SNAME Chesapeake Section Meeting
Tips, Tricks and Trips
in
Inclining Experiments
“There’s no charge It’s worth more for my moose to see your family,
Than it is for your family to see my moose”
“Bert & I”, Marshall Dodge
Chris Barry
The opinions expressed are those of the participants
and do not necessarily represent official policy of the United States Coast Guard
SNAME Chesapeake Section Meeting
15 November 2004
1
Why Are We Here – Goals
Projects – Two documents
• Guidance for owners or operators on inclining
experiments; why, how, general instructions
• Tricks, Tips, and Trips – Today’s Event
 Produce a “how to”,“best practice” manual
- Not a new standard
 Supplement to ASTM F1321 / IACS 31
• http://www.iacs.org.uk/_pdf/Rec31.pdf
 Capture hints, wisdom and war stories
 SD-3
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As wide a range of ideas as possible
SNAME Chesapeake Section Meeting
15 November 2004
2
Topics
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Inclining Experiment vs. Stability Test
Proper Prior Preparation Prevents Poor Perfomance
Setting Up
Finding The Waterplane
Pendulums, Weights and Measuring Heel
Recording Data
Tool Kit
Inclining In Air
ANOVA and Accuracy
Safety
Generating The Report – Computer Applications
SNAME Chesapeake Section Meeting
15 November 2004
3
Inclining Experiment vs. Stability Test
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The purpose of an inclining experiment is to use the
hydrostatic properties of the vessel as a means to
measure the weight, and to determine the center of
gravity of the vessel. This information will be used to
perform other calculations subsequently to determine the
vessel’s safe loading and so on.
You don’t “PASS” an inclining experiment.
A stability test (46 CFR 178.310) IS a test of stability –
mainly for small passenger vessels – it simulates an
overturning event.
Results in lots of heel, requires lots of weight
You do pass or fail it on the spot
SNAME Chesapeake Section Meeting
15 November 2004
4
Proper Prior Preparation Prevents
Poor Perfomance
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Owner / Operator Information
• Good Communication Is Important:
Why, What, How, Who
Fluids and Weights Aboard
• Tankage Condition – Inform the operator as early as possible,
especially regarding fuel – it can be very expensive and/or
difficult to off load fuel.
• Modern computer programs can account for partly full tanks – as
long as they don’t burp
• Be clear about extraneous weight, the less aboard, the more
accurate the incline.
Access: Keys, Gas Freeing, Security, etc.
Make up detailed, ship / person specific checklist
Determine lines plan – may require measuring hull
SNAME Chesapeake Section Meeting
15 November 2004
5
Weights
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What will be used ? Do we have enough ?
• Concrete “Ecology Blocks”
• Drums of Water
• Scrap Metal
• People
Certifying the weights – Bring your own scale
How will weights be moved ? Use ship’s gear ?
• Using ship’s gear is OK if it always returns to the
same fixed point.
Watch Out ! – Make sure that there is room to move
weights without risk to persons, equipment
SNAME Chesapeake Section Meeting
15 November 2004
6
Setting Up
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Where are the pendulum stations ?
• Comfortable location, ready access
• Make sure the reader can get out without bumping
the pendulums, make sure the weights won’t hit the
pendulum.
• Adequate overhead height – typically 8’
Weight moves
• Protect the deck
• Mark weight locations, provide hard stops if
possible
• Move multiple weights full beam or fewer to
intermediate stations?
SNAME Chesapeake Section Meeting
15 November 2004
7
Deadweight Survey
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Make up a frame / deck table ahead of time
Prepare good forms
Have a GA to mark up with items
A portable scale can help – a block the same height
doubles the scale capacity & helps determine CG
A tape recorder is a good tool
Take lots of photos
Even better – take a video camera
But don’t forget to write it down
A small bound book to supplement a stack of forms –
get one that fits in a Zip lock bag
SNAME Chesapeake Section Meeting
15 November 2004
8
Finding The Waterplane
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Probably most important source of inaccuracy
Verify / premark freeboard locations if possible
Take multiple freeboards, as many as possible
• Fit linear equation - Measure beam too, for heel
• Remember to compensate for reader weight
Devices for reading freeboards or drafts
• Scale inside / beside a tube with well submerged
hole to suppress wave action
• Tube with hook for the shear
• Tube with a valve to let in water
• Manometer type system
• Flat bob
SNAME Chesapeake Section Meeting
15 November 2004
9
Draft Gages – Variations on a Theme
Basic concept Submerged
hose damps
waves
Drop gage, open valve at
top to let water in – Retrieve
full, or look at mark on scale
Hook to deck PVC pipe with
clear section
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1
1
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3
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1
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Requires Access to Water
Line
SNAME Chesapeake Section Meeting
No Access
Person)
15 November 2004
Apply air
until
bubbles
seen Manometer
shows how
deep
bottom of
bob is
below
surface (One
Required
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Pendulums, and Measuring Heel
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The bucket can move, the scale can’t
Damping motion
• Oil works well, but it’s HAZMAT, and a spill …
• Liquid dish detergent works as well
• Round buckets damp better than rectangular troughs
Water works in a round bucket
• Watch out for natural period match
Marking battens vs. reading numbers
• A mirror behind the scale improves accuracy
• Set the zero off to one side
Electronic levels – set on slope – reads 10X tangent
Water levels for small craft
SNAME Chesapeake Section Meeting
15 November 2004
11
Recording Data
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Take lots of pictures for setup, freeboards,
deadweight survey
• Did I measure from the top or the bottom?
• Did I check that space?
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tape recorder for taking notes
Video Camera – Captures voice, pictures
Take a lap top and reduce the experiment on the
spot
Fill out forms, mark up drawings
BUT write everything down in a notebook as well.
Notebooks don’t have disk crashes
SNAME Chesapeake Section Meeting
15 November 2004
12
Tool Kit
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Buckets, pendulum bobs, pendulum wire (nylon coated
wire leader), washers, nail or knife edge,
scale (weighting), “legal for trade”: ½% of full reading
Battens or angles, scale rulers or caliper,
Notebooks, camera / videocam / tape recorder, pencils
Hygrometers – get the unbreakable plastic ones
Electronic level (set up at control station)
Measuring: tapes, 1 @ 100’, 2 @ 12’, 6’ folding rule,
sounding tape. Put a magnet on 100’ tape.
Forms and checklists
Safety equipment, Float coat: warmth / rain protection
Snacks; water, lunch (saves time, keeps up morale)
SNAME Chesapeake Section Meeting
15 November 2004
13
Inclining In Air
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Suspend vessel from two points
Weight at each point gives displacement, LCG
• Doesn’t require two scales – One scale, one chain
Suspend boat carefully – Baseline level
Prepare drawing ahead with critical measurements
Locate points very carefully – Level with respect to BL
Same as water incline, but metacenter is hoist point
• Hoist point as low as possible (watch load in slings !)
• Move weight to one side – Measure heel
• Heel Measurement: water/electronic level, laser pointer
• Suspending weight over gunwale gets exact CG
SNAME Chesapeake Section Meeting
15 November 2004
14
Vessels With Cranes
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Frequently two problems:
Find vessel lightship
Find crane weight and CG
Triple Incline
• Perform conventional incline
• Swing crane & measure heel
• Raise crane & rerun incline
• Fit linear regression to determine crane weight and CG
Model crane as two or three “booms” in GHS
Main boom, counterweight, load at tip of boom
Coad, “Floating Crane Stability Analysis”
SNAME Philadelphia Section, 11/98
SNAME Chesapeake Section Meeting
15 November 2004
15
Least Squares, ANOVA and Accuracy
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Use Least Squares Regression to establish waterplane, to
determine GMTMMT
• Freeboard = Draft at Origin + Length * Trim
+ Heel * Halfbreadth (optional)
• Tangent = Moment * 1 / GMTMMT + Offset at 0
• Excel: Linest function gives fit and basic stats
Set up in spreadsheet, recalculates automatically
Linear Regression (Data Analysis); ANOVA & Plot
Have to run manually each time
R2 > 0.999 typical for GMTMMT fit
ANOVA gives confidence level for GMT, Draft
SNAME Chesapeake Section Meeting
15 November 2004
16
Safety
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There is a tendency for engineers to shortcut safety in
inclines, shipchecks and similar inspections.
Avoid it! You won’t be the first naval architect to
be badly injured during an incline or shipcheck.
Shipyard may cause delays, etc. because of safety
violations.
Hard hats, safety glasses, appropriate shoes,
lifejackets / cold water protection
Gas free spaces – confined spaces
• Be careful of CO2 fire suppression systems
Slips and falls – be careful, don’t take chances
SNAME Chesapeake Section Meeting
15 November 2004
17
Generating The Report – Computer
Applications
CONDITION 0
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Using GHS
• Input drafts
• Input loads
• Input GMTMMT
(Doesn’t fit momenttangent points)
• Solves for Lightship
Electronic Form CG993:
Spreadsheets, MS Word
Other Special Programs HEC
SNAME Chesapeake Section Meeting
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AS INCLINED CONDITION
DRAFTS FROM CHECK OF SCUPPER HEIGHTS
BASED ON GMTMMT 8770.15; LEAST SQUARES FIT TO POINTS WITH 1 OUTLIER DELETED
DRAFTS used to establish Waterline
Location-----Given------Used-----Error
3.21f
1.895
1.882
0.013
4.67a
1.920
1.956
-0.036
8.95a
2.018
1.995
0.023
Distances in FEET.---Drafts from Baseline---
WEIGHT and DISPLACEMENT STATUS
Baseline draft: 1.912 @ 0.00, 2.129 @ 23.33a
Trim: Aft 0.22/23.33,
Heel: zero
Part------------------------------Weight(LB)----LCG-----TCG-----VCG
LIGHT SHIP
5,139
1.38a
0.00
2.90
INCLINEWHT1
50
0.93a
0.00
4.50
INCLINEWHT2
50
0.93a
0.00
4.50
INCLINEWHT3
50
0.93a
0.00
4.50
INCLINEWHT4
50
0.93a
0.00
4.50
WOODWHT
35
0.93a
0.00
4.25
FORPEND
35
4.67f
0.00
8.38
FORCLAMP
12
4.67f
0.00
4.40
FORSOAP
51
4.67f
0.00
2.60
AFTPEND
37
4.67a
0.00
8.55
AFTCLAMP
12
4.67a
0.00
4.50
AFTSOAP
46
4.67a
0.00
3.67
1
0.17a
0.00
4.75
5,567
1.31a
0.00
SMARTLEVEL
Total Fixed--------->
3.05
Gals.-----SpGr-----Weight(LB)----LCG-----TCG-----VCG------RefHt
FUEL.C
31.9
0.870
Total Weight-------->
232
3.62f
0.00
1.78
5,799
1.11a
0.00
3.00
Displ(LB)----LCB-----TCB-----VCB
HULL
1.010
5,799
1.13a
0.00
1.45
-1.91
-----------------------------------------------------------------------------Righting Arms:
0.00
0.00
HYDROSTATIC PROPERTIES
Trim: Aft 0.22/23.33, No Heel, VCG = 3.05
Critical point output data deleted for space considerations
LCF
Displacement
Buoyancy-Ctr.
Weight/
Moment/
Draft----Weight(LB)----LCB-----VCB-----Inch-----LCF---IN trim----KML-----KMT
1.923
LCF
5,799
Displacement
1.13a
1.45
Buoyancy-Ctr.
585
1.17a
Weight/
749.24
39.2
4.51
Moment/
Draft----Weight(LB)----LCB-----VCB-----Inch-----LCF---IN trim----GML-----GMT
1.923
5,799
1.13a
1.45
585
1.17a
750.29
36.2
1.51
Distances in FEET.-------Specific Gravity = 1.010.-----------Moment in Ft-LB.
Draft is from Baseline.
15 November 2004
Trim is per 23.33Ft
18
Common Errors In Reducing Experiments
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Freeboard to draft conversions calculated wrong, or waterlines
incorrectly calculated.
• Note: This is supposed to be done at the time of the inclining to
make sure the waterline measurement are good.
Lightship displacement used to calculate as-inclined GM versus asinclined displacement.
Free surface correction of tanks applied incorrectly, double counted,
or missed.
Weights to add/subtract incorrectly entered into software program.
Misunderstanding of lightship definition, and what should and
shouldn't be on the vessel in the lightship condition.
Moment/tangent plot incorrectly used to get slope of line, i.e. used
two points instead of all six in regression analysis.
SNAME Chesapeake Section Meeting
15 November 2004
19
Thank You
Comments
PLEASE !
SNAME Chesapeake Section Meeting
15 November 2004
20