Stability Standards and Testing of Commercial Vessels on Inland Waters (ISS)

Westlawn Institute of Marine Technology

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

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 . . .

??

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
Passenger Deck

Ethan Allen
40 ft.
Fiberglass
boat, on
Lake
George, NY

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

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.

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

Insufficient Stability Can Show Up
Immediately in Severe Cases

Home designed and home built boat of all steel.

Immediately in Severe Cases - 2

As Launching Progressed Something Was Very Wrong!


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


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 1
Create 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 ISS
a) 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 2
Create 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.

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:

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

For protected waters:

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

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

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 heel
P = 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 hour
kts = 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:

Heel angle, degrees = arcsin

 W lb. x d ft.  
Disp. lb. x GM ft.

 

Where:
W = weight moved, lb.
d = distance moved, ft.
Disp. = boat displacement, lb.
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.

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:

arcsin

 1,110 lb. x 2.8 ft. 
 =6.7 degrees passenger heel

6,900 Disp. x 3.85 ft GM.


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.

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”

GM ≥ P x A x h
W x tanT
Where:
P = wind pressure in long tons per square foot, tons/ft.2
P = 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 harbors
P = 0.0025 + (L ÷ 14,200)2, tons/ft.2
for protected waters such as rivers and harbors
L = 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.

“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”
GM ≥ Nxb
24 passengers/long ton x W x tanT
Where:
N = number of passengers
b = 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 CFR
178.330), but never more than 14 degrees.

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:

immersion = f x ((2 x LOD) - (1.5 x cl))
4 x LOD
For protected waters:

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 the
Larger 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 Procedure
Under 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 Levels
The 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.

Stability Standards and Testing of Commercial Vessels on Inland Waters (ISS)

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