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The
Fundamentals of Boat Design
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This
event is destined to become one of Virginia
Beach's most fun and rewarding fundraisers.
For details call David Mount at (757) 963-5795. |
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Before you develop a concept, consider these fundamentals
of boat design.
A boat floats and displaces a quantity of water equal
to the weight of the boat and the crew. If the weight
you put into a boat is greater than the weight of the
water the boat displaces, the boat sinks.
Water weighs approximately 60 pounds per cubic foot
(12" x 12" x 12" cube).
For illustration, let's look at the smallest size boat
in the Cardboard Boat Regatta, a guppy with a single
crewmember. Once you understand this example, it will
be easy to calculate for a larger boat.
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Click
image to view SKETCH #1
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The above sketch is 24" wide, 12" high and
72" long, with an additional 24" tail and
36" nose, which makes the overall length 132" or
11 feet. The inside volume of the boat is 17 cubic
feet (LxWxH - 6' x 2' x 1' - 12', plus 2' for the tail
and 3' for the nose). As we stated earlier, water is
60 pounds per cubic foot; therefore, this boat's total
displacement weight is 1,020 pounts (17' x 60 lbs).
The side of the boat is 12" high; therefore, it
takes 85 pounds to push the boat down into the water
1" (1,020 pounds divided by 12 = 85 pounds). If
a single crewmember weighs 170 pounds, the boat will
be pushed down into the water 2" (a 2" draft
or waterline). The weight of the boat was not included
in these calculations, so the actual draft would be
slightly higher. A 2" draft gives the boat approximately
10" before water enters from a wave.
That's the basis of floating (designing) a boat with
one crewmember. If you put two crewmembers in this
boat (add 175 lbs.), the draft would be 4" and
would leave only 8" to the top of the boat. This
may be okay for smooth water, but a little wave action
might sink the boat.
Following are other important aspects that influence
the final design of the boat.
Types of Hulls
Hulls with flat surfaces are easier to build but are
not as stable in the water as others.
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Click
image to view SKETCH #2
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Types of Prows
Some bow types deflect water better in wave
action than others. Keep in mind that you'll need to
blend your prow shape with your bull bottom shape or "footprint." Consider
where the waterline will be when your boat is loaded.
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Click
image to view SKETCH #3
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Boat Stability
Center of Gravity
The next area to consider is boat stability. The below
sketch shows a crow section of a hull and the center
of gravity (cg). As crewmembers position themselves
in a boat, some of their body obviously sticks out
of the boat. The lower the crew sits in the boat, the
lower the cg. Your goal is to make the cg at or below
the draft. This makes the boat more and more difficult
to tip over.
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Click
image to view SKETCH #4
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Balance
The balance of the boat forward and aft is also very
important for proper performance. When positioning
the crew, keep the most weight to the rear of the boat.
By doing this, the prow will tend to stay up in the
rough water and keep it from entering the boat from
the front.
Design Creativity
So far, we've only discussed the technical issues of
boat design. The more creative part of your boat building
project is the boat's theme and decoration (for both
boat and crew). The sky's the limit, as long as you
follow the basic construction and safety rules on this
Web site.
Your boat could look like a Viking ship, a battle
ship or a tug boat. It could be built to look like a
banana, a tube of tooth paste, or a school bus. Let your
imagination be your guide. Let's get building!
Construction Techniques
If possible, cut your boat from one big sheet of cardboard.
You can create a single sheet of cardboard by taping
several sheets of cardboard together. Taping six 6' x
8' pieces together creates one 18' x' 16' piece.
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Click image
to view SKETCH #5 |
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Click image
to view SKETCH #6 |
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Click
image to view SKETCH #7
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Click image
to view SKETCH #8 |
Click image
to view SKETCH #9 |
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