Flotation calculator?

[brsoo]

Ok. I am looking at a old pontoon pedal boat on cl. The pontoons are 12' x 15"? I think! It's a Godfrey sr 1200 sea Ryder I think. There is no weight capacity plate. I'm guessing it's like 700-1000lbs... is there a way to KNOW how much flotation I'll have before I dive in? I want to carry 2-4 people and run in mildly choppy water...

The frame is fiberglass and weighs a lot. I was thinking about buying it and building a small platform boat with it. What do y'all think? Am I getting in over my head? Have y'all seen anyone do this? I have a 6hp 4stroke to put on it after I'm done.

 

[ahicks]

This project started taking on water (in my book), when you mentioned choppy water and the potential for 4 people on a 12' whatever, and sunk out of sight when you mentioned you have 6hp to power it.

A 16 footer with 15hp could even be scary. At least with something like that you could take it out on reasonably calm water.

 

[tpenfield]

((15"/12"*0.5)^2 * 3.14)sq.ft. * 12ft * 2 pontoons * 62lb/cubic foot = 1825 lbs (+/-)

 

[HotTommy]

The calculation above is correct provided both pontoons have a round cross section and are completely submerged. If, for example, you only want the water to come half way up, then they provide 912 pounds of flotation. That means that if the weight of everything including the pontoons, frame, equipment, engine , fuel, people, etc. was 912 pounds, the pontoons would be half submerged. If the weight of everything exceeded 1825 pounds, it would sink.

 

[brsoo]

Thanks for the response guys! I wish I went and bought it now my truck broke and I had to fix it. Now that I got it fixed I found a guy local with 55 gal barrels. I've since made a plan for 10' x 6' pontoon with 6 barrels. Which should be too much flotation and will hold whoever I put on it! Anyone know of blueprints for other plans? I am thinking about offsetting the platform a bit forward to try and balance the weight and handling...

 

[brsoo]

I'm sure no one's reading this. But just for the info. I spent $80 on wood and $40 on screws/varnish. I backed out after starting to assemble the wood. It was obviously going to weigh too much with out a trailer for it to live on. So I sold it all and bought a 14.5' v-hull aluminium boat. Some 14-15' aluminum boats still weight less than 200#s and have a capacity for 4-5 people. So I snagged one up!