JEM Watercraft

Hello everyone. I am new here to the forum so please excuse me if my questions are a little silly. I have just seen the free plans to build a pontoon. They look really awesome and straightforward and thanks to they guy who put it up. What I would like to know is would it work if I made the pontoon exactly half it's size. I would like too make it a bit smaller so that it's easier to carry to and from the water. It will be used mainly for fly fishing and will only hold me. Actually...what is the smallest i could make this particular pontoon to support my weight of 80kg's. My plan is to take the current measurements on the plan and half them all exactly...would this work...or am I headed for trouble?

Any response would be greatly appreciated.

Thanks

Jason

You'd be headed for trouble. Scaling all dimensions 1/2 would have water floating right up the deck line.

Thanks for the reply jem. That sucks. I thought that since it will only be holding me up it would be ok. Just goes to show what i know Would it work if i cut down the length of the pontoons, but kept the width standard and filled the voids with styrofoam? If that will not work thanks for the advice. Saves me some cash

If he scaled ALL dimensions to 1/2, (original dimension of 2' would then be only 1') he would end up with a pontoon only 1/4 the size of the original. Scale down by the square root of 2 or 1.414. If a dimension was 2', make it 1.4 feet. Scale all others accordingly.

But, you may be better off building a canoe from which to fish?

Kayak Jack wrote:If he scaled ALL dimensions to 1/2, (original dimension of 2' would then be only 1') he would end up with a pontoon only 1/4 the size of the original.

But, you may be better off building a canoe from which to fish?

Jack and Matt correct me if I am wrong, but wouldn't scaling all dimensions (length, width and height) by 1/2 give a volume of 1/8 of the original?

Jason, It seems to me that if you built it smaller and filled the voids with Styrofoam, it would probably end up heavier that a hollow full sized one. With hollow pontoons, you could put in a hatch for storage inside of them.
Also filling the voids with Styrofoam would guarantee that if any water ever got in there it would not dry out. You might be better off just carving pontoons out of Styrofoam and fiberglassing them.
I would go with Jack's suggestion of building a canoe or pirogue. In fact, I have built a pirogue and am working on the canoe. A pirogue would be lighter and easier to build, carry and paddle.

Jimmy

I missed your second question. If you built on pontoon to full size, cut it in half laterally, install a transom on both, and used the 2 halves for both sides, you could hold up to 136k (300 lbs) on board.

Jimmy's right on his proportion and I was wrong. Thanks for catching that, Jimmy. (You get an "Atta boy!") To get a solid that is 1/2 the volume of the "original" build it 0.794 in length, width, and height.

If a pontoon were to originally be 8' X 2' X 1', it would then be:

(8' X 0.794) = 6.352', or 6' 4 1/4" long
(2' X 0.794) = 1.588' or 1' 7" wide, and
(1' X 0.794) = 1.794' or 1' 9.5" high

That may be more than you wanted to know about it.

Jack, you might want to check that: "(1' X 0.794) = 1.794' or 1' 9.5" high". Me thinks that you poked the "+" instead of the "x".

Jimmy

I'm gonna go back to 'ritmatik again. Lesse, if a train leaves New York City heading east at 50 mph, and another train leaves San Francisco heading west at 75 mph, which one goes under first?

Thanks, Jimmy.

Jack

Thanks for getting back to me guys. You boys really know your stuff. Some of it is a bit over my head i am afraid. The idea of carving out of styrofoam and then covering the while thing with fibreglass was actually on my mind. I just had know way of knowing whether or not the thing would float. The inflatable pontoon boat that I wanted to buy has pontoons of about 8 foot long. Not sure of the other dimensions though. Maybe I can elaborate a bit on the idea I had.
What I thought might work was to take the original pontoon size of 3.8 meters and make it about 1.9 meters long. The width I was going to bring down to about 300 mm and I was going to keep the original height of 42.2mm. Actually...writing it out like this has just made me realize that it is not really half the size, since I am keeping the height the same. Jem... would this not maybe sort out the problem of water coming right up to the deck? In the end the Pontoon would be 1.9meters long x 300mm wide x 422mm high. Please excuse the mm measurement but thats what I am used to down here in South Africa.

Thanks in advance guys

Jason

I might very well be wrong, but it seems that if you half the length and width and leave the height alone, you would be back to Jack's 1/4 volume. If half pontoons will hold up 136k, then 1/4 size pontoons would probably hold about 68k. If you fill them with foam, you will have to subtract the weight of the foam from that.