4 inch pvc pipe raft.

hey,
ive entered a raft race , and was going to build a raft using pvc pipe, 4 inch in diameter. a simple catamaran design. i weigh a hefty 252lbs.
could any 1 tell me what length of pipe wud i need on each side to float well ?
i am guessing maybe two 11 feet lengths on either side, but and info would be greatly appreciated,
regards

 

I don't think 4" pipe will do it. Also, PVC pipe is very heavy and I suggest you use stryene pipe. If my math is right Pi=3.14 x 1/2 the diameter(2) x 11' (132")
comes out at 829 cubic inches. 1728 cubic inches in a cubic foot which floats 62 pounds in fresh water.What you have is each pipe will float about 32 pounds less it's weight. A 10" pipe. same length will float 1.20 of a cubic foot or 74.4 pounds.
that means the top of the pipe is just showing at the surface--it is not floating on the surface like a rubber tube.
10" or larger is quite expensive. Find a way to lash inner tubes together with a piece or two of 1/4" plywood on the top.

 

so if that is correct even with 4 ,11 foot , 4 inch pipes the raft wouldnt even float would it? sorry for being slow with the math.very new to this stuff

 

That is right Tubes are a much better way to achieve flotation. That is why inflatables are popular. How much do you want to spend?? Any specific requirements?? Give me this info and maybe I can offer some specific suggestions.

 

ok thanks , my reasoning for going with the pipes, instead of tubes or barrells was to gain speed, looks like its back to the drawing board.

 

Put a piece of ply on the top and a piece of ply on the bottom each with holes drilled on all 4 sides then get some cheap nylon rope and lash the 2 plys together with 4 used inner tubes in between. Now you have a 4' x 8' raft. don't forget some sort of rope railing so you can stand up with a pole to guide off rocks

 

PVC pipe is not a great material for a boat but in this case the 10", 11' long pipe should do the trick. The 10" pipe is just under 6 cu ft volume or 372 lb minus the pipe weight. Two such pipes is over 700 lbs flotation, unless my math got screwed up. That should allow enough for some structure, your weight and float at about half depth or so.

One guarantee is that a tube raft is slow. Maybe you could borrow some large PVC pipe. Driveway culvert will also work although it has corrugations that will slow it down some but not as much as tubes.

 

thanks very much for the help.

 

Your math is not correct, the volume is Pi X 4 X 132, 1658 cu ins or 0.96 cu. ft., so it might be possible to get enough bouyancy.

Each tube will support exactly 60 lbs assuming 4" outside diameter, but in reality it will be 4-1/2" which will add another 7-1/2 lbs , so for Rick's weight and the weight of the tubes etc, he needs at least five tubes just to float, six to keep it all balanced. That's 12 ends to cap off (I assume glued caps), so he may be cheaper and a lot drier with two 8" pipes.

 

finished and tested

i got 2 9inch pvc pipes 11 feet long . sealed them front and back, attached traffic cones to the front and also sealed them. the pipes are spaced about 2 feet apart , the raft if very bouyant,stable and easy to row, thanks for all the help.

1 last question would it be worth my while to attach oarlocks and have 2 oars like a row boat or just stick to a kayak type oar, i really wana win this race haha.

 

picture so far

http://www.dropshots.com/rickjames2#date/2009-06-15/12:49:44

 

Hide some electric motors in the pipes

I would go with oar locks, thats only because I have never paddled any other way.

 

Looks like a flying machine to me. You need to check the rules, if they exist, in case proper oars are not allowed.

 

That is a quick build - well done.

Oars and rowlocks will be best if permitted. Will be a little more difficult to see where you are heading.

There will also be a slight advantage to have cones on the stern so the water exits clean rather than dragging behind the bluff stern.

Rick W

 

victory

i won the race , it was 2 miles long took approx 40 minutes ,delighted thanks again.