Not bike related, but boat stuff.

[wymple]

I've been thinking for years about a home built pontoon boat. I can't just go buy pontoons, being a pensioner sees to that, and I want to build them anyway. I've researched, and there are widely varying opinions about using closed cell foam filling, or an air filled setup. With air, it is common to use 3 cells on each side, as rupturing one is no big deal. Foam adds to the weight, but no worries at all about ruptures. However it will waterlog if given the opportunity, and can suck up a couple hundred lbs of water. I've gotten this novel idea that I can build the pontoons as a single cell, and fill each one up with long pieces of 3 or 4 inch capped pvc pipes. Very little chance of rupturing very many of those, and flotation enough for the worst of circumstances. I haven't done the buoyancy math, but it seems like a good way to easily seal air, and avoid the foam hassle, which I hear is expensive as well. Any thoughts? You guys are always on top of any unseen problems.

[chuck hahn]

Got any buddies that do the spray foam insulation for filler????? kinda as a favor..LOL

[Steve]

Consider the weight of all those PVC tubes vs the foam. I would think that having that many tubes would be rather heavy.

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[Brendan W]

More like creating unlikely problems
My 2c. Presuming you build the pontoons with ply. Make air your primary bouyancy. Strap in some blocks of foam as back up bouyancy should a cell ever be punctured.Typically about 20% of the tank volume. Seal each of the three compartments well and put in an 8" inspection hatch in each. The proper round ones are only a few bucks. Not only can you see what's going on but in fine weather you can ventilate the tanks and it's easier to have access to the inside for repairing inevitable tips and bumps.Most holes are made along the sides of the 'tanks' so consider a second skin on the inside of outboard sides of the pontoons.
I would not rely on foam filled compartments nor sealed up hidden pvc pipes that could neither be inspected or replaced.

[Crankthat]

Possible to make a air bladder out of innertubes?
Cut one open and reseal to holding pond rubber using glue made to join roofing rubber or what they use for holding ponds?

[chuck hahn]

Or buy a ton of tire patching kits to get the actual glue...LOL

[wymple]

I didn't think the thinner pvc pipes would make a lot of weight, and inspection access should be easy enough. What could be easier than capping a pvc pipe on both ends? I suppose I could just partially fill pontoons with some expanding foam or foam blocks to get safety flotation. I fully expect to do a really sturdy job for strength and safety as I have a habit of overdoing things anyway, the result of not being engineer enough to determine safe limits.

[Steve]

I didn't think the thinner pvc pipes would make a lot of weight, ...

Once you do your calculations to figure out how much air you will need to float your weight, calculate the volume of air that will be trapped when you cap your PVC pipes, so you can determine how many pipes it will require. Now, go down to your local "big box" store, grab that many pieces of pipe and hold them. You will be surprised how heavy it is.

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[Jethro]

Yep, I'm with Steve, I think it's going to be ungodly heavy. Give me an idea of your desired, finished product. I boat a lot and have seen everything, but some more information is needed for guidance. What size are you looking to make? How many passengers? Fishing, cruising or both? What's your power going to be? Will it need to be trailered to it's spot or will it live on a single body of water? Give me as much information as possible. There are a lot of forums I am on for boats with amazing nautical engineers that might be able to guide you.

[wymple]

" What size are you looking to make? How many passengers? Fishing, cruising or both? What's your power going to be?"

Haven't settled on anything yet, but the main body of water it might see is the Mississippi, and I don't care for small boats on big water, except for the canoe. I doubt I'd go under 16 feet, and probably 18-20, width around 7-1/2. Won't be no big loads either, maybe 6-800 lbs. That's a pretty easy target to hit with lots of reserve. I have no idea what the propulsion will be, not less than 40-50 HP. Hell, I might engineer up a real motor. I have read that most high end builders do not use foam, and opt for air cells only. I kinda like the idea of a tritoon also. Those are sleeker looking using smaller diameter pontoons. I'd like to start on something this winter or early spring, getting in the water next season. Friend of mine is president of a boat club, so I may join. It's really nice middle class place, no snobbery.

[bonanzadave]

get 10000 of those noodles....

Gladon NT240 Galdon product number NT240 is also known as the Water Log noodle pool toy variety pack. It comes with a quantity of 20 noodles per pack. These noodles come in assorted colors such as red, blue, yellow, and orange. The pack also includes varying exterior finishes on the noodles ranging from round to scalloped shapes. The Gladon NT240 swim noodles measure 58 inches long by 2.5 inches in diameter, with a hollow middle. The durable, closed-cell foam helps to provide extra buoyancy. Each individual noodle supports floating a weight of up to 200 lbs.

[earlfor]

Common hardware store expanding foam is open cell and will soak up water like a sponge. It is not suitable for marine flotation use. Two part, marine expanding foam is closed cell and does not absorb water to any extent.

[wymple]

I've read that it will break down and absorb water if it's exposed to wetness long enough, whatever that means. The knock on it is that it sticks to almost anything, and if installed by expansion it rules out welding on metal pontoons for repair. I hear..?..it's kinda pricey. Wonder how long those noodles would hold up, .

I found this info, pretty good

https://www.glen-l.com/weblettr/webletters-7/wl55-flotation.html

[robertbarr]

The larger PVC is heavy enough to be a problem to transport, even. You'll see crews using at least a backhoe to install the stuff as culverts, for example. 2-foot outer diameter PVC is typically almost 60 pounds per foot of length, empty. Wall thickness of over an inch, closer to 1 1/4", so you net 21.5" of ID for your air, so maybe 2.5 cubic feet of air per foot.

Also consider that each 10' tube would add at least 600 pounds to your towing weight. You have end caps and fastening hardware to add to that.

1 cubic foot of water equates to 7.4805 gallons of water and weighs approximately 62.4277 pounds, and that's if your 'foot of PVC' is completely submerged, so you'd net about 120 pounds of buoyancy per foot; obviously that's ludicrous, since you won't have those pipes completely underwater. Your 'weight to benefit' ratio is really pretty sad.

[earlfor]

I've read that it will break down and absorb water if it's exposed to wetness long enough, whatever that means. The knock on it is that it sticks to almost anything, and if installed by expansion it rules out welding on metal pontoons for repair. I hear..?..it's kinda pricey. Wonder how long those noodles would hold up, .

I found this info, pretty good

https://www.glen-l.com/weblettr/webl...flotation.html

Instead of pouring foam directly into the hulls, Use cardboard boxes to make foam bricks that you can place/attach in the hulls. Line the box with a plastic trash bag and pour the foam into the bag. Once set, remove the foam "brick from the box and tie the top of the bag shut. Put it where you need it. They then can be removed to weld/repair, etc. Keep in mind, it will be necessary to place foam volume in proportion to weight distribution in the hull. That results in more flotation volume where the engine/batteries, and any other concentrated weights are located. The hulls should sit level when flooded. Also, rule of thumb is 50% more flotation capacity than actual weight of components. Include passenger weights in overall weight estimation.

I would install stringers in the hulls to mount the foam blocks on so they don't sit directly on the hull. I would be a good idea to install bilge pumps in the pontoons.

If you're going to scratch build pontoons, a rectangular cross section is much easier to build than the commercial aluminum cylinder design. A mild V bottom with a touch of rocker will be more seaworthy and better handling than a tube. It will also be more efficient and require less power.