Education and Training for Boat Designers, Surveyors, Technicians & Marine Professionals – www.westlawn.edu

Westlawn Institute of Marine Technology

Dave Gerr, Director

Westlawn Institute of Marine Technology

c/o Mystic Seaport

PO Box 6000

75 Greenmanville Avenue

Mystic, CT 06355 USA

Tel: 860-572-7900

Fax: 860-572-7939

Email: dgerr@westlawn.edu

Web: www.westlawn.edu

Some Useful References

Nature of Boats: Comprehensive coverage of all aspects of boat design, construction and behavior. Easy read. Non technical.

Boat Mechanical Systems Handbook: Straightforward reference on all aspects of boat systems engineering.

Elements of Boat Strength: Easy to use and comprehensive reference for evaluating and calculating boat structures.

The Problem

a) Numerous small commercial passenger vessels operate on inland waters outside the jurisdiction of the U.S. Coast Guard and the Code of Federal Regulations (CFR) governing such vessels under 46 CFR.

b) There is currently no generally recognized stability standard applicable to such inland commercial vessels.

c) The states seldom have personnel trained to apply 46 CFR stability requirements or assess the safety of a boat with regard to stability.

d) Lack of standards and lack of trained personnel leaves a gap in public safety for commercial passenger vessels operating on inland waters.

There are Boats . . .

Some boat’s at least are pretty obviously properly designed and built . . .

Imagine 57-Foot Voyaging Motorcruiser

Belle Marie/Summer Kyle 42-Foot Shoal-Draft, Beachable Motorcruiser

Kestrel 76-Foot Shoal-Draft, Beachable Motoryacht

??And Then There Are . . .

150 Passengers?

Safe? How Many Passengers?

Stability Standard Must Apply To All

Regardless of outward appearance, it’s still necessary to ensure ALL boats meet basic

stability requirements.

Insufficient Stability Can Be Deadly!!

Ethan Allen 40 ft.

Fiberglass boat, on

Lake George, NY

Ethan Allen Passenger Deck

Ethan Allen Capsize

On October 2, 2005, the New York State certificated vessel Ethan Allen capsized on Lake George, NY.

a) The operator and 47 passengers were aboard.

b) 20 passengers died.

c) 3 passengers suffered serious injury.

d) 6 passengers suffered minor injuries.

e) The operator and 18 passengers survived without injury.

The weather was good and conditions on the lake were calm with very light winds.

Animation of Ethan Allen Capsize

Animation: JMS Naval Architects & Salvage Engineers - www.jmsnet.com

Ethan Allen After Capsize

NTSB Report - Cause of Ethan Allen Capsize

a) An old (1976) Certificate Of Inspection (COI), which permitted 48 passengers, was accepted by the state without a new stability test.

b) Modifications had been made to the vessel but were not reported to the state.

c) Post accident stability tests indicated that the vessel had a high center of gravity (CG) and marginal metacentric height (GM).

d) The boat had a 2-degree list to port, prior to the capsize to port, and was down by the bow by almost a foot! This reduced the waterplane moment of inertia and so further reduced the initial stability.

e) The capsize was caused by INSUFFICIENT STABILTY.

Lady D Water Taxi

36 ft. LOA, 8 ft. Beam, Pontoon Water Taxi

Lady D Capsize

On March 6, 2004, the inspected passenger vessel (a pontoon water taxi) Lady D capsized in Baltimore harbor.

a) 3 crew and 23 passengers were aboard.

b) 5 passengers died.

c) 4 passengers suffered serious injury.

d) 12 passengers suffered minor injuries.

The weather was poor, with rain, developing strong winds and nearby thunderstorms.

Lady D Capsized

NTSB Report - Cause of the Lady D Capsize

a) The sister ship used for stability assessment in 1999, was incorrectly tested using methods applicable to monohulls not to pontoon boats.

b) Test weight had not been moved as far outboard as possible in the test.

c) The USCG granted incorrect sister-vessel status to the Lady D based on the incorrect stability tests.

d) Passenger weight for the stability tests was based on 140 lb./passenger, per regulations, but average passenger weight was 168 lb. at the time of the capsize.

e) Correctly calculated capacity should have been 14 persons total, not 25.

f) The capsize was caused by INSUFFICIENT STABILTY.

SCItantic 90-ft. Stern Wheel Passenger Vessel

SCItantic Capsize

On July 7, 1984, the passenger vessel SCItantic (a 90-foot stern wheeler) capsized on the Tennessee River, near the Redstone Arsenal, in Alabama.

a)3 crew and 15 passengers were aboard.

b)11 passengers died.

c)7 individuals (3 crew and 4 passengers) escaped with little or minor injuries.

The forecast was for the possibility of typical afternoon summer thunderstorms. After leaving the dock, a severe thunderstorm warning was broadcast. By 11:03, winds of 38 knots were reported, and a local downburst/microburst with 70 knot winds then occurred, striking SCItantic broadside.

NTSB Report - Cause of the SCItantic Capsize

a) The vessel’s GM exceeded USCG requirements under CFR 170.170.

b) The vessel was not of “usual proportions,” however, and so should probably have been require to also meet 170.173.

c) The high sided vessel didn’t have sufficient reserve righting energy to withstand 70 knot beam winds.

d) The capsize was caused by unusually high winds on a boat with very high cabin sides.

CRF 170.173 for Vessels of Unusual Form

a) Plot curve of righting arms against curve of heeling arms

b) Crossing point (point of steady heel) not more than 10° (15°-20 sail°)

c) Height of RM curve at steady heel no more than 60% of maximum RM

d) Residual righting energy (Area A) not less than 140% if Area A2

NTSB Report - Cause of the SCItantic Capsize

a) The vessel’s GM exceeded USCG requirements under CFR 170.170.

b) The vessel was not of “usual proportions,” however, and so should probably have been require to also meet 170.173.

c) The high sided vessel didn’t have sufficient reserve righting energy to withstand 70 knot beam winds.

d) The capsize was caused by unusually high winds on a boat with very high cabin sides.

Insufficient Stability Can Show UpImmediately in Severe Cases

Home designed and home built boat of all steel.

Insufficient Stability Can Show UpImmediately in Severe Cases - 2

As Launching Progressed Something Was Very Wrong!

Insufficient Stability Can Show UpImmediately in Severe Cases - 3

The Boat Had Insufficient Displacement & Was Severely Down by the Stern

Insufficient Stability Can Show UpImmediately in Severe Cases - 4

The Boat Was Listing to Port and in Danger of Capsizing in Calm Water Right at the Dock!

Metacentric Height (GM) and Heeled Center of Buoyancy (CB)

Metacentric Height (GM) and Righting Arm (GZ)

Solution – Part 1Create an Applicable Inland Stability Rule that Will:

a) Conform with the general principles and requirements of 46 CFR Simplified Stability, and/or to ABYC standards for pontoon boats, or other existing stability standards as applicable and appropriate.

b) Be as direct and straightforward to read and interpret as possible.

c) Apply only to vessels carrying 149 passengers or less. (Vessels carrying more passengers will be required hire a qualified naval architect, small-craft designer, or marine surveyor to conduct full stability tests under 46 CFR, and present documentary proof of compliance with 46 CFR to the appropriate state regulatory agency to operate in the state.)

d) Be applicable to monohull powerboats, multihull powerboats, pontoon powerboats, monohull sailboats, and multihull sailboats. (Pontoon sailboats will not qualify.)

Operating Procedure

a) Designated, approved state personnel will act as inspectors to conduct the review, inspection, and tests required to pass stability requirements.

b) Upon a vessel’s passage of stability requirements, the state will issue a license or permit to operate while carrying up to the approved number of passengers.

c) The license or permit will be good for a limited period (recommend five years) at which time it must be renewed.

d) The license or permit will also specifically state that it is void if any alterations or additions are made to the vessel.

e) In the event of such alterations or additions, a new ISS will be required for a new license or permit.

Stability Rule Name and Availability

The rule will be called:

The Inland Stability Standard or ISSa) The complete ISS document will be published in

PDF format, available at no cost to for download from the Westlawn Institute website.

b) Any state or local agency or organization, any corporation, or any individual may download and post the ISS PDF document on their website, print it out, or distribute it at will.

c) The ISS document will state that it is void if altered in any way and must be presented in full.

Solution – Part 2Create Distance-Learning

ISS Inspector Training Program:

a) Create a training program—delivered entirely through distance learning—for the personnel who will be conducting the review, inspection, and tests required to pass ISS.

b) The course will be supplied and taught by the Westlawn Institute of Marine Technology.

The Training Program Will:

a) Familiarize inspectors with the need for and meaning of stability requirements and testing.

b) Familiarize inspectors with the overall ISS process, approach, and paperwork.

c) Familiarize inspectors with the terminology used in ISS and its meaning.

d) Review the complete ISS process step by step.

e) Test inspectors knowledge of ISS with an integral series of examinations, including a final exam representing a complete ISS test.

f) Award a certificate to graduating students attesting to their successful qualification as an ISS Inspector.

About the Westlawn Institute of Marine Technology

a) Founded 1930 — 80 years this January.

b) Has trained more practicing boat designers than any other school in the world.

c) Nationally accredited by DETC, in Washington DC.

d) State approved by the CT Department of Higher Education.

e) Recognized by the US Dept. of Education and by the Council for Higher Education Accreditation.

f) Was formerly owned by NMMA.

g) For the past 6 years part of ABYC.

h) 100% of all courses have always been taught via distance learning.

Boats Designed by Westlawn Alumni

More Boats Designed by Westlawn Alumni

Still More Boats Designed by Westlawn Alumni

The Two Fundamental Stability Criteria

The two primary stability criteria to be met are:

1)Wind Heel: That the boat will not heel more than between one-quarter to one-half of freeboard, but never more than 14 degrees in the strongest average beam wind it is likely to experience. This is based on CFR (Code of Federal Regulations) 170.170, often termed “GM Weather.”

2)Passenger Heel: That the boat will not heel more than between one-quarter to one-half of freeboard (more later), but never more than 14 degrees with two thirds of the normal passengers and crew permitted aboard standing on one side or along the rail on one side of the boat. This is based on, CFR 171.050, often called “Passenger Heel.”

Wind Heel

a) For powerboats, use a multiplier in pounds per square foot of wind pressure for the appropriate maximum average wind speed the boat is likely to experience.

b) Take the complete area of the profile of the boat. The designer finds the full area of this in outline including all: stanchions, rails, lee cloths, davits, radar masts, and so on. Also the designer finds the center of the area (CE) above the waterline.

c) Next, the designer locates the center of the lateral plane (CLP) of the hull underbody. Measure the distance it is down from the waterline. This can be estimated as 50% of draft on powerboats.

d) Add the distance WL to CLP to the distance WL to CE to find the total heeling arm HA.

e) Enter this in the powerboat wind-heel formula. The answer should be one quarter to one half freeboard or no more than 14 degrees or less depending on whether it’s an open boat, or a boat with a cockpit, or a flush-deck boat with no cockpit at all.

f) If the resulting heel angle is greater, you must either reduce the “sail” area of the boat’s profile, increase beam, or lower the center of gravity, or some combination of these.

Wind Heel Example Boat

27 Foot Cruiser Inboard Profile

Determine Allowable Heel/Immersion

a) For a flush-deck boat with no cockpit or well deck, the maximum heel is 1/2 the freeboard or 14 degrees, whichever is less.

b) For a completely open boat with a “cockpit” the full length, the maximum heel is 1/4 the freeboard or 14 degrees, whichever is less.

c) Most contemporary boats are largely flush decked but have a cockpit (or a well deck) of some form. For such craft, the maximum heel is somewhere between 1/2 and 1/4 freeboard, or 14 degrees, whichever is less.

Determine Allowable Heel/Immersion 2

The amount of heeled freeboard allowed is determined by the following formula (from CFR 178.330):

For exposed waters:

For protected waters:

Where:immersion = maximum allowable immersion due to heel, ft.f = lowest or minimum freeboard, ft.LOD = length on deck, ft.cl = cockpit length, ft.

immersion = f x ((2 x LOD) - (1.5 x cl))

4 x LOD

immersion = f x (2 x LOD) - cl

4 x LOD

Allowable Heel/Immersion for the 27-Foot Cruiser

LOD is not the same as LOA. LOD is the length of the deck itself and is almost always less than LOA. For our 27-foot cruiser it is 26.8 feet, not the LOA of 27.5 feet, see drawing.

Using the formula for maximum allowable immersion, for our 27-foot motorcruiser, which will operate on exposed waters:

3 ft. freeboard x ((2 x 26.8 ft.) - (1.5 x 8.9 ft.))4 x 26.8 ft.

= 1.1 ft. allowalbe immersion

Understanding the Allowable Immersion Results

a) From the sections, the lowest freeboard happens to be at the transom on this boat. This is 3 feet minimum freeboard.

b) The immersion to the 14-degree heeled waterline is 0.9 feet, which is well under half the lowest freeboard (1.5 ft.) and also is under the maximum allowable immersion for this boat of 1.1 feet allowing for the cockpit.

c) Accordingly, we use the 14-degree heel angle as maximum allowable.

d) If the heeled waterline, at 14 degrees, was higher than half the freeboard or if the immersion depth was greater than 1.1, we would have to find a lower heel angle until we had a heel angle that met all criteria.

Calculating the Heel Angle from Wind Pressure

The heel angle from the wind pressure can be found from:

Heel angle, degrees = P x 57.3 x Profile Area x Heeling Arm ÷ GM x Disp.

Where:Heel angle = degrees of heelP = wind pressure for the selected wind speed, lb./sq.ft.Profile Area = area of the profile of the boat above the waterline, sq.ft.Heeling Arm = distance from center of lateral plane of the underbody to the center of effort of the profile area, ft.GM = metacentric height, ft.Disp. = displacement, lb.

Wind Pressures for Wind-Heel Calculation

Use wind pressures (P) as follow for the intended boat use:

Ocean crossing (50 knots wind) = 13.2 lb./sq.ft.

Coastwise ocean (45 knots wind) = 10.7 lb./sq.ft.

Partially protected waters such as lakes, bays, and harbors (40 knots wind) = 8.5 lb./sq.ft.

Protected waters such as rivers, inland lakes, and sheltered harbors (35 knots wind) = 6.5 lb./sq.ft.

Note: For the U.S. Great Lakes, use coastwise ocean for summer service and ocean crossing for winter service.

Martin’s Wind-Pressure Formula

Wind pressure for a given wind speed is found from Martin’s formula which is:

P = 0.004 x mph2

or

P = 0.0053 x kts2

Where:P = wind pressure, lb./sq.ft.mph = wind speed in miles per hourkts = wind speed in knots

27-Foot Cruiser Wind Heel Area

2.63 ft. + 0.66 ft. = 3.29 ft. HA (heeling arm)

27-Foot Cruiser Wind Heel Calculation

Though we’re discussing inland boats, this is rugged little cruiser intended for venturing anywhere along the coast and possibly some offshore fishing, so the wind pressure (P) should be based on 45 knots wind, or 10.7 lb./sq.ft.

Accordingly:

Heel angle = 10.7 lb./sq.ft. x 57.3 x 125.3 sq.ft. Profile Area x 3.29 ft. HA ÷ 3.85 ft. GM x 6,900 Disp.

Heel angle = 9.5 degrees.

This is well under the 14 degrees we found was allowable and indicates that this boat is is acceptable with regard to wind-heel stability.

Passenger Heel

a) Passenger heel determines how far the boat will heel with the passengers moved to one side of the boat.

b) The U.S. Coast Guard formula for passenger heel uses 140 pounds per person, assuming a mix of men, women, and children. (Other rules from the CFR use as much as 165 pounds.)

c) These weights were settled on decades ago when the U.S. population was physically smaller.

d) Over the last few years, there have been a few capsizing incidents where it became apparent that the average weight of the passengers aboard was well over 140 pounds.

e) In May 2006, the U.S. Coast Guard issued voluntary guidelines for owners and operators of small passenger vessels to re-evaluate the passenger capacity for their vessels based on an updated average weight allowance of 185 pounds. This has not yet been officially changed in the CFR.

Calculating Passenger Heel

The angle of heel resulting from moving weights already aboard a boat a given distance is found from:

Where:W = weight moved, lb.d = distance moved, ft.Disp. = boat displacement, lb.GM = metacentric height, ft.arcsin = The arcsin of X is an angle whose sine is X, often notated as sin-1. It is not the same as 1/sine. The arcsin or arc sine can be found quickly on any inexpensive scientific calculator or in any standard spreadsheet program.

Heel angle, degrees = arcsin W lb. x d ft.Disp. lb. x GM ft.

Passengers to One Side of the 27-Foot Cruiser

Passenger Heel for the 27-Foot Cruiser

Say we have total crew of 8. Two thirds of this is 5.28, say, 6.

Six times 185 pounds equals 1,110 pounds shifted to the rail.

Then, for our 27-ft. cruiser passenger heel would be:

Referring back to our earlier calculations for wind heel, we already found that the maximum 14-degree heel was acceptable and so this vessel easily meets passenger-heel criteria.

arcsin 1,110 lb. x 2.8 ft.6,900 Disp. x 3.85 ft GM.

=6.7 degrees passenger heel

USCG/CFR Wind Heel Criteria – “GM Weather”

a) The preceding works out the naval architects calculations.

b) Passenger vessels on the navigable waters of the U.S. need to comply with the CFR exactly.

c) This is CFR 170.170, often termed, “GM Weather.”

CFR 170.170 – “GM Weather”

Where:GM = metacentric height, ft.P = wind pressure in long tons per square foot, tons/ft.2P = 0.005 + (L ÷ 14,200)2, tons/ft.2

for ocean and coastwise service.P = 0.0033 + (L ÷ 14,200)2, tons/ft.2

for partially protected waters such as lakes, bays, and harborsP = 0.0025 + (L ÷ 14,200)2, tons/ft.2

for protected waters such as rivers and harborsL = length between perpendiculars (waterline length for most ordinary boats), ft.A = projected lateral area of boat profile above the waterline, sq.ft.h = vertical distance from center of “A” down to center of underwater area (center of lateral plane), ft.W = weight of vessel (displacement), long tons (tons of 2,240 lb.)T = heel angle = Heel not greater than between one-quarter to one-half of freeboard (as explained earlier regarding cockpit size), but never more than 14 degrees. The amount of heeled freeboard allowed is determined by the formula from CFR 178.330, exactly as discussed earlier.

≥ P x A x hGM W x tanT

“GM Weather” Wind Velocities

The wind velocities in P for the factors 0.005, 0.0033, and 0.0025 are (using Martin’s formula):

46 knots for ocean and coastwise

37 knots for partially protected waters

33 knots for protected waters

The “(L ÷ 14,200)2” factor in the wind-pressure calculation (P) is to increase the wind speed by 0.0458 knots for each foot of boat length.

CFR 171.050 – “Passenger Heel”

Where:GM = metacentric height, ft.N = number of passengersb = distance from the boat’s centerline to the geometric center of the passenger deck, ft.W = weight of vessel (displacement), long tons—tons of 2,240 lb.

The “24 passengers/long ton” makes the following assumptions:

That the average weight of all passengers (a mix of men, women, and children) is 140 pounds each, and that 2/3rds of them move to the side of the vessel, so – 2/3 x 140 lb. = 93.34 lb., and 2,240 lb./long ton ÷ 93.34 lb. = 24 passenger/long ton.

T = heel angle = Heel not greater than between 1/4 to 1/2 of freeboard (as explained earlier regarding cockpit size from CFR178.330), but never more than 14 degrees.

≥ N x bGM 24 passengers/long ton x W x tanT

What’s Needed for ISS (Inland Stability Standard)

a) What we’ve done is review the principles underlying stability requirements and calculations.

b) The procedure has to from a foundation for ISS, but . . .

1) It’s too complicated

2) Real displacement (weight) is often unknown

3) VCG (vertical center of gravity) is unknown

4) GM (metacentric height) is unknown

5) There often is no architect’s lines drawing of the hull available.

Base ISS Primarily on CFR 171.030 “Simplified Stability,” with Reference to 171.170 and 171.050

and ABYC as Appropriate

Procedure:

a) Determine maximum allowable heel

b) Determine passenger heel moment

c) Determine wind heel moment

d) Incline boat with weights to the larger of the moments

e) Check that allowable heel or immersion is not exceeded

a) Maximum Allowable Heel

The amount of heeled freeboard allowed is determined by the following formula (from CFR 178.330):For exposed waters:

For protected waters:

immersion = f x ((2 x LOD) - (1.5 x cl))

4 x LOD

immersion = f x (2 x LOD) - cl

4 x LOD

b) Determine Passenger Heeling Moment

Two thirds of 8 crew = 5.28. Use 6.

Six x 185 lb.= 1,110 lb.

1,110 lb. x 2.8 ft. to one side = 3,080 ft.lb. moment.

c) Determine Wind Heel Moment

2.63 ft. + 0.66 ft. = 3.29 ft. HA (heeling arm)

10.7 lb/sq.ft. wind pressure x 125.3 sq.ft. = 1,341 lb.

1,341 lb. x 3.29 ft. HA = 4,412 ft.lb. moment

d & e) Incline Boat with Weights to theLarger of the Moments

a) Mark hull side with grease pencil at max. immersion.b) Place known weights on deck at specified distance from center

to create maximum moment.c) Check to see that the boat has not immersed beyond the

grease pencil mark or 14 degrees.Wind heel is greatest moment for this boat at 4,412 ft.lb.

Checking Maximum Heel Angle

a) The mark on the side of the hull is maximum immersion relative to freeboard and cockpit length, per CFR 178.330

b) It’s also necessary to check the heel angle itself to ensure that the angle isn’t greater than 14 degrees.

c) Under the CFR, the ASTM Standard Guide for Conducting Stability Test requires the use of pendulums.

46 CFR, ASTM Heel-Angle Measurement ProcedureUnder the CFR, per the ASTM standard, the heel angle must be measured with 3 pendulums set up in buckets to damp out swing. This is complex and cumbersome for use on boats.

ISS Heel-Angle Measure Using Digital LevelsThe CFR/ASTM pendulum method was created decades ago. ISS will move to using 3 digital levels, to speed up and simplify the heel-angle measurement.

Other Considerations in ISS Test

a) Proper scupper drainage, per ABYC H-4 Cockpit Drainage Systems

b) Openings near the waterline or in the hull side

c) Watertight integrity

d) Vessels of unusual form

Other Vessel Types for ISS

This discussion has been for monohull powerboats. Other types of boat to be covered:

a)Monohull sailboats

b)Multihull powerboats

c)Multihull sailboats

d)Pontoon powerboats(ABYC H-35 Powering And Load Capacity Of

Pontoon Boats)

Pontoon sailboats will not be covered

Vessels carrying more than 149 passengers will not be covered.