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   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  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      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  10 lbs/hp  15 lbs/hp  20 lbs/hp  25 lbs/hp  30 lbs/hp  35 lbs/hp  40 lbs/hp 80 knots 60 knots 50 knots 42 knots 37 knots 33 knots 31 knots 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      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   Simple Slow  Above water propeller   Simple Fast  Below water propeller   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   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 full scale 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