home made pontoon

[f4imatt]

Hey guys. Great site! I am getting ready to start a build on a small pontoon for family fishing. I am thinking of using 12" concrete forms for the pontoons. Has anyone tried this? I plan on making the pontoons 12 feet long and divided into 3 sections. I will attach the 3 and use 1-2 layers of chopped mat to waterproof and strengthen the toons. I am attempting to build this for around 300-500 bucks. I would like the deck to be approx 10'x5' and plan on using treated 2x4s and osb siding as the deck. After the construction the entire boat will be coated in resin and painted. How much weight can I expect 2 12" pontoons 12 feet in length to hold? Any advice will be greatly appreciated. Thanks in advance.

[f4imatt]

I am thinking that 12 inch may be too small unless I were to do a 3 toon. By my figures from info found here a 12" tube 12' long would hold approx 546 lbs each so divided by 2 with 2 toons should hold 546 pounds - deck and toon weight. I think I may have to do square toons or larger diameter round maybe 14-16" diameter. Am I correct?

[messabout]

A 12" diameter by 12 foot long object will displace 588 pounds of fresh water. That is if the ends are blunt. A 14 inch square toon will dis place a tad more than 1000 pounds. You would surely not want to use all that capacity. Half that much might be OK. In that case the 12' round one would be good for 294 pounds more or less. That does not provide an assuring margin of safety. Go for the bigger sections by all means.

[f4imatt]

Thanks. I am thinking 16" would be much better. I will probably build wood toons in that case. I figure around 1000lb capacity will suit my needs.

[alan white]

Forget sonotubes for anything near water. They are basically plain cardboard.
As a form, they are not easy to keep exactly round, but for your needs, they would work as forms (unless you want a lot of extra weight).
As a form, spiral wax paper around a tube and glass over that, then remove the tube. You can remove it easily once you get a hold of the cardboard and pull, because the tube is actually a coil.
Yes, they make sizes up to huge, so the sonotubes are still a good idea. You can even pinch the ends for bows, but you might leave a bit of cardboard within, but so what?
I suggest you work with no longer than 8 ft sections at a time, then join with glass tape.
Sonotubes are shipped nested, meaning 16", for example, may be slightly larger or smaller than you expect. Get the largest size, the outside tube, and get both the same size.

[f4imatt]

Do you think it would be simpler to build say 2 16x16 plywood pontoons?

[alan white]

Depends on your level of experience with glassing. Plywood is a lot more work if you're proficient at both methods. It also demands more expensive materials than glass and polyester to have the same lifespan .
Probably the cheapest thing you could do is to lay mat over the cardboard tubes. You could even rotate the tubes as you lay up the glass.

[f4imatt]

Thanks for your advice Alan. I think I found a supplier that has 18" sonotubes in 12' lengths. So to start I am going to pick up 2 and divide them into 4 sections with 4 plywood inserts. I plan to roll the insides with resin for moisture resistance (condensation) and a good layer of chopped mat and a layer of gelcoat. I will post up pics of the progress.

[alan white]

Reread my earlier post. It's not going to be easy to glass inside the tubes. Just use them for forms and glass the outsides and rip the cardboard out after by filling it with water while up-ended and let the cardboard turn to mush. Otherwise, it's a waste of resin and mat. The cardboard will get wet eventually anyway, it's waxed which will reject resin, so poor adhesion too.
Leave no cardboard in the finished product. It is pointless.

[f4imatt]

I got ya now. In that case I happened on a great way to make a mold with ply and plastic sheeting. Ill see if I can find it again and post it here. Thanks

[kayaker50]

Do you think a 16 inch fiberglass tube will be rigid enough? It seems to me that it would be very floppy without some type of support inside. Just thinking out loud. Paul Hubert.

[f4imatt]

I plan on using a 2x4 top and bottom and 4-5 18" ply circles. This should give strength to the bottom and also a place to bolt the deck on. So if I get a puncture I will have the toons divided for safety. Ill try to do some sort of pic.