SEA TRIAL ANALYSIS JIP

Recommended Practice for Speed Trials
Ordered by
Issued by
: STA-Joint Industry Project
Marin, PO Box 28, 6700 AA Wageningen
The Netherlands, www.marin.nl
18200-2-TM issued 12 September 2006 Marin report
Reported by
Approved by :
: H.J.J. van den Boom, G.G.J Mennen and J.B.Verkuyl
STA-JIP Meeting, Wageningen, 4 July 2006
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Recommended Practice for Speed Trials
REVIEW OF TABLES AND FIGURES............................................................................. 3
1 INTRODUCTION ...................................................................................................... 4
2 TRIAL OBJECTIVE................................................................................................... 5
3 PARAMETERS THAT SHOULD BE LOGGED......................................................... 6
3.1
Primary parameters ........................................................................................ 6
3.2
Other associated measurements .................................................................... 6
3.3
General information ........................................................................................ 7
Model test information .............................................................................................. 7
3.4
Important aspects with regard to the measurements ....................................... 8
3.4.1
Ship track and Speed over Ground ..................................................... 8
3.4.2
Torque................................................................................................. 8
3.4.3
Wind measurements ........................................................................... 8
3.4.4
Depth measurement............................................................................ 8
3.4.5
Wave measurements .......................................................................... 9
3.4.6
Density and temperature at the location of the measurements ........... 9
3.4.7
Current ................................................................................................ 9
4 DATA ACQUISITION .............................................................................................. 10
4.1
General data................................................................................................. 10
4.2
Data on each run .......................................................................................... 10
4.3
Automated data acquisition .......................................................................... 11
4.3.1
Minimum data for acquisition system on each run ............................11
4.3.2
Requirements of data acquisition system..........................................11
4.3.3
Location of data acquisition system .................................................. 11
4.4
Manual data acquisition ................................................................................ 12
5 TRIAL PREPARATIONS......................................................................................... 16
5.1
Step1 Installation and Calibrations ................................................................ 16
5.2
Step 2 Trial agenda and pre-trial meeting...................................................... 17
6 TRIAL BOUNDARY CONDITIONS ......................................................................... 18
6.1
Location........................................................................................................ 18
6.2
Wind ............................................................................................................. 18
6.3
Sea State ..................................................................................................... 18
6.4
Water depth.................................................................................................. 19
6.5
Current ......................................................................................................... 19
7 SHIP CONDITION .................................................................................................. 20
7.1
Displacement ............................................................................................... 20
7.2
Trim .............................................................................................................. 20
7.3
Hull & Propeller............................................................................................. 20
8 TRIAL PROCEDURES ........................................................................................... 21
8.1
Trial preparations.......................................................................................... 21
8.2
The trial trajectory ........................................................................................ 21
8.3
Run Duration ................................................................................................ 22
8.4
Trial Direction ............................................................................................... 22
8.5
Steering ........................................................................................................ 22
8.6
Approach...................................................................................................... 22
8.7
No. of Speed runs ........................................................................................ 23
8.8
Test sequence speed trials .......................................................................... 24
9 REPORTING ..........................................................................................................25
9.1
Report Breakdown ........................................................................................ 25
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10
Recommended Practice for Speed Trials
REFERENCES.............................................................................................. 26
NOMENCLATURE ......................................................................................................... 27
APPENDIX I - ALTERNATIVE METHODS FOR MINIMUM WATER DEPTH................ 29
APPENDIX II - GENERAL SHIP AND TRIAL CONDITIONS REPORTED .................... 30
APPENDIX III – SEASTATE AND BEAFORT SCALE ................................................... 31
Tables
Table 1 Primary parameters............................................................................................ 6
Table 2 Other associated measurements ....................................................................... 6
Table 3 General information............................................................................................ 7
Table 4 Indication of required approach length and time .............................................. 23
Figures
Figure 1 Example of a logform ...................................................................................... 12
Figure 2 Sign conventions............................................................................................. 13
Figure 3 Sign convention for wind directions................................................................. 14
Figure 4 Sign convention for wave directions................................................................ 15
Figure 5 Path of ship during typical speed/power manoeuvre....................................... 21
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Recommended Practice for Speed Trials
The Sea Trial Analysis (STA)-JIP is a Joint Industry Project that has reviewed the current standards for the performance and analyses of speed trials together with ship owners.
In close cooperation with the participating companies, comprising 14 leading ship owners and 6 major ship yards, MARIN has developed a Recommended Practice for conducting speed trials. This document outlines the procedure for the performance of the speed trial, which forms the basis for an accurate assessment of the speed of a ship upon delivery by the yard to the owner.
This Recommended Practice comprises: a) The trial parameters that should be logged b) The trial conditions that should not be exceeded during the trial c) The procedures that should be followed during the trial d) The contents of the trial report
The trial procedures are based on best international practice outlined by the ISO
19019, 15016 Ref [1] and the recommendations to the 22 nd and 23 rd ITTC
(International Tank Towing Committee) by the Trials & Monitoring committee, Ref [2 to 8], discussions with the STA-JIP participants and on experience from MARIN.
In the ITTC recommended procedures extensive procedures are given for the preparation of a speed trial and the execution thereof. The ISO procedure gives some guidelines for the boundary conditions that should apply during the speed trial.
Furthermore, the existing procedures often give a good guideline, but are not specific.
The STA-JIP Practice combines the two latest standards and gives a practical overview of the minimum requirements that should be met in order to obtain reliable speed trial results.
Besides issuing the present report, the STA-JIP has also improved the analysis and correction methods for the results of speed trials. These are described in the
“Recommended Analysis of Speed Trials” (Marin Report No. 18200-9-TM) and implemented in the software package QSTAP.
The following companies participated in STA-JIP: CP Offen, ER Schiffahrt, Hapag
Lloyd, Kuwait Oil Tankers, Maersk, NDR-H.Schuldt, NSB, Shell, Teekay, UECC, Vela
Vroon, DSME, Hanjin, HHI, Samsung, STX and Sumitomo. It was decided by the participants that MARIN will issue this Recommended Practice for use by all shipowners and yards worldwide. Participating companies continue in the STA-group to exchange trial experiences and improve the quality of speed trials.
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Recommended Practice for Speed Trials
The primary purpose of speed trials is to determine ship performance in terms of speed, power and propeller revolutions under prescribed ship conditions, and thereby verify the satisfactory attainment of the contractually stipulated ship speed. Ship speed that is realised under the contractually stipulated conditions which usually are no wind, no waves, no current, deep water, and smooth hull and propeller surfaces and for the ship at a contract draught.
Such stipulated conditions cannot normally all be expected during the actual trials. In practice, certain corrections for the environmental conditions have to be considered, as for water depth, wind, waves and current and deviating ship draught. For this purpose during the trials not only the shaft power and ship speed are measured but also relevant ship data and environmental conditions.
All trials procedures and measurements should be conducted in such away that the speed is determined within 0.05 knots and the power within 2%.
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Recommended Practice for Speed Trials
In this chapter an overview is given of the parameters that influence the trial speed. All these parameters should be recorded as accurately as possible.
For this purpose a division has been made between primary and secondary parameters.
For each of the parameters the acceptable measurement methods are given.
Ship Track
Acceptable measurement devices Unit
DGPS [Latitude, Longitude] or [m]
Ground
Shaft Torque or Shaft Power
Shaft RPM
Propeller pitch
Torsion meter with strain gauges, [kNm], [kW]
Calibrated permanent torque sensor.
Power to be calculated from torque and
RPM
Pick-up, laser counter, ship revs counter [Hz, RPM]
Bridge replicator
Water depth
Rudder angle
Ship heading
Relative wind direction
Draughts
Ship echo sounder + nautical charts
Angular potentio meter, string sensor,
Ship rudder repeater
Gyro compass, or DGPS
[m]
[deg]
[deg]
Ship anemometer, external anemometer [m/s], knots, [deg]
[m], [deg] scanner. etc), Wave buoy, Hind cast, observation by multiple observers
Physical observation and / or calibrated draught gauges
[m]
Table 1 Primary parameters
Acceptable measurement device Unit
Ρ [kg/m^3]
Temperature (CDT) sensor
[ºC] temperature
Air temperature
Air pressure
Thermometer
Barometer
[ºC]
[hPa], [mBar]
Table 2 Other associated measurements
Other associated measurements must be carried out at the trial site
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Recommended Practice for Speed Trials
Prior to the trial, the data specified below shall be recorded, based on measurements where relevant:
Hull condition
Last date of cleaning hull
Hull appendages and Rudder
Geometry
Type
Rate of Movement during speed trials
Wind fetch
Height of wind meter above waterline
Frontal wind area
Propeller(s)
Geometry
Pitch
Direction of rotation
Number of blades
Shaft(s)
G modulus Shaft material properties to be provided by yard (shaft supplier data)
Table 3 General information
The quality and accuracy of model tests play a large role in the outcome of full scale trials. Often sea trials are carried out in ballast condition, whereas the contractual condition most often is defined in loaded condition. For the conversion from ballast to loaded the difference between the ballast and loaded model test curves is used.
Therefore an accurate model test and consistent extrapolation method to full scale is required.
For the analysis of the speed trials i.e the correction of rpm, it is required that the model tests data include the results of propeller load variation measurements.
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Recommended Practice for Speed Trials
For the performance of model tests the International Towing Tank Committee (ITTC) recommends the following procedures which are followed by international recognised model test institutes:
• 23 nd
ITTC 2002; Recommended Procedure for Propulsion Tests [ref.4].
With regard to model tests two main items are important:
1) The standard deviation of power obtained from resistance and propulsion tests should be smaller than 2% ;
2) The model test report should give sufficient information to enable a third party institute to check the model test results using the above ITTC procedure or it’s own extrapolation method. This means that in a model test report raw data should be given, correlation coefficients, a detailed description of the extrapolation method used and of course the full scale prediction.
3.4.1 Ship track and Speed over Ground
The speed is to be measured by a global positioning system such as GPS. The GPS system should operate in the Differential mode to ensure sufficient accuracy; i.e. the speed should be measured within 0.05 knots. The position and speed should be monitored and stored continuously.
3.4.2 Torque
Shaft torque should be measured by means of strain gauges on the shaft for which the zero offset is determined just prior to the trial. The measurement system should be certified for measurements on a test shaft with a bias error smaller than 1% so that an overall bias error of smaller than 2% (on board of the actual ship) can be achieved.
Alternative torque measurement devices with a certified accuracy equal to or better than the above figures are acceptable.
The shaft material properties i.e. the G-Modulus as specified by the shaft supplier should be provided by the yard. The shaft diameter used in the power calculation should be derived from the shaft circumference in-situ measured at the location of the torque instrumentation. measurements
The ship’s own sensor, or an external wind meter can be used. The wind meter must be as clear as possible from the superstructure. In the analyses of the measurements the wind data from two consecutive runs at the same power level are combined to eliminate effects due to the ships superstructure. Continuous recording of the wind during each run is recommended. measurement
This can be done by using the ship echo sounder. It is important that the echo sounder is calibrated before the speed run in combination with the check of the depth on the charts and that the vessel draught is taken into account. Continuous recording of water depth is recommended.
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Recommended Practice for Speed Trials
3.4.5 Wave measurements
Preferably the wave height, wave period and direction of waves due to wind and swell should be determined using instruments. Use can be made of wave buoys or instruments onboard the ships such as a wave radar and wave scanner. Although less accurate, wave observations may also be determined from observations by multiple observers, including an experienced captain, supported by hind casting if the expected effect of the seaway is significant.
3.4.6 Density and temperature at the location of the measurements
The local seawater temperature and density at the trial site need to be recorded to enable the calculation of ship’s displacement and corrections with regard to viscosity.
The water temperature should be taken at sea water inlet level. Air temperature and atmospheric pressure should be measured at the trial location using a calibrated thermometer and barometer.
3.4.7 Current
Current speed and direction shall be obtained as part of the evaluation of each run.
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Recommended Practice for Speed Trials
During the speed/power trial obviously accurate recording of the speed and power relationship is of great importance.
Next to this an accurate quantification of the boundary conditions is necessary since the ship’s speed and powering characteristics are extremely sensitive to conditions such as ship and propeller condition, ship displacement, shallow water effects, sea state and wind velocity. Consequently, these factors must be monitored and documented to the greatest extent possible.
During the speed/power trial two types of data acquisition may be used. Automated acquisition by means of a data acquisition system (measurement computer), and information that is noted down by means of a log sheet. The objective must always be to record as many parameters as possible by means of the measurement computer in order to increase the level of accuracy of the trials.
In general, data to be acquired can be divided into general data which is applicable during all speed runs and specific data that is varying throughout every run.
Prior to the trial, the data specified below shall be recorded, based on measurements where relevant:
• Date
• Area trial
• Weather
• Mean water depth in area of trial
• Water temperature and density
• Air
• Height of wind instrument above waterline
• Fore, amidships and aft draughts
• Displacement
• Absolute wind speed and direction by shore based station(s) or as measured directly prior to and after finalising the speed trials while the vessel is still in the water
• Clock time at commencement (UTC)
• Time elapsed over the measured distance
• Course direction / compass heading
• Ship’s speed over the ground
• Ship’s course over ground
• Offset of track
• Propeller
• Propeller shaft torque and/or power
• Propeller pitch in case of CPP
• Relative wind velocity and direction by anemometer
• Mean wave period, significant wave height and direction of waves (Wind Seas)
• Mean wave period, significant wave height and direction of waves (Swell)
• Max. rudder angle
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Recommended Practice for Speed Trials
4.3 Automated data acquisition
The acquisition system must be able to record time histories of the measurements described in chapter 4.3.1 in order to assure quality control and to provide information, that will allow for the development of uncertainty analysis.
4.3.1 Minimum data for acquisition system on each run
An overview of minimum parameters that must be recorded during the speed trial is given below.
• Date
• Run
• Time
• Propeller shaft torque or power
• Propeller rpm
• Ship positional data
• Ship
• Ship’s speed over the ground
• Relative wind direction and relative wind speed
4.3.2 Requirements of data acquisition system
The data acquisition system must be able to :
• Record all available parameters simultaneously on one computer
• Perform a time trace recording of at least 1 Hz. ( Data sampling during a run is typically between 0.2 and 1 samples/second and is dependent on the physical phenomenon being recorded)
• Display time traces of all trial parameters
• Calculating statistics (Mean, min, max, standard deviation)
At the end of each run the data acquisition system should be able to present all recorded time histories to evaluate the quality and consistency of the acquired trial data and be stored for on-line graphical presentation.
Furthermore the acquisition system must be able to present the following statistical values for each of the measured data:
2. Number of samples taken
Filtering of the run data is recommended to avoid “spikes” in the recorded time histories.
ITTC suggests the use of Chauvent’s criterion that provides a ratio of maximum acceptable deviation to precision index as a function of the number of readings, (N).
Readings are automatically rejected from use in the data analysis when they fall outside of the selected mean value bandwidth.
4.3.3 Location of data acquisition system
It is recommended that the data acquisition system is set-up on the bridge.
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Recommended Practice for Speed Trials
For those parameters that can not be acquired automatically by means of the data acquisition system, manual acquisition is required with use of a log sheet
The log sheet is important for two aspects:
1. First of all to complete the dataset
2. Secondly to provide a backup for the automated measurements and give a written overview of the measurements.
It is important that the parameters that are varying in time will be recorded every few minutes so that the average can be determined over the run period.
An example of a log sheet that can be used is given in Figure 1. The sign conventions to be used for wave and wind direction are presented in Figures 2, 3 and 4.
Ships name :
Speed / Power Trials Log Form
Date:
Run
No.
File name
Time
[hh.mm]
Positions
Anemometer
GPS
MQK
Average pos.
Latitude
[deg]
Longitude
[Deg]
X
Heading
[deg]
Depth
[m]
Y Z
Rel. wind speed
[m/s]
[kn]
Direction
[deg]
Rudder angle [deg]
Log
[kn]
Speed
GPS
[kn]
Ship
T fwd
T aft
Displ. m m tons
Waves visual
Height
[m]
Period
[s]
Direction
[deg]
Environment
T air
T water
ρ water
Propeller PS
°C
°C kg/m3
Torque
[kNm]
Power
[kW]
Revs
[RPM]
Shaft outer dia D1 inner dia D2 steel type
Propeller SB mm mm
Torque
[kNm]
Power
[kW]
Revs
[RPM]
Remarks
Figure 1 Example of a logform
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Recommended Practice for Speed Trials
Figure 2 Sign conventions
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Recommended Practice for Speed Trials
Figure 3 Sign convention for wind directions
The wind direction is defined as the direction where the wind is coming from.
0 degrees on the bow and positive to starboard (clockwise).
Input parameters:
Heading: Heading of the ship; compass course [deg]
VAW: Apparent wind speed [knots]
BAWD:
VSM:
Apparent wind direction relative to the bow, ship fixed [deg]
Ship speed over ground [knots]
Computed parameters:
BTWD
VTW
True wind angle in earth system [deg]
True wind speed [knots]
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Recommended Practice for Speed Trials
Figure 4 Sign convention for wave directions
The wave direction is defined as the direction where the waves are coming from.
0 degrees on the bow and positive to starboard (clockwise).
Input parameters:
Heading: Heading of the ship; compass course [deg]
HW13:
MUWAVD
VSM:
Significant wave height [m]
Wave direction relative to the bow [deg]
Ship speed over ground.
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Recommended Practice for Speed Trials
The success of the speed/power trial largely depends on the preparations of the trial. The
ITTC 19019 gives an elaborate description of the actions that should be taken for a good preparation. In this chapter the most important steps are summarized.
Assemble all trials instrumentation in the configuration that will be used on the ship. Test the instrumentation system for malfunctioning instrumentation or any other complications.
Apart from the obvious signals such as shaft torque, rpm and DGPS it is important to check:
6. Propeller pitch port and starboard if available
8. Water depth measuring system
All shipboard signals to be recorded during the trials must be calibrated after the instrumentation installation is completed prior to the trials. For this purpose the sensors should be cycled throughout the full operating range of the system.
This is accomplished by:
• Slewing gyrocompass
• Moving the rudder to different positions
• Changing the propeller pitch
• The shafts will need to be rotated on the turning gear to zero the torsion meter prior to getting underway
The ship’s draught measurement system needs to be verified prior to getting underway for trials, by directly reading all draught marks seawater temperature, specific density and the internal draught system at the same time.
The torque measurements system should be corrected for any zero offset. As part of the pre-trial calibration, the torsion meters zero torque readings should be determined since there is a residual torque in the shaft, which is resting on the line shaft bearings. The shaft is jacked both ahead and astern and the average of the readings noted. The zeroes are set at the midpoint of the torque required to jack each shaft astern. Setting the torque in this manner, means that the measured torque underway includes the torque to overcome any bearing friction. The final torque values used are derived from the drag shaft procedure (ITTC 7.5-04-01-01.4).
Checks of the torque measurement calibration should be made just before and after the speed trials. No difference is allowed between runs.
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Recommended Practice for Speed Trials
As part of the pre-trial calibration for a ship equipped with controllable pitch propellers the following procedures have to be as following:
1. Prior to dock-out the OD mechanism showing the propeller pitch should be checked for zero pitch;
2. Check zero pitch reading in the measurement system against the mechanical reading in the OD box should be made;
3. Determine the maximum ahead pitch, design pitch, and maximum astern pitch and then adjust the ship indicators to reflect the measurement. Determine the corrections to account for changes in pitch due to shaft compression as thrust increases and temperature effects on the propeller pitch control rod.
4. Verify the weight of the propulsor and hub from the manufacturer’s specifications for use in making thrust measurement corrections
An important deliverable of this stage will be a document describing the test set-up, and the calibrations including evidence of the calibrations that have been carried out.
It is important to note that there are two stages to consider in performing instrumentation checks; the pre-trial check procedures and the post trial check to verify the calibration results.
Before departing, a pre-trial meeting should be held to fix the speed trial program and trial agenda.
During the meeting two items should be addressed.
• Approval of the trial agenda
• Approval of the correction methods and procedures that will be used to calculate the trial speed
The trial agenda is a document prepared by the yard, outlining the scope of a particular
Speed/Power trial. This document contains the procedures on how to conduct the trial and table(s) portraying the runs to be conducted. It outlines the particular responsibilities of the
Trial Director, Trials team, Ship’s crew/ Shipbuilder, and the Owner’s representative.
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Recommended Practice for Speed Trials
During the trial there are many conditions that deviate from the contract condition. The objective during the trial is to keep the number of influencing factors as limited as possible.
This is important since although there are correction methods to correct for certain deviations from the contract condition, these methods are only valid up to certain limits.
In order to arrive at reliable speed trial results the boundary conditions should not exceed the values given in this chapter.
6.1 Location
High wind and sea state can force the use of excessive rudder deflections to maintain heading, and thus cause excessive fluctuations in shaft torque, shaft speed and ship speed.
The speed trial should be conducted in a location where the environmental conditions are constant and have only a small possible impact on the vessel in order to avoid unexpected environmental effects in the trial results.
This means that the speed trial range should be located in a sheltered body of water
(i.e. limited wind, waves and current). Furthermore the operational area should be free from substantial small boat traffic and commercial traffic.
6.2 Wind
During the trial wind speeds should not be higher than:
Beaufort number 6 1 , for vessels with a Lpp ≥ 100 m, or
Beaufort number 5, for vessel with a Lpp < 100 m
The total wave height, H , which is the sum of significant wave heights of sea H
1/ 3
and swell H s 1/ 3
, shall satisfy the following:
L pp
>100 m: the lower value of H ≤ 0.015 L pp
or maximum 4 m.
L pp
≤ 100 m: H ≤ 1.5 m
Where: H
=
H 2
1/ 3
+
H 2 s 1/ 3
In addition to the above limitations, it is required that when the significant wave height
H exceeds 3.0 m (for vessels with L pp
>200 m) , the actual wave spectrum encountered during the trial should be measured accurately i.e. the significant wave height should be known within 5%.
1
The Beaufort scale is given in appendix III
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Recommended Practice for Speed Trials
There are correction methods that compensate for shallow water; however it is better to avoid the corrections by the choice of the trial location.
An acceptable minimum water depth for the trials where data do not need to be corrected for shallow water can be calculated using:
Use of the larger of the 2 values obtained from the two equations. h
>
3 B T and h
=
2.75
V s
2 g
Furthermore significant variations in the bottom contours should be avoided
6.5 Current
Areas with known large current variations should be avoided.
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Recommended Practice for Speed Trials
7.1 Displacement
The ship’s displacement should be within 2% difference of the actual required displacement. If model test results are used for the analysis of the speed trials, the displacement of the vessel during the trials should be within 2% of the displacement used in the model tests for the trial draught.
Draft, trim and displacement of the trials must be obtained by averaging the ship draft mark readings. The ship should be brought into a loading condition that is as close as possible to contract condition and/or the condition at which model tests have been carried out. Usually model test results at different draughts are used for the conversion from the trial draught to the actual contract draught.
The loading condition must be confirmed at zero forward speed. Draft, trim and displacement must be obtained at the beginning and at the end of the trial. This may be accomplished by a second draft reading, by use of the calibrated draught gauging system or by use of a loading computer. For this purpose the draught gauging system should be tested and calibrated prior to the trials in port by direct draft readings both port and starboard in conjunction with the loading computer. The trial team will verify the accuracy of the draught gauging system prior to the Speed/Power trials.
Displacement must be derived from the hydrostatic data by using the draft data and the density of the water.
7.2 Trim
Trim shall be maintained within very narrow limits. For the even keel condition the trim shall be less than 1.0% of the mid-ships draught. For the trimmed trial condition, the trim shall be within 3% of the trim tested at model scale and the immergence of the bulbous bow should be equal to the model test condition.
The ship should have a clean hull and propeller for the sea trial. Hull roughness and marine growth can increase the resistance of the ship significantly but are not corrected for in speed trials. Therefore it is recommended that the hull and propeller are cleaned just prior to the sea trials.
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Recommended Practice for Speed Trials
On the day of the speed trial and during the speed trial a number of prerequisites should be met in order to arrive at reliable trial results. In this chapter an overview is given of the minimum requirements.
Prior to the speed trials the following items should be recorded.
• Weather
• Water temperature and density
• Air temperature and air pressure
• Fore, amidships and aft draughts
• Displacement
The schedule for the speed trials should be arranged such that the trials around the contract speed/power settings are conducted at daylight, to ensure a clear observation of the wave conditions during these runs.
Furthermore, it is important to check that the engine plant line up during the speed trial is consistent with normal ship operations.
Before the actual start of the speed trials, the following actions should be conducted when the vessel is stopped in the water (within the schedule of the trials):
1. draught reading as described in section 7.1
2. measurement of absolute wind speed and direction
3. zero setting of shaft torque meter.
For confirmation, the above actions have to be repeated during the first stop of the vessel in the water (within the trials schedule) after completion of the speed trials.
The trial runs need to be conducted over the same ground area. For each base course, each trial run will be commenced (COMEX) at the same place (within reason).
Figure 5 Path of ship during typical speed/power manoeuvre
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Recommended Practice for Speed Trials
Modified Williamson turns will be executed between each run to return the ship to the reciprocal baseline and to the same ground area, in which the previous run was conducted. This procedure is used to avoid the possibility of coming across different magnitudes of seawater or wind due to large changes in the geographical position of the ship. Engine throttles should not be moved during this evolution so that the ship’s machinery plant will steady out sooner. The rudder angle used in this manoeuvre should be such that ship speed and time loss will be minimised.
The trial duration should be between 5 and 10 minutes in order to accommodate a speed/power measurement within the required accuracy. The following minimum run lengths should be observed: for speeds of 18 knots and above: for speeds below 18 knots:
3 nm
2 nm.
8.4 Trial Direction
For large vessels it is strongly recommended to carry out the speed runs with and against the dominant wave direction, because good correction methods exist for wind from different wind angles, but not for waves.
Once the heading for the trial is fixed, and the reciprocal heading for the return run, the selected tracks should be maintained very precisely throughout the trial. It is imperative that extremely tight control is exercised during the conduct of the trials to minimize as many variables as possible that could unduly influence the speed power relation.
An experienced helmsman will be required to maintain heading during each trial run. He should use minimum rudder angles commensurate with maintaining a steady heading.
During the run, the single amplitude of variation of rudder angles shall be within 3 degrees. Furthermore the measured counter rudder to maintain a straight course shall be within 5 degrees.
8.6 Approach
The trial approach should be long enough to ensure a steady state ship condition prior to commencement (COMEX) of each run. During the approach run the ship should be kept on course with minimum rudder not to retard the vessel.
No fixed approach distance can be given. To verify that the vessel reached the steady ship condition the measured values of shaft r/min, shaft torque and ship speed in the control position should be used. The condition is considered “Steady” when the ordered r/min(s), shaft torque (kNm) and the ship speed (kn) are steady.
Table 4 provides an indication of approach lengths and corresponding times for various ship speeds.
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Size of ship
[DWT]
50,000
100,000
250,000
Recommended Practice for Speed Trials
Approach distance [nm]
4 - 5
5 - 7
8 – 10
Approach time [min]
15 knots
20
26
40
20 knots
15
20
30
45
Table 4 Indication of required approach length and time
25 knots
12
16
24
36
8.7 No. of Speed runs
All speed trials shall be carried out using double runs, i.e. each run should be followed by a return run in the exact opposite direction performed with the same engine settings.
To determine the speed-power curve for the first of a series ship, a minimum number of 4
(four) double runs at 3 (three) different power settings are required. These runs comprise:
• 2 (two) double runs at the same power setting around the contract power
• double runs at two other power settings between 65% and 100% MCR.
The 2 (two) double runs around contract power are required to compensate for tidal currents and should be conducted at daylight to enable a clear observation of the wave conditions.
If the results of the speed trials of the first of a series are acceptable, sister ships in that series may be subjected to a reduced speed trial program. For identical sister ships it is sufficient to conduct 2 (two) double runs at the same power setting around the contract power in order to confirm the level of the speed/power curve obtained by the first vessel.
In case it is proven and accepted by both parties that the maximum current speed in the speed trial area at the time of the speed trials is less than 0.2 (zero point two) knots, the two double runs required for sister ships can be reduced to one double run.
For both the first of a series and following ships, one additional double run should be conducted for each power setting in case:
• Strong variations in current can be expected;
• Wave height is around the limiting conditions and significant wave induced motions are observed;
• A long duration is required for the whole speed trials, the time and sequence between all the speed runs and the presence of time gaps between the runs;
23

8
9
6
7
3
4
Recommended Practice for Speed Trials
8.8 Test sequence speed trials
1 Check displacement by draught reading fore, amidships at two sides and aft, prior to the speed trials in the trial area; Check zero setting of the torque measurement, measure the absolute wind velocity and direction. (All data collected with the ship stopped in the water);
2 Measurement of specific mass of sea water prior to the trials in the trial area;
5
Weather observations (measurements of air and sea water temperature, relative wind speed and direction);
Fixing of measuring course against direction of seaway;
Navigating through the approach distance on direct course;
Prepare all measurements to start (3 min. in advance of measurement);
Start speed run. Control levers should remain unchanged, maximum rudder angle shall not be more than 3 deg. port and starboard. After agreed duration (5 to 10 minutes) or distance (2 to 3 nm) stop speed run;
Turn ship with small rudder angles to navigate the counter run at the same geographical location as the first run;
Repeat steps 5 to 8.
24

Recommended Practice for Speed Trials
In the trial report an overview is given of the trial conditions and results plus all corrections necessary to arrive at the contractual speed.
The trial report should contain all relevant information to carry out all data analyses.
The report should be written in such a way that all results can be reprocessed.
The trial report should contain the following sections
(i) Trial Report Summary this should comprise details of
(aa) Ship particulars (including trial draughts and displacement)
(ab) Propeller Details
(ac) Engine Data
(ad) Details of Appendages and Rudder
(ii) Contract conditions including contract speed, power, displacement.
(iii) Description of Instrumentation this will describe the instrument set-up, calibration procedure, Data Acquisition interfacing details, Location of sensors (e.g. wind meter), etc.
(iv) Description of Trial Site. this will give information on geography, distance from land, water depth, Air temperature, Water temperature, water density etc
(v) Environment Parameters this will list out the measured/estimated environmental conditions at site during trials such as wave height, wave direction, sea state, Air pressure, Wind direction, Wind velocity etc.
(vi) Trial Agenda this will give a complete and chronological order of the trial programme
(both planned and actual) with specification of duties of different recording/monitoring stations on board
(vii) Trial Results (a) Date (b) Time (c) Run no (d) Ship position (e) Ship's heading (f)
Run duration (g) Average ship speed (h) Average and standard deviation torque (per shaft) (j) Average shaft rpm (per shaft) (k) Average shaft power (per shaft) (m) Average rudder angle (n) Relative wind speed and direction (p) Significant wave height and direction (sea state)
(viii) Correction methods this should contain information about the used correction methods including references, input and output
(ix) Conclusions / Recommendations
25

Recommended Practice for Speed Trials
[1] International standard ISO 15016 and ISO 19019 “Ship and marine technology –
Guidelines for the assessment of speed and power performance by analysis of speed trial data”, First edition 2002-06-15;
[2] ITTC Recommended procedures “Speed/Power Trial preparation”, 7.5-04-01-
01.1, 23 rd ITTC 2002;
[3] ITTC Recommended procedures “Speed/Power Trial Ship Inspection”, 7.5-04-
01-01.2, 23 rd
ITTC 2002;
[4] ITTC Recommended procedures “Speed/Power Hull and Propulsor Survey”,
7.5-04-01-01.3, 23 rd
ITTC 2002;
[5] ITTC Recommended procedures “Speed/Power Trial Instrumentation and
Calibration”, 7.5-04-01-01.4, 23 rd ITTC 2002;
[6] ITTC Recommended procedures “Speed/Power Trial Conditions”, 7.5-04-01-
01.5, 23 rd ITTC 2002;
[7] ITTC Recommended procedures “Speed/Power Trial Conduct”, 7.5-04-01-01.6,
23 rd
ITTC 2002;
[8] The Specialist Committee on Speed and Powering Trials. Final report and recommendations to the 23 rd
ITTC, page 314-367;
26

Recommended Practice for Speed Trials
C
WL
A
TRANS
A
BULB
H
BULB
S w
S
APP
K
APP
K
YY
L
ABDA
H
ANEMO
A
TRAN
List of Symbols
L wl
L pp
∇
Δ
Length between perpendiculars
Displaced volume
[m]
[m]
[m 3 ]
Displacement [t]
B Breadth [m]
D Depth
T
T
L aft fwd
CB
C
M
Draught at aft perpendicular
Draught at forward perpendicular
Longitudinal centre of buoyancy forward of midship
[m]
[m]
[m]
Prismatic waterline coefficient
Submerged area transom
Area bulb on FPP
Height centre of ABULB above base line
Wetted surface appendages
Form factor for appendages
Longitudinal radius of gyration
% of LPP
[-]
[-]
[m
[m
2
2
]
]
[m]
[m
[m
2
2
]
]
[-]
Height anemo meter above water
Transverse area above water
% of LPP
[-]
[m]
[m
2
]
NCR
MCR
RPMMCR
RPMNCR
Nominal continuous rating
Maximum continuous Rating
RPM at MCR
RPM at NCR
SEA
MAR
RPM
MAR
Sea margin in percentage NCR
RPM margin in percent RPM at NCR
ETA
S
Shaft
CA Trial allowance coefficient*10^5
K
FAC
AD
HULL
Hull roughness * 10 ^ 6
N
PROP
I
Z
Number of propeller blades
D
PROP
A
E
/A
O
Blade area ratio
KB clear
A
AM
BN
REF
Reference Beaufort number
[kW]
[kW]
[rpm]
[rpm]
[%]
[%]
[-]
[-]
[-]
[-]
[-]
[-]
[m]
[-]
[-]
[m]
[-]
[-]
27

Recommended Practice for Speed Trials
TEMP
TEMP
D
H
B
T
ISPLS
RUD
RUD
RUD
S
AS
Reference sea water temperature
Reference air temperature
Mean height of Rudder
Mean chord of rudder
Maximum thickness of rudder
[ ° C]
[ ° C]
[m 3 ]
[m]
[m]
[m]
[m]
Heading
BAWD
VSM
MUWAVD
V s
P s
Heading of ship; compass course
Apparent wind direction relative to bow
Ship speed over ground
Wave direction relative to bow
[deg]
[kn]
[deg]
[kn]
[m]
[deg]
δ P win
δ V wav
δ V dep
δ P tem
δ P den
δ P dis
δ P rud
δ RPM
Power correction factor for wind ( DPWIN ) [k
Speed correction factor for waves (
Speed correction factor for depth (
DVWAV
DVDEP
) [kn]
) [kn]
Power correction factor for temperature ( DPTEM ) [k
Power correction factor for density (
Power correction factor for displacement (
Power correction factor for rudder angles ( correction factor for RPM ( DRPM
DPDEN ) [k
DPDIS ) [k
DPRUD ) [k
W]
W]
W]
W]
W]
) [-]
V s,c
P s,c
Corrected ship speed (
Corrected ship power (
VSC
PSC
) [kn]
) [kW]
RPM c
Corrected ) [-]
ρ
ρ sea, ref sea
Sea water density according to contract
Sea water density
[ kg / m
[ kg / m
3 ]
3 ]
28

Recommended Practice for Speed Trials
Accepted methods for calculating the minimum water depth for the trials where the data do not need to be corrected for shallow water influences:
SNAME 1973/21 st ITTC Powering Performance Committee d
≥
10 TV /
( )
2 d =
T = trial draft
V =
L = Length between particulars
Sname 1989 from Det Norske Veritas
Nautical Safety- Additional Classes NAUT-A, NAUT-B and NAUT-C, July 1986 h
>
5.0
A m and h
>
0.4
V
2
Use the larger of 2 values obtained from the two equations.
nd
th
h
>
3.0 ( BT ) and h
>
2.75
V g
2
Use the larger of 2 values obtained from the two equations.
29

Recommended Practice for Speed Trials
Ship Hull
Draft
Trim Displacement and load
Hull appendages and Rudder
Geometry, deviation, roughness
Type
Rate of Movement
Propeller
Geometry, deviations, roughness
Pitch
Direction of rotation
Number of blades
Propeller(s)
Geometry, deviations, roughness
Pitch
Direction of rotation
Number of blades
Trial Site
Water depth
Water temperature
Air temperature
Sea State
Specific gravity of water
Environmental conditions
Wind
Waves
Current
Atmospheric pressure
30

Recommended Practice for Speed Trials
SEA STATE SCALE
7
8
9
?
4
5
6
0 Calm-Glassy
1
2
3
Calm-Rippled
Smooth-Wavelet
Slight
Moderate
Rough
Very Rough
High
Very High
Phenomenal
Beyond Belief
0
0 - 0.3
0.3 - 1.7
1.7 - 4
4 - 8
8 - 13
13 - 20
20 - 30
30 - 45 more then 45 more then 90
BEAUFORT WINDSCALE
0
0 - 0.1
0.1 - 0.5
0.5 - 1.25
1.25 - 2.5
2.5 - 4
4 - 6
6 - 9
9 - 14 more then 14 more then
Bft Description
0 Calm
1
2
3
4
5
6
Light
Light
Gentle
Moderate
Fresh
Strong m/s knots km/hr mi/hr
<0.2 < 1 < 1 < 1
0.3 - 1.5
1.6 - 3.3
3.4 - 5.4
5.5 - 7.9
8.0 - 10.7
10.8 - 13.8
1 - 3
4 - 6
7 -10
11 - 16
17 - 21
22 - 27
1 - 5
6 - 11
12 - 19
20 - 28
29 - 38
39 - 49
1 - 3
4 - 7
8 - 12
13 - 18
19 - 24
25 - 31
7
8
Near Gale
Gale
13.9 - 17.1
17.2 - 20.7
28 - 33
34 - 40
50 - 61
62 - 74
32 - 38
39 - 46
9
10
11
Strong Gale
Storm
Violent storm
20.8 - 24.4
24.5 - 28.4
28.5 - 32.6
41 - 47
48 - 55
56 - 63
75 - 88
89 - 102
102 - 117
47 - 54
55 - 63
64 - 74
12 >32.6 >63 >117 >74
© Copyright 2002 KNMI
31

Recommended Practice for Speed Trials
32