MRusson wrote:
I was going to use a non pressure treated
plywood, most likely a marine grade ply on the deck and an exterior
grade on the actual pontoons prior to fiberglass. I am a bit gun shy
of the pressure treated wood since i believe they still use arsenic as
a chemical in that stuff. Any other suggestions for the actual
pontoons?

MRusson
I would divide the pontoons into watertight sections for emergency
flotation and skip the foam which would only add redundacy, price,
weight and a good starting point for rot. I would also make each
watertight section inspectable with a hatch or seal big enough to make
the inside accesable for repairs, etc. The hatches wouldn't have to be
store bought but could be made of plywood that was secured in place
with screws and sealed with a non-permanent caulking, say silicone or
White Lightning house caulk as opposed to 5200, as you wouldn't have to
open them but once a year, more or less. The bottom corners (chines?)
of the pontoons will have to be slightly rounded for the fiberglass to
wrap around without creating air pockets and they should also be
reinforced with extra layers of glass or something like angle iron
imbedded in caulking as they will recieve more wear than elsewhere. Try
to avoid, by proper design, water sitting on top of the pontoons for
long periods of time. The weak point of pontoons and catamarans is the
system/deck that connects them and the tendency for them to twist in
waves and wrack/wreck the boat. Some people replace rotted decks, and
you might consider building a new deck, with pressure treated plywood
topped with rubber roll roofing for flat roofs that comes in wide
enough sizes for one piece to cover the whole deck. It is glued down
with contact cement or some similer adhesive and then indoor outdoor
carpeting is glued to the rubber for a leakproof deck. Sam