ITEA Conference
Salt Lake City
Dr. Brad Christensen
Berea College
Why boats?
 Fun
 Interesting
 Many activities that can be done in the classroom
 Absolutely critical for a world economy
 Full of opportunities for Constraints, Optimization,
and Predictive Analysis
Basic boat dimensions
 LOA
 LWL
 Beam
 Beam WL
 Draft
 Freeboard
 Displacement
length over all
length water line
width
usually 90%-95% of beam
boat hull below the water line
boat hull above the water line
amount of water pushed aside
Displacement vs Planing hulls
 Displacement hulls
 Usually rounded
 Upswept buttock lines aft
 Can be heavy
 Push water out of the way and then allow it to flow back
behind the boat
 Planing hulls
 Usually more flat or square
 Straight buttock lines aft
 Lightweight
 Designed to skim over the water
Displacement
 (Beam WL X draft) X mid section coefficient =
midsection displacement
 (LWL X Midsection displacement) X Prismatic
Coefficient = displacement in cubic feet
 1 cubic foot of water weighs about 64 pounds
Floatation
 How much weight will it take to sink another inch?
 Water plane area
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Multiply water line length (LWL) by water line beam times
prismatic coefficient (.76 for a standard hull)
Water is 5.34 pounds for 1 sq. ft. 1 inch deep
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Light fine ended sailboats
Heavy, full ended sailboats
Fine ended power boats
Full ended planing boats
.68
.71
.74
.80
Center of Buoyancy
 Usually about 55% of LWL from bow
 Can be as much as 65% for some powerboats
 More accurate to make a CB calculator
 Graph displacement at each section of hull
 Connect the points with a fair curve
 Cut out graph and balance on a knife edge
 Balance point is the Center of Buoyancy
Trim
 Square of the water plane area and multiply by 0.35
(for square feet). Divide that number by the water line
beam.
 16 ft by 2 ft kayak
water plane area is 20.8 sq. ft.
 20.8 squared = 424.32
 424.32 times 0.35 = 148.5
 148.5 divided by 2 = 74.25 foot/pounds per inch of trim
 If you placed 74 pounds one foot behind the CB, the
bow would be about 1 inch above the stern
Out of trim
 How much out of trim is still okay?
 About 1% of LWL

1% of 16 ft (192 inches) LWL is about 2 inches
How fast will she go?
 How fast do you need/want to go?
 4 miles per hour rowing
 10 miles per hour sailing
 50 mph is very, very fast on water
 Most skiers do about 30 mph or less
 Most production powerboats operate best at 20-35 mph
 Super high speed boats do between 80-120 mph
 World speed record is 315 mph held by Ken Warbly of
Ohio since the late 1970s
Speed of a displacement hull
 Theoretical Hull speed
 Knots = 1.34 times square root of LWL
 1 knot = 1.15 mph
 Increase LWL will increase hull speed….up to a point
 Increases LWL increases wetted surface which increases
drag
Speed of a planing hull
 Most critical factor in planing boat speed is the power
to weight ratio
 Accurate weight
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Boat
Crew
Supplies
Fuel
 diesel 7.2 lbs/gal
 gasoline 6.1 lbs/gal
Fresh water
 8.4 lbs/gal
Speed of a planing hull
 Accurate power
 Outboards
power measured at prop
 Inboards
figure about 95%
 Engines run continuously at about 60%-70% max so
figure horsepower at about 60%-70% max rating
 Subtract another 4%-6% for friction in the drive train
Speed of a planing hull
 Pounds per horsepower ratio
 5 lbs/hp
80 knots
 10 lbs/hp
60 knots
 15 lbs/hp
50 knots
 20 lbs/hp
42 knots
 25 lbs/hp
37 knots
 30 lbs/hp
33 knots
 35 lbs/hp
31 knots
 40 lbs/hp
29 knots
Fuel Economy
 Diesel engines
 0.055 gallons per horsepower per hour
 100 horsepower engine would use 5.5 gallons per hour
 100 horsepower drives a 2000 pound boat at about 38
mph so the boat gets 6.9 mpg
 Gasoline engines
 0.1 gallons per horsepower per hour
 100 horsepower engine would use 10 gallons per hour
 100 horsepower engine drives a 2000 pound boat at
about 38 mph so the boat gets 3.8 mpg
Speed of a sailboat
 Usually displacement hull so limited by LWL
 Sail area to displacement ratio (power to weight)
 Sail area divided by Displacement (in cubic feet to the
2/3 power) = SA/Disp ratio
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Cruising boats
Performance cruisers
Racing boats
High performance racer
Performance multihulls
16-18
18-20
20-22
22 and up
28 and up
Barge Activities
 Make it float
 Hold a lot of weight for given size
 Make it fast
 Hull shape for best speed given size, weight, and
power
 Make it efficient
 Pay for weight carried but charge for power
 Ideal tank
 1 ft wide by 20 ft long, 6 inches deep
 falling weight and string for power
Barge Activities
Sailboat activities
 Running (wind astern)
 Simple
 Outdated
 Reaching (wind abeam)
 Faster
 More realistic
 Ideal tank
 2 ft by 10 ft by 1 ft deep
 box fan on the end
 4 box fans along the side
Power boat activities
 Rubberband power
 Paddle wheel
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Simple
Slow
 Above water propeller
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Simple
Fast
 Below water propeller
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Fast
Realistic
Powerboat activities
 Electric
 Battery
 Solar
 Gasoline
 Model airplane engines
 “Weed Eater” engines
 Ideal tank (dependent on anticipated speed)
 8 ft wide by 24 ft long by 1 ft deep
Boat Racing
Control of model boat
 Free running
 String
 Wire
 Infrared
 Pre-programmed
 Radio control
 2 channels
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Steering
Throttle
Boat control
Model boat to real boat
 Build a model to ¾ inch = 1 foot scale
 1 penny weighs 25 pounds
 Multiply boat speed times 4 to determine performance
of actual boat
Boat Building
 Taped seam construction
 Plywood panels cut to shape
 Held together with plastic ties
 Joints taped with fiberglass
 Strip built
 Thin strips edge glued over frames
 Fiberglased inside and out
 Hybrid
 Plywood hull
 Strip deck
Small boat design class
Plywood panels are
cut to shape from fullscale patterns.
Small boat design class
Panels are taped
together end to end
with fiberglass cloth to
provide necessary
length. Waxed paper
gives smooth finish.
Small boat design class
Small boat design class
Small boat design class
References
 The Nature of Boats: Insight and Esoterica for the
Nautically Obsessed, Dave Gerr, International
Marine, Camden Maine