I'm finding out folks talk about proas like they talk about sex. Most talk about it a lot more than they do it. The ones who do it a lot don't talk about it.
Gizmo was designed at the urging of Craig O'Donnell who edits the Cheap Pages. In there is a section on proas. Like most of you I have never actually seen a real proa but I think it's good practice to do an unusual design once in a while.
Proas don't tack through the wind as would a normal sailboat. Instead they are symmetric about their middle and to reverse direction you reconfigure the rig to sail the other way and take off. What was your stern is now your bow. Is that clear?? If you look at the rig drawing shown above, Gizmo is rigged to sail from right to left. But if the sail were dipped to point the other way, she would sail just the same from left to right. In the case of the lateen sail shown here you might also just let the sail swing around the mast so it points the other way. The balance float which is called an ama is always on the windward side of the main hull. The advantage of the proa is that, under certain conditions, the boat can be very simple and fast. Essentially proas are sailing canoes. The ama provides balance to a rig much larger than can be carried by a normal canoe. With the ama "flying" a bit over the water you have a very slim main hull being pushed by a big rig with a crew sitting in comfort and safety.
But getting this all to work is a challange. Historical proas were ocean boats in the trade winds and could take their time in tacking, if they ever had to. They steered with a long oar over the current stern and reset the sail with each tack. You can't do that solo or in crowded waters. The rig shown might help having two stout rudders that swing up either way in shallows. The skipper locks one in the straight position and steers with the other and can swap back and forth. I got the idea from Phil Bolger. I don't know if it has ever been tried for real. Phil intended it to steer with the bow end rudder but I think it might steer with either end. The loads on the aft rudder might be quite high so the rudders are "balanced" quite a bit in that the pivot axis is almost on the rudder's centerline and not on its leading edge. These boats are always big experiments and don't expect to get by without a lot of tinkering. I think a proa is a very simple idea that is hard to deliver properly if it must be single handed in crowded waters.
Gizmo is probably sufficient for two adults and no more. Remember it is just a long narrow canoe. I kept the total width at 8' for easy trailering but you could widen it easily. The mast shown is unstayed but is set up so that you can run stays form the masthead to the ama for really hard sailing. The 94 square foot sail looks small for a 20' boat, but big considering the 2' beam of the main hull. Commodore Monroe had something like this in Florida a hundred years ago only 30' long and heavy. It planed although he didn't use that word because it hadn't been invented yet. I'm wondering if it was the first planing boat?
Seven sheets of 1/4" plywood build Gizmo with taped seams. No jigs or lofting.