Pontoon boat question.

[Timmy]

I am replacing the deck on our pontoon. I have some 18 gauge aluminum sheet metal that I want to use. I know I'll have to add braces underneath to keep it from sagging (they are about 3-4 feet apart right now). I'm thinking about welding in cross pieces and riveting the sheets to the frame. Anyone see any problems with this. Also the nose cones had foam in them, but they take on water and the foam actually soaked it up. They still had about 6 inches of water in the in them after sitting for about 7 months. I am wondering if I can just weld them shut (they're are open on the top) or if the foam was not just for flotation but to strengthen the cone to keep it from deforming or collapsing. Any input will be appreciated.

[timgoz]

Tim,

I doubt if the foam adds any structural integrity to the form.

Welcome.

Tim

[ted655]

Actually the foam does add rigidity, helping prevent dings & dimples in the cones. You've learned that any foam other than polystyrene will absorb water. Since a "pint is a pound", that can add quite a bit of weight.
IF you decide to replace the soggy foam (a wire wheel on a hand grinder works well) & pour in new, you can try coating the new with epoxy to give it a waterproof skin. Then rivet a cover over to eliminate as much contact as possible. The foam will "resist" LIMITED water contact so give the water a place to go elsewhere every chance it gets.
18ga aluminium is pretty thin for a floor. Riveting is no problem. The bracing will be spaced darn close if you want to keep a smooth, fair surface. Otherwise you'll get a "burdbath" between the braces.
Even a 1/8" or (better), 1/4" underlayer will help. Are you then going to carpet over? Good footing is 1 reason to cover over ,BUT another reason to cover alumonium is glare. Out on the water, you can get a real headache & eyestrain from reflection.
Mock up a floor bracing model using 2 X 4s on a level slab. This lets you play with the spacing before you start on the boat. It lets you walk around and see how much the sheets flex.
Good luck,

[kach22i]

Originally Posted by Timmy

I am replacing the deck on our pontoon.

Was the old floor plywood?

Have you considered Coosa?

Link:
http://www.coosacomposites.com/

A lot of people have replaced plywood in their pontoons and RIB's with this product. I'm told it will hold a screw, is half the weight and twice the strength of marine plywood. The cost is about the same as you don't have to seal it with expensive sealers and finishes.

The metal you propose will require a lot of additional structure, more time, cost and weight (you might want to use it on walls or rails only). Even if you use an aluminum floor deck or lighter roof decking, cost will be high. Using corrigated or honeycomb plastics also have a certain drawbacks, but if you can get them cheap enough look into it.

[ted655]

I don't want to steal the thread here, but what I DON"T see in Coosa's specs is a claim of being waterproof. As long as the skin is not compromised it probably is. Being polyurethane, it would turn into a sponge if & when the protective skin were broken. Then what?
Another problem with these new wonder materials is availability. They are not usually available at retail stores (off the shelf). Sometimes they CAN be ordered special but you have to pay a premium price, shippimg & the like. Often you have to buy a "lift"(a full shipment, bundle or pallet).
Unless it is off the shelf, a small or 1 time project won't benefit from new products.

[Timmy]

The reason for the aluminum sheets is that I already have them (enclosed trailer that never got built) and I like the fact that I'll never have to worry about it rotting or soaking up water. And yes I am definately going to put carpet down, I think it would be hot and definitely slippery when wet.