text.
17-Mar-13
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3.3
Results
3.3.1
Typical Capesize Vessel
A typical Capesize vessel as shown in Figure 74, with typical details shown in Table 11, was used in
this analysis. The loading conditions presented in the vessels’ Trim and Stability Books which are
representative of homogeneous iron ore loading have been used for the analysis as shown in Figure
75. The vessels were generally loaded to the scantling draft in this loading condition. The cargo holds
are partially filled by iron ore and the cargo is trimmed.
Figure 74: Typical Capesize vessel used in the stability analysis
Table 11: Typical Capesize vessel details
17-Mar-13
Cargo weight
198,280 tonnes
Fuel weight
2,954 tonnes (50% capacity)
Fresh water
310 tonnes
Constant
471 tonnes
Displacement
231,426 tonnes
Draft
18.176 m (even keel)
GM
13.087 m corrected for free surface
Page 69 of 103
Figure 75: Typical homogeneous load condition in a Capesize vessel
3.3.1.1
Stability analysis
Free surface - Virtual rise in vessel VCG
Table 12 shows the impact of cargo failure on the vessel’s metacentric height by applying a free
surface correction with different specific gravities. Figure 76 shows the righting lever curve when all
holds have a free water surface.
Table 12: Typical Capesize vessel free surface correction
17-Mar-13
No of holds affected
by free surface
Surface liquid
specific gravity (t/m3)
Resultant GM (m)
All
1.00
2.8
All
1.03
2.5
4
2.40
1.7
5 or more
2.40
Negative
Page 70 of 103
Figure 76: Righting lever with full free surface in all holds
Cargo shift
Analysis shows that a cargo shift of 10o in all holds would cause a vertical rise of the cargo’s centre of
gravity of approximately 0.4 m and a horizontal shift of its centre of gravity of about 6.6 m.
The Righting Lever and Listing Lever Curves in Figure 77 indicate the effect of this 10o cargo shift on
the vessel.
Figure 77: Righting lever and listing curve for typical Capesize 10o cargo shift condition
17-Mar-13
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In this scenario the vessel would list 25 but still retain sufficient positive righting lever to remain
stable. Provided there was no further shift of cargo, the righting and listing lever curves indicate that
the vessel could safely roll a further 25 (the maximum for the Angle of Repose of the cargo) and still
retain a positive righting lever.
Cargo shift combined with free surface
When cargo shift is combined with free surface effects analysis shows that if there is liquefaction and
cargo shift in any more than 4 holds there is a danger of the vessel capsizing. The free surface
correction based on the transverse actual moment of inertia of the cargo is calculated for each angle
of heel using the virtual rise in VCG methodology.
3.3.1.2
Rule compliance
Intact condition
Figure 78 shows the reserve of stability in a Capesize vessel when the actual intact stability
characteristics are compared to the IMO Intact Stability Code requirements. It plots for each of the
criteria required under the Code the respective requirements of the Code against the actual values
determined in the stability analysis.
Figure 78: Reserve stability in Capesize vessel
Figure 78 shows clearly that Capesize Bulk Carriers typically have a metacentric height (GM) many
times the value required by the IMO Rules and the areas under the righting lever curve are typically 10
times the rule requirements.
The criterion where the actual value comes closest to the rule requirement is in the maximum GZ
angle but even here the actual angle is more than 60% higher than the rule requirement.
17-Mar-13
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Condition after cargo failure
Table 13 and Figure 79 below summarises the impact of cargo liquefaction in an increasing number of
holds with free surface. With “0” holds subject to liquefaction the vessel is sailing normally, whereas
with nine holds subject to liquefaction there is a free surface in all nine cargo holds.
It shows the outcome of testing the stability characteristics of the vessel against the IMO Intact
Stability Code for increasing numbers of hold affected by cargo failure.
Table 13: Effect on vessel compliance with increasing number of holds affected
No of holds subject
to liquefaction
IMO Intact Stability
Code criteria
Initial heel
(degrees)
0
1
2
3
4
5
6
7
8
9
OK
OK
OK
OK
OK
Fail
Fail
Fail
Fail
Fail
0
0
0
0
0
16
44
Capsize
Capsize
Capsize
“Fail” means that not all intact criteria are met; however the non-compliance (maximum GZ at 25
degrees or more) may not be critical to the survival of the ship.
Figure 79: Effect of cargo failure in increasing numbers of holds and shows the angle of loll
17-Mar-13
Page 73 of 103
Cargo shift
Table 14 shows GM determination for a capesize vessel. GM is calculated on the basis that for
affected holds the ore shifts as a solid with a surface parallel to the waterline and then a free surface
correction is applied to the affected holds using the cargo density. The outcome is that when more
than 4 holds or 50% of cargo are affected in this way the vessel becomes unstable: GM is negative.
This is reinforced by the righting lever curves for the same vessel, shown at Figure 80
Table 14: Capesize vessel GM due to cargo shift by number of holds
Capesize
GM (m)
Intact
10.389
1 Hold
8.714
2 Holds
6.472
3 Holds
4.222
4 Hold
1.971
5 Holds
-0.279
6 Holds
-2.530
7 Holds
-4.780
8 Holds
-7.006
9 Holds
-8.822
Figure 80: Righting lever curves for Capesize vessel
3.3.1.3
Ship survivability
Table 15 collates the results from the various stability analyses and shows whether or not the vessel
survives cargo liquefaction in increasing numbers of holds with failed cargoes. It clearly shows that the
Capesize vessel survives fresh water free surface in all holds and even when that free surface
comprises a dense liquid with SG = 2.4 t/m 3, it requires a free surface in more than half the holds to
cause the vessel to fail. The Capesize vessel can withstand a 10o cargo shift in all holds, and it’s only
when this is combined with a fresh water free surface in more than half the holds, that the vessel
stability is compromised (GM becomes negative).
17-Mar-13
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Table 15: Effect on vessel survivability with increasing number of holds affected
No of holds
subject to
liquefaction
Free surface with
SG = 1.0 t/m3
Free surface with
SG = 2.4 t/m3
Cargo shift of 10
degrees
Cargo shift with
free surface
SG = 1.0 t/m3
1
2
3
4
5
6
7
8
9
OK
OK
OK
OK
OK
OK
OK
OK
OK
OK
OK
OK
OK
Fail
Fail
Fail
Fail
Fail
OK
OK
OK
OK
OK
OK
OK
OK
OK
OK
OK
OK
OK
Fail
Fail
Fail
Fail
Fail
3.3.2
Typical Handymax Vessel
The stability calculations are conducted using information from a 52 kDWT Handymax vessel of
Length 182 m and Beam 32.26 m. The vessel is loaded in a typical condition with an evenly spread
ore cargo. The vessel’s condition is outlined below in Table 16.
Table 16: Typical Handymax vessel details
Cargo weight
Fuel weight
1,130 tonnes (50% capacity)
Fresh water
204 tonnes
Constant
471 tonnes
Displacement
3.3.2.1
50,660 tonnes
60,770 tonnes
Draft
12.02m
GM
7.79m corrected for free surface
Stability analysis
Free surface - Virtual rise in vessel VCG
Table 17 shows the impact of cargo failure on the vessel’s metacentric height by applying a free
surface correction with different specific gravities.
17-Mar-13
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Table 17: Typical Handymax vessel free surface correction
No of holds affected
by free surface
Surface liquid
specific gravity (t/m3)
Resultant GM (m)
All
1.00
1.5
All
1.03
1.4
2
2.40
1.4
3 or more
2.40
Negative
Cargo shift
Analysis shows that a cargo shift of 10o in all holds would cause a vertical rise of the cargo’s centre of
gravity of approximately 0.5 m and a horizontal shift of its centre of gravity of about 4.4 m.
The Righting Lever and Listing Lever Curves in Figure 81 indicate the effect of this cargo shift on the
vessel.
Figure 81: Righting lever and listing curve for typical Handymax cargo shift condition
In this scenario the vessel would list 26 but still retain sufficient positive righting lever to survive.
As a Handymax vessel is capable of rolling to 40 in extreme conditions, the cargo could shift a further
5 to a maximum of 15 from the horizontal. In this case the following conditions apply, with the
resulting righting lever curve shown in Figure 82.
 Vertical shift of centre of gravity of cargo 0.6 m
 Horizontal shift of centre of gravity of cargo 5.5 m
 GM now reduced to 7.29 m due to an increase of the vessel’s VCG
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Page 76 of 103
Figure 82: Righting lever curve for Handymax suffering further cargo shift
These curves now indicate that the vessel would list to 33, if there was a shift of cargo by 15 from
the horizontal, putting it in a dangerous position. The level waterline would submerge the hatch
coamings to half their height, and the vessel would be less than 7 from flooding. The vessel’s down
flooding angle at this draft is 40.
Cargo shift combined with free surface
It can be seen that the Handymax can survive either a situation where water accumulates on the
surface of the cargo or where there is a fairly moderate shift of cargo.
However, when both these conditions are combined i.e. where the cargo has shifted, even by a slight
amount, and there is free surface effect above the stow in all holds, then the vessel will capsize. If the
Handymax vessel with free surface water in all holds plus a shift of cargo to 10 in just one hold
occurs, the following conditions are found and the resulting righting lever curve is shown in Figure 83.
 Weight of cargo shift 10,755 t (No 4 Hold)
 Movement of cargo: Vertically 0.6 m Horizontally 4.35 m
 GM reduced to 1.42 m due to free surface effect and vertical rise of 10,755 t
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Figure 83: Righting lever curve for a combination of free surface and cargo shift
The listing lever intersects with the vessel’s righting lever between 25 and 35 but the remaining
positive lever is virtually zero. The righting lever at 30 is 0.70m and the listing lever at 30 is 0.67 m.
The vessel would not survive a shift of cargo in this condition.
3.3.2.2
Ship survivability
Table 18 collates the results from the various stability analyses and shows whether or not the vessel
survives cargo liquefaction in increasing numbers of holds with failed cargoes. It shows that the
Handymax can survive both fresh water free surface in all holds and cargo shift of 10 degrees in all
holds. The vessel can also survive free surface of a dense liquid with SG = 2.4 t/m 3 in two of five
holds.
However, when both these conditions are combined i.e. where the cargo has shifted, even by a slight
amount, and there is free surface effect above the stow in all holds, the vessel will be compromised.
Table 18: Typical Handymax survival conditions
No of holds subject
to liquefaction
Free Surface
with SG = 1.0
t/m3
Free Surface
with SG = 2.4
t/m3
Cargo shift of 10
degrees
Free surface in all
holds and cargo
shift in specified
hold
1
2
3
4
5
OK
OK
OK
OK
OK
OK
OK
Fail
Fail
Fail
OK
OK
OK
OK
OK
Fail
Fail
Fail
Fail
Fail
3.3.3
Typical Handysize Vessel
Table 19 and Table 20 show GM determination for a handysize vessels. GM is calculated on the basis
that for affected holds the ore shifts as a solid with a surface parallel to the waterline and then a free
17-Mar-13
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surface correction is applied to the affected holds using the cargo density. The outcome is that when
more than 50% of cargo are affected in this way the vessel becomes unstable: GM is negative.
Table 19: 19 kDWT Handysize vessel GM due to cargo shift by number of holds
Handy 19k
GM (m)
Intact (No Liquefaction)
2.308
Cargo Hold 1
2.003
Cargo Hold 2
-0.562
Cargo Hold 1 & 2
-0.868
Table 20: 13 kDWT Handysize vessel GM due to cargo shift by number of holds
3.4
Handy 13k
GM (m)
Intact (No Liquefaction)
2.981
One Forward Cargo Holds
2.469
Two forward Cargo Holds
1.714
Three Forward Cargo Holds
0.400
Cargo Hold 3
1.623
Cargo Hold 3+ One Hold Fwd
0.868
Cargo Hold 3+ Two Hold Fwd.
-0.399
Comparisons and Findings
This report has drawn on investigations undertaken by the members of the TWG into the stability of
Capesize, Handymax and Handysize vessels. There is significant commonality in the outputs of these
investigations which gives strong credibility to the report findings. The key findings of the report are as
follows:



17-Mar-13
For Capesize vessels, stability is not compromised unless more than 50% of the cargo mass
has moved
o The investigations into the stability of Capesize vessels after cargo failure indicate that
Capesize vessels survive fresh water free surface in all holds or a 10 degree cargo
shift in all holds.
o Indeed, such is the reserve of stability in typical Capesize vessels that they retain
positive stability to the point where more than 50% of the cargo material has moved.
Handymax and Handysize vessels are less stable than Capesize vessels when carrying heavy
density cargoes
o The investigations into the stability of Handymax and Handysize vessels demonstrate
that in the condition where cargo shift occurs in all holds and one or more holds are
then subject to free surface effects, the vessel will fail. This compares with the
Capesize vessel which can withstand cargo shift and free surface in up to four of nine
holds before the vessel is potentially compromised.
o This indicates that Handymax and Handysize vessels have a lower reserve of stability
than a Capesize vessel when carrying heavy density cargoes.
Seaborne iron ore trade predominantly employs vessels that have significant “reserve stability”
o More than 90% of iron ore is carried in Capesize vessel. Investigations into the
compliance of Capesize vessel with the IMO Intact Stability Code indicate that such
Page 79 of 103
vessels have a considerable reserve of stability. The study shows clearly that
Capesize vessels typically have a metacentric height (GM) many times the value
required by the IMO Rules and the areas under the righting lever curve are typically
10 times the rule requirements.
17-Mar-13
Page 80 of 103
4
CARGO OBSERVATIONS
The section of the Marine Report describes the cargo observations undertaken by the TWG
companies. In a generic sense, all three iron ore producers have two main types of cargo
observations: normal routine observations and special observations. Special observations are those
taken for a specific purpose (e.g., understanding the impact of TML on IOF).
This section presents the observations undertaken by each company highlighting specific
observations and measurements in relation to cargo behaviour at loading, during transit and at
discharge. Common themes and particular findings are presented followed by specific conclusions.
4.1
Australia - A observations
4.1.1
Introduction and Methods
Over 100 observations of the behaviour of three different IOF product cargoes during ocean transport
have been conducted. The voyage routes are typically from Western Australia to China, however
some have been on vessels travelling from Western Australia to Europe. The vessel voyage
conditions were taken from the Master’s log as well as the Vessels Performance Report (VPR). The
cargo’s appearance was visually recorded after loading was completed and before discharging
commenced. Figure 84 shows examples of the cargo after loading and before discharge. As well as
the visual observations, cargo heights were recorded after loading and before discharge, either by
measuring the height of the cargo at the hold wall and/or by measuring the distance between the
cargo and the hatch covers (ullage). From these measurements an estimation of the percentage
compaction was made. In Figure 84, comparison of the after-loading and before-discharge pink
markings on the walls near the corners showed little to no compaction occurred. Also, the photos
show that there is no evidence of moisture or free water in the corners. Photography of the hold when
the cargo had been almost completely discharged was undertaken to monitor for evidence of cargo
drainage or presence of standing (free) water during the voyage. Figure 85 shows an example of the
cargo hold upon completion of discharging, with no evidence of moisture or standing water on the tank
top.
(a)
(b)
Figure 84: Cargo observed (a) after loading and (b) before discharge
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Figure 85: Photos showing cargo hold conditions at end of discharge
Throughout the voyage the bilges were sounded and the amount of water removed was recorded. An
example of the bilge water removal over a voyage is shown in
Table 21. The total amount of water removed through bilge pumping in this example was 2 tonnes
(2 m³) which is 0.01% of the cargo’s moisture content. This 0.01% can be attributed to condensation
from humid air enroute.
17-Mar-13
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Table 21: Bilge pumping summary
HOLD
HOLD NO.1
m3 or metric tonnes
AMOUNT
Port
Starboard
0.10
0.20
HOLD NO. 2
0.40
0.10
HOLD NO.3
0.10
0.10
HOLD NO.4
0.30
0.30
HOLD NO.5
0.10
0.30
HOLD NO.6
0.00
0.00
HOLD NO.7
0.00
0.00
HOLD NO.8
0.00
0.00
HOLD NO.9
0.00
0.00
TOTAL
2.00 MT
Comments:
Bilges were sounded daily
No bilge water for found for first six days of voyage
Bilge water present each day for last 3 days
No pumping-out water of bilge performed
NOTE:
No.6, 7, 8,and 9 bilges are zero, and no water was found inside bilges
A Leica HDS6200 laser scanner has been employed to accurately map the cargo surface and provide
a profile of the cargo after loading and before discharging. The laser scanning data confirmed the
visual observations of ore compaction and allowed estimation of bulk density and how it changed over
the course of a voyage. An inverted tripod was used to lower the laser scanner down the hold
manhole as shown in Figure 86. Scans were made of the empty hold before loading, the hold after
loading the cargo and the hold after the voyage but before discharging. An example of the laser
scanner output (Figure 87) shows the cargo surface after loading. The surface profiles of the hold
before, during and after loading are then used to determine the cargo volume and, as the mass of ore
in the hold is known from load cells on the ship loading conveyor, the bulk density of the cargo before
shipping is computed. Similarly, the empty hold profile and the profile of the cargo before discharge
are used to determine the bulk density of the cargo after shipping. Also the difference in the
after-loading and before-discharge profile provides the degree of compaction.
Figure 86: location of laser scanner and inverted tripod (inset)
17-Mar-13
Page 83 of 103
Figure 87: Laser scanner profile of cargo surface
Moisture profiling has been carried out by taking successive samples on loading the cargo to
determine moisture as the loading progressed, i.e. at various levels in the cargo in the holds of a
vessel. Similarly, increased sampling was undertaken on discharge of the cargo to determine moisture
as the discharging progressed, i.e. at various levels in the cargo. From these measurements the
moisture profile within the hold was estimated and comparison of on-loading and on-discharging
results allowed identification of any moisture migration that may have occurred during the voyage.
4.1.2
Results
The voyages where observations were undertaken encountered a range of sea conditions. While most
voyages encountered in relatively calm conditions (swell/seas up to 2.0/2.0 metres), some voyages
encountered cyclone or typhoon conditions (swell/seas up to 8.0/8.0 metres). Most extreme weather
occurred in the East China Sea area although some rough conditions were also experienced off the
Western Australia coast.
From the cargo height measurements, the amount of compaction was determined where the cargo
intersected the hold wall, as well as at the cargo peak. The summary of the compaction results from all
100 measurements of the three IOF products are given in Table 22. The results show that compaction
on average is small, around 1% to 4%, with the maximum compaction being about 10%. Other height
differentials may be attributed to very limited dry shift event, though these are negligible. Typically, the
IOF in Hold 1 experienced more compaction than the ore in Hold 9, however this was not always the
case. No correlation between compaction degree and sea condition experienced during the voyage
was found. Most of the compaction of the cargo is due to the loading process (dropping from greater
than 20m). Measurements on partly loaded cargoes show similar bulk densities to fully loaded so the
weight of the material above has a minimal effect.
Survey data in Table 22 is single hold basis and aggregated to average basis. Comparison is valid for
both specific hold (i.e scan vs height measurements) and average of all scans vs average of all height
measurements.
17-Mar-13
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Table 22: Cargo compaction from cargo height measurements
Compaction %
Average
Maximum
Minimum
Hold Wall - Cargo Intersection
Hold 1
Hold 9
1.9
0.7
10.2
3.2
0.0
0.0
Cargo Peak
Hold 1
3.8
10.3
0.5
Hold 9
2.6
7.3
0.1
Observations revealed that no free moisture or saturated iron ore fines (or wet base) were ever
encountered. Sometimes small slips occurred and these were consistently associated with extreme
sea conditions (cyclone/typhoons).
Bilge water volumes and percent of the cargo moisture removed for all observations are summarised
in Table 23. Typically, no bilge water was observed. However, on less than 20% of voyages, small
amounts, of up to 3% of the cargo moisture, were pumped from the bilges. This is equivalent to 0.25%
reduction in cargo moisture, for cargo moisture of 8%. This amount of moisture can be attributed to
condensation, which finds its way to the bilges from bulkheads and metal surfaces in the hold on
sailing from hotter to colder conditions. When bilge water was present, no issues were encountered
pumping out this water, with no blockages of the bilges due to cargo ingress.
Table 23: Bilge water volumes and percent cargo moisture reduction
Bilge Water
Average
Maximum
Minimum
Total Volume from Voyage (m³)
3.3
135.0
0.0
% of cargo moisture reduction
0.01
0.23
0.0
Examples of the laser scanning results are shown in Figure 88 and Figure 89. Figure 88 shows the
results of the scan of the empty hold and Figure 89 shows the result of a scan from hold containing
cargo either after-loading or before-discharging.
Figure 88: Laser scan of empty hold
17-Mar-13
Page 85 of 103
Figure 89: Laser scan of hold containing cargo
An example of the cross section of a cargo obtained from laser scanning of the hold after-loading
(Dampier) and before-discharging (China) is shown in Figure 90. The results clearly show a small
amount of compaction has occurred during the voyage.
Figure 90: Cross section of cargo after loading and before discharge
The laser scanning results for both the cargo compaction and cargo bulk density determinations are
listed in
Table 24. The results are for three IOF products that are shipped from Australia and show that the
compaction determined from laser scanning compared closely with the compaction determined by
cargo height measurements. The bulk density of the cargo increased due to the compaction that
occurs during the voyage, although the average increase was small. Also, from laser scanning the
angle of repose for all three IOF products was similar, at 35° to 37°.
17-Mar-13
Page 86 of 103
Table 24: Laser scanning summary of all hold results for cargo compaction and bulk density
Iron Ore Fines D1
Iron Ore Fines D2
Iron Ore Fines D3
Laser
Scanning
%
Compaction
Initial
Bulk
Density
(t/m³)
Final
Bulk
Density
(t/m³)
%
Compaction
Initial
Bulk
Density
(t/m³)
Final
Bulk
Density
(t/m³)
%
Compaction
Initial
Bulk
Density
(t/m³)
Final
Bulk
Density
(t/m³)
Average
3.1
2.25
2.30
2.3
2.00
2.05
1.9
1.95
2.0
Maximum
8.3
2.28
2.36
9.6
2.10
2.16
10.7
2.06
2.10
Minimum
0.0
2.16
2.20
0.0
1.96
2.01
0.0
1.90
1.93
Cargo moisture profiling results were collated to determine the moisture profile as a function of depth
in the hold on-loading and on-discharging after transport. The changes in moisture were ±0.5% over
the cargo depth of up to 18 m. The measured differences are within the accuracy of replicating the
sampling points and the moisture determination method, hence the conclusion that no moisture
migration took place. All moisture profiling undertaken showed no moisture migration during
transportation of any of the three Australian iron ore fines products. These results confirm the cargo
observation photographs which showed no moisture in the corners of the holds and little to no bilge
water.
4.2
Australia - B observations
Australia B loads iron ore products, lump and fines, only into Capesize vessels. The cargo hold of a
typical Capesize vessel is approximately 45 m wide, 25 m long and 21 m deep, Figure 91 shows an
empty cargo hold from the perspective of a person standing inside on the hold floor.
Figure 91: Capesize C: instrumenting an empty hold
17-Mar-13
Page 87 of 103
Of particular note from Figure 91 are the wear markings on the side of the hold showing the typical
loading pattern of iron ores.
4.2.1
Qualitative Cargo Movement Measurements
To understand whether Australia B iron ore fines moved during transit an initial qualitative approach
was taken. This involved marking the loaded ore boundary against the hold with paint and taking a
photograph. Then upon vessel arrival at the discharge port take another photograph to compare. The
hold markings where made a various points along the port and starboard sides of the vessel. This
process was conducted for a number of voyages. If there was a difference at the discharge port an
attempt to measure the movement was made. The most movement observed during a voyage was
200 mm, however typically the change was negligible as shown in Figure 92. These observations
were conducted for IOF cargoes during April to June 2012.
Figure 92: Capesize vessel hold marking start (left) and end (right) of voyage
4.2.2
Quantitative Cargo Movement Measurements
In order to quantify cargo movement within a hold, an accredited surveying company was engaged to
conduct precise laser scanning of cargo holds prior to loading, upon loading and at discharge port
prior to unloading.
The Terrestrial Laser Scanning of each hold involved two instrument setups in positions that
minimised the data shadows created by the various peaks and troughs of the IOF surface. The two
setup locations where on alternate sides of the hold, the bow and the stern, with one setup placed
towards the port side, the other to the starboard. A high-resolution 360° scan was performed at each
setup, producing three-dimensional point spacing of 6 mm by 6 mm at 10 m. There were two different
scanners used for the project. All scans undertaken at load port were done using a Zoller and Fröhlich
Imager 5010, whereas a Leica HDS6000 was used at the discharge port. Conformance tests to
ensure that the datasets from the two different scanners were comparable were conducted. Cloud to
cloud disparities were <2 mm @10 m, well within instrument specifications. Figure 93 shows the
typical survey setup.
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Figure 93: Capesize vessel cargo laser scanning survey
Altogether more than 21 holds were scanned, of which seven were commissioning related and only
conducted at the discharge port.
Figure 94 shows the raw laser scan from one side of the cargo hold. Note that the laser scan of the
empty hold was able to identify the wear / load marking referred to in Figure 91.
Figure 94: Raw laser scan images from only one instrument setup point
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The contour plots of the cargo surface are shown in Figure 95. Analysis of these contour plots proved
difficult to identify and quantify the subtle cargo movements. To aid interpretation of the start and end
journey survey data, a contour map showing the elevation difference of the surface profile was
constructed (Figure 96). The cargo surface difference map readily highlights the changes between the
loading and discharge scans. In this example the surface difference map shows little if any movement
of the cargo at the edges of the hold, with some minor slumping on the port – aft quarter. Which when
compared back to the original contour plots can be easier to observe.
Figure 95: Capesize vessel cargo survey Hold 1 contours at loading (left) and discharge (right)
Figure 96: Cargo surface difference contour map for hold 1 of a Capesize vessel
One of the vessel surveys was conducted on a vessel fitted with motion accelerometers. Figure 97
shows the key significant (as previously used, this means the average of the highest third of the data,
with the maximum observation equal to approx 1.8 times the significant value) vessel motions for the
journey and the derived vertical accelerations. For a period of the journey there was a problem with
the data collector resulting in data loss.
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For the motions captured during the journey the largest vessel motions were observed near the south
west corner of Australia. Maximum roll observed was about 10 degrees and maximum acceleration
approximately 4 m/s2.
Figure 98 shows the surface difference map for the vessel as a result of this journey. Two holds were
not surveyed at the discharge port.
Figure 97: Capesize journey and key motions heave, pitch, roll translated to vertical
acceleration
Figure 98: Capesize vessel surface change profile due to journey shown in Figure 97
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It becomes apparent from the surface difference profile of the whole vessel that most change in the
cargo surface occurs centrally, being a decrease in surface height, i.e. compaction.
Localised increases in the cargo surface occur in the corners of a hold, though predominantly only in
one corner and not the same corner for all holds. This may suggest the observed surface increase is
more a function of loading profile than vessel movement.
Examination of the surface difference maps and the corresponding scale suggests that for some areas
of the hold there is some minor cargo movement. This movement is predominantly localised to the
centre of the cargo and is a decrease in height, with no consistent increase in cargo height elsewhere.
That is the decrease in height translates to compaction of the cargo and not a shift in cargo position
and therefore not a shift in cargo weight distribution within the hold or vessel.
Analysis of the cargo surveyed volumes and loaded tonnages allow further understanding. In all
measurements the volume decreased from the start to end of voyage. This is includes limited dry shift
events and compaction. The volume change for all surveyed holds is graphed in Figure 99. The
measured volume change is consistent within each product surveyed. Regardless of product, the
volume reduction during the journey is much less than 5%. This volume reduction translates into an
increase in saturation. i.e. for loaded saturation of 40% then the volume decrease will result in cargo
saturation increasing to about 45%.
When the new volume is translated to a product density change (Figure 100), for Australia-B Product
A the density increase is approximately 0.08 t/m3 or as per volume change and only 3%. For AustraliaB Product C the density increase is less than 0.05 t/m3 or 1%.
Figure 99: Volume difference due to 14 day voyage
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Figure 100: Bulk Density Change due to 14 day voyage
4.2.3
Bilge Checks
Regular inspections of vessel bilge wells are conducted throughout a voyage. The bilges are pumped
according to results of the bilge soundings. Negligible water, <0.1% by cargo weight, is pumped from
bilges for Australia B cargo holds. Figure 101 shows some typical bilge pumping data.
Figure 101: Bilge pumping records show little if any free moisture
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4.2.4
Vessel Journey Reports
Vessel journey logs are kept and observations noted. During one the instrumented vessel journeys,
China to Port Hedland a vessel encountered a typhoon and took prudent avoidance action. This was
captured on the vessel motion accelerometers and the track plot shown in Figure 102. The result is
the largest vessel roll encountered was about 10 degrees and vertical accelerations in hold 1 of less
than 4 m/s2.
Figure 102: Vessel behaviour in extreme weather
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4.2.5
Discharge Superintending
Australia B supervises and reports on the discharging operations of its cargoes on a regular basis. An
Inspection Report extract is shown in Figure 103. Whilst only a qualitative indicator for the last twelve
months the inspectors have been noting whether or not evidence of moisture / water was observable
at the bottom of any holds, as highlighted at the bottom of the extract. These inspections covered over
60 fines cargoes loaded into more than 270 holds, from over 30 vessel voyages to 14 different
discharge ports. To date only one hold has been reported as having moisture observed (described as
a puddle) in the bottom corner of the hold. Figure 104 shows the typical unloaded dry floor state.
Figure 103: Example discharge inspection report extract
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Figure 104: Cargo discharge, note dry floor
4.3
Brazil Observations
4.3.1
Laser Scanning
Brazil has undertaken cargo laser scanning on four voyages between Brazil and Singapore / Brazil
and China using a with Leica HDS6000 Scanning Laser instrument. Laser scanning units were
installed within each of the monitored holds to record detailed data on the intensity of changes in the
cargo stow geometry during sea transportation. An example of the cargo laser scan is shown in Figure
105.
The laser scan data has been transposed into three-dimensional profiles to illustrate the surface
features that develop, the global settlement of the stow, the drainage of water from the stow and the
slope instabilities that occur immediately following loading and during transportation. Where
practicable, the cargo was scanned every 15 minutes throughout each separate voyage.
The laser scan data was compared against the significant wave height and pore water pressure data
to identify causal links to surface features, global settlement and slope instabilities.
Further analysis of the laser scanning data was undertaken to provide volumetric assessments, thus
allowing approximate material bulk densities within the hold to be calculated for validation purposes.
The main aim of the laser scanning was to qualitatively validate ore movement during a voyage. From
these scans it is estimated that the stow height decreases by about 0.6 m from an initial stow height of
14 m. This represents approximately 4% volume reduction (due to compaction, moisture loss or minor
redistribution processes) during the course of a voyage.
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Figure 105: Brazilian cargo laser scan
4.3.2
Free water
During a voyage free water drains from the Brazilian iron ore fines cargo. Figure 106 shows the
material in the hold after loading and before discharge. Water in the corners of the hold can be seen.
Figure 106: Material in hold of Capesize bulk carrier before and after voyage
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4.3.3
Bilge Data
Free water is able to move to the bilge well inlets during the voyage and is pumped from the bilges at
regular intervals. Figure 107 shows an example from laser scanning where water is seen at the bilge
inlet.
Figure 107: Laser scan of cargo stow at the end of the voyage
Bilge pumping indicates that around 1% of cargo moisture (absolute percent change) is removed
during a voyage, for one Brazilian iron ore product. Another Brazilian iron product sees a reduction in
moisture of approximately 0.1%. An example of the daily amount of water pumped from the bilges is
provided in Figure 108. Material ‘A’ has about 60 m3 of water pumped per day and Material ‘B’ has
about 20 m3 of water removed approximately ever three days.
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Figure 108: Daily amount of water pumped from the bilges for materials 'A' and 'B'
4.3.4
Cargo Trimming Practice
Figure 109 shows the case where the cargo is left untrimmed and any surface water settles to either
side of the main stow. The plot shows the impact of reducing the areas of flat stow on the ship’s
stability.
Figure 109: Effect of cargo trimming on ship free surface
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The surface of a liquid in a ship’s hold where the cargo is fully trimmed tends to remain parallel with
the waterline when the ship heels and the centre of gravity of the liquid moves towards the low side of
the hold. This movement in the centre of gravity of the liquid has the effect of raising the ship’s centre
of gravity, thereby reducing the ship’s stability.
The effect of leaving the stow untrimmed can reduce the free surface effect as it greatly reduces the
surface area of the liquid. The amount of this improvement is primarily governed by the width of the
flat area of stow at either side of the cargo hold.
4.4
Comparison and Findings
All TWG companies have collected qualitative (photos, observation reports, inspections) and
quantitative data (laser scanning surveys, bilge pumping) allow understanding of IOF cargo behaviour
during actual voyages.
Laser scanning / survey techniques to monitor cargo movement either at the port of loading and at the
port of discharge or during the voyage or both. The survey data is readily used with ship loading data
to determine bulk density, volume, compaction, surface profile and angle of repose characteristics.
The key comparisons and findings from the cargo observation are;
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Laser scans show quantitatively that the IOF cargo mass does not move significantly within a
hold during voyages.
Cargo volume compaction varies from 0 to 10%, but is typically around 1 to 2%.
Laser scanning / survey provide precise determination of cargo bulk density.
Volumes of pumped bilge water indicate up to 1% moisture reduction (absolute percent
change) during a voyage for Brazilian cargoes. The moisture reduction for Australian IOF is at
least an order of magnitude less.
Bilge pumping data as well as discharge inspections and observations show Australian IOF
have no appearance of free water at discharge. Some Brazilian IOF shows the appearance of
free water during the voyage and can be adequately managed by the pumping of bilges.
Free water effects, where they occur, can be managed by optimising the cargo hold loading
practice as cargo stability can be improved by loading holds to minimise the area where free
water can collect.
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5
CONCLUSIONS AND RECOMMENDATIONS
The marine studies undertaken by the TWG have identified the forces generated in various seas and
conditions, as well as cargo behaviour for IOF from Australia and Brazil. These parameters have
been identified through:
 Vessel motion monitoring
 Cargo observations
 Vessel stability modelling
The parameters are to be used as inputs into the further research being undertaken by the TWG.
A summary of the key findings are as follows:
Vessel Motions and Forces
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Contribution from vibrations associated with engines are negligible.
In respect of rigid body motions, based on vessel motions captured and calculated, only the
vertical and the transverse motions are significant compared to longitudinal motion.
For vertical and transverse motions, accelerations in Handysize vessels are up to twice those
of Capesize vessels.
Capesize vessels have a natural roll period of 10 seconds or 0.1 Hz (based on various RAOs
and response spectra).
Hold 1 (forward hold) experiences the largest accelerations.
Real-world accelerations measured during voyages are typically lower than those predicted by
voyage calculations.
The observed vessel accelerations are less than 1G, typically 0.1G.
Weather routing as an outcome of good seamanship reduces the maximum accelerations
experienced.
Vessel Stability



For Capesize vessels, stability is not compromised unless more than 50% of the cargo mass
has moved significantly.
Handymax and Handysize vessels have a lower reserve stability than Capesize when carrying
heavy density cargoes.
Capesize vessels typically have a metacentric height (GM) many times the value required by
the IMO Rules and the areas under the righting lever curve are typically10 times the rule
requirements
Cargo Observations





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Laser scans show quantitatively that the IOF cargo mass did not move significantly within a
hold during the voyages undertaken.
Cargo volume compaction varies from 0-10%, but is typically around 1-2%.
Laser scanning/survey allows for precise determination (+/-0.5% volumetric) of cargo bulk
density.
Volumes of pumped bilge water indicate up to 1% moisture reduction (absolute percent
change) during a voyage for Brazilian cargoes. The moisture reduction for Australian iron ores
is at least an order of magnitude less.
Bilge pumping data as well as discharge inspections and observations show Australian iron
ores fines have no appearance of free water at discharge. Some Brazilian ores do show the
appearance of free water during the voyage but can be managed by the pumping of bilges.
Limiting trimming to the natural angle of repose impedes the surface impacts of free water.
Research and scientific testing by the TWG to date offer support to the empirical evidence that
problems related to the safe carriage of IOF may be restricted to a certain size and class of vessel.
The stability of Capesize vessels – in which over 90% of global iron ore tonnage is shipped – is not
compromised unless there is a more-than-50% cargo shift. In the case of IOF, cargo observation data
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indicates the cargo mass does not move significantly in these ships and, therefore, its carriage would
not constitute an undue risk.
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6
REFERENCES
BMT; PC Global Wave Statistics - User Manual.
DNV, 2011, “Bulk Carrier’s Safety Study – Intact and Damaged Stability”.
Hogben, N., Dacuhna, N.M.C. and Olliver, G.F. 1986; “Global Wave Statistics”, BMT, London.
IMO, 2009, “International Code on Intact Stability, 2008”, CPI Books London.
IMO, 2011, “Code of Safe Practice for Cargo Stowage and Securing” CPI Books London.
Lloyd’s Register, 2011. “Study of Loading Iron Ore Fines on Very Large Ore Carrier”
Recommended Practice DNV-RP-C205 October 2010 - Appendix B: “Nautic Zones for Estimation of
Long-term Wave Distribution Parameters”
Storhaug, G., 2007, “Experimental investigation of wave induced vibrations and their effect on the
fatigue loading of ships”, Thesis Dept. of Mar. Techn., Norwegian University of Science and
Technology.
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