: . . . The Folboat's pontoon has an inner bladder and an outer shell and is very
: rugged according to one guy. I couldn't find out the volume and size but
: it looks to be OK. The price is right.

Are you planning to carry a pump to inflate these things when you need them. Seems they'd be a bit large to inflate by lung power.

Have you considered making your own collapsible pontoons from plywood and fabric? What I'm thinking of is something along the lines of the Boy Scout "kayaks" which have been fairly popular. These designs are cut out of plywood pieces which are attached with strips of heavy canvas and contact cement. When bulkheads are installed the plywood flexes around them to give a wide, but usable hull shape which is nice and stable for inexperienced Scouts. With the bulkheads removed these boats fold up flat for transportation and storage, with the canvas serving as hinges.

I think you could do something similar to make your own pontoons cheaply and fairly quickly. Use thin plywood (1/8th inch or 3mm marine plywood) and cut out profiles of the pontoon shape you want. A crescent shape seems to be something that might work. to get them to flex properly you might need to slit them in half. Use contact cement or gorilla glue to hold these shapes together, and use some wider canvas to form the top. Leave the center open so you can reach inside to shove in the bulkheads (cut from 1/2" or 3/4" plywood).

You could go with either 1 or 2 bulkheads. With the bulkhead(s) removed these things would fold along the center seam line.so a pontoon 15 inches tall would fold to 7 inches wide. If made with thin plywood this would be about 1/2 inch thick. That should be small enough to go inside a hatch, or bungee to the deck.

You can make a flap to cover the top opening and keep out spray. The thicker plywood of the bulkhead gives you something substantial to mount to your crossbar, too.

A couple coats of paint on the canvas does th watrproofing bit as well as it would do on a SOF kayak. Instead of cotton canvas and contact cement I suppose you could use Dacron and attach it ot the wood with fusible fabric adhesive, Like the Platt monfort Geodesic Airolites. Then you could waterproof them with tough urethane or polyurethane. Whichever way you go, your pontoons will be collapsible; foldable so they can go under the deck, or stay on the deck; and you won't need to huff and puff to inflate them.

If you have some cheap lauan plywood around you could knock out a prototype in a couple hours. That is thicker than you might want, but it should be flexible enough to give you an idea of how it would work.

Just a thought.

PGJ