I’m planing to use 50mm thick FinnFoam XPS insulation board for my stitch-and-glue pasific proa hulls.

The general design should be close to something like this:
http://www.derkanumann.de/wp-content/uploads/2010/04/Proa4.jpg

I’m trying to keep things as simple and cheap as possible. I don’t like working with fibers and epoxy, so I’m thinking keeping the foam uncovered or maybe I’ll just paint it. Because FinnFoam it is extruded Polystyrene, none of the cheaper resins will do. I will attach a strip of wood or something to the keel to protect it from rocks etc. If I like the boat I might add some epoxy and fiber later. I also might be able to get some heavy duty nylon(?) cloth I could use instead of glass/carbon.

First I designed a symmetrical main hull, but after doing some more research I also made asymmetrical plans. Which ones I should use? This is what the hull will look like before sanding the edges off.

Total width for the proa should be around 2 meters. Do the dimensions for the hulls and for the total width make sense? What do you think about using crab claw rig?

If the waterlevel is 20cm below the deck, I get about 200kg of buoyancy. At 10cm below the deck it’s 300kg. Me + my girlfriend = 130kg, so I think it’s enough.

I don’t have any experience with foam boats, so can’t really comment on that. I do like the general shape, should work well, and of course we always like crab claw rigs, they are simple and cheap in small sizes like this. If using a crab claw, I’d go with the asymmetrical hull, it will counter-act the weather helm of the crab claw and help the boat balance by weight shift.

Thanks for the link to that cool proa, BTW!

Hi, I strongly believe that you will not be happy with the proa made from xps foam only. Every touch with everything will rup small pieces out of your boat. trailer/roofcarrier, small stones on the beach, the dock ... everything.

You will have difficulties to attach your Akas to Vaka and Ama strongly enough and not deform the foam. Foam alone is not able to carry the rig loads.

You can build with xps foam, like the “Moth” builders do it, but you have to have a stiff outside of glass to protect the foam and to produce enough stability. Build it hollow to save wheight and money. But this is not so critical for a 16’ proa, you will need only 10kg of epoxy and just a week to cover it. And it mus not be West System ... a good industrial Epoxy will do. ( if money is the point).

In my country (germany) foam is no cheap building material ... building with plywood is cheaper ... and more durable.

If you want to avoid epoxy (for whatever reasons ever) you can be sure that a classic plywood contruction method (screw and glue)  will produce better results than foam alone.

Best Regards, Michel.

If you want to cover it on the cheap you could use cotton-cloth and some water-diluted polyurethane-paint. Its far from glass and epoxy but its better than just painted foam. There is some quite strong floor-paints based on polyurethan or Urethane, without organic solvents. They do not dissolv in water but after a couple of days the water could penetrate the paint and it would chip of eventually. Ok for daysailing or weekends where the boat would be drag up onto the beach during the night.

Johannes.

Once you have coated in the water based paint.  Try applying cheap polyester resin GRP.  It should be enough to resist the solvent, but first try a sample!!
I made a very cheap surfboard in a similar way, though the foam was coated in PVA, then covered in aluminium (cooking) foil, then glassed.  The problem was the PVA had not dried well, a pinhole allowed in some water, and out dripped PVA all over the car!!