Mr. Watt et al :
I have the boat conceptual diagram posted on
http://kturnerga.tripod.com/boat.jpg

The main idea is to make the unit portable in a passenger vehicle.
Should this be a pipe dream I may have to wait until I buy the Ford
Explorer
Ken

(William R. Watt) wrote in message ...
KA Turner ) writes:

As far as dimensions of the user platform I seek to have it 4x6 or I
can go 6x8 inches. Per the weight of water being 62.4 lbs how do I
figure buoyancy needed and use of materials?

for anything to float it has to displace a volume of the medium (water)
equal to its own weight. so if your boat and everything on it including
yourself weighs 250 lb it has to displace 250/62.4 or 4 cu ft of water.
therefore the volume of the pontoons below the surface has to be 4 cut ft
or 2 cu ft each. if the pontoon is circular in cross section the volume is
the cross sectional area immersed times the length of the pontoon. the
area of a chord of a circle is 0.5 x r x r x (angle - sine(angle)) where
"r" is the radius of the circle (pontoon) and "angle" is the angle at the
centre of the circle which subtends the arc, measured in radians. however
you really want each pontoon to support your weight alone so you can, say,
sit on the edge of the boat without it that side sinking. if you've ever
made log rafts as a boy you'll recall that when you walk to one side how
it goes down and the other side comes up as you slide off into the water.


you can also calculate how much pontoon surface is in contact with the
water for frictional drag by calculating the length of the arc submerged
as the radius times the angle in radians and multiply that by the length
of the pontoon. however if you are going to put the pontoons inside the
car they will be too short for the boat to go very fast. as the boat
approaches a speed of 1.34 times the square root of the length of the
pontoon (waterline length) the amount of power required to made it go any
faster rises exponentially with the speed. if you could carry the pontoons
on the roof of the car and make them 12 ft or longer the craft would
be more practical for a motor to push at a decent speed

as for the weight of materials you can weigh them yourself (as sheet of
1/4 inch plywood weighs anything from 17 to 23 lb in the kinds of wood
most boatbuilders use), or look the weights up in a boatbuiling book such
as the popular "Elements of Yacht Design" by Skene which is avaiable in
some public libraries. (Skene does not give weights of plywood)

for a pontoon boat everything except the pontoons will be above the
waterline so you don't have to worry about costly "marine" grade. just
make sure its "exterior" grade.