Plywood twist- were these handed panels? if not, this could be the problem.
Ply is rarely flat, or bends evenly, you need to work with the twist. I tape the panels together flat, then push the deck out to shape. Use super glue to ‘spot weld’ before applying epoxy fillets.
Some years ago I had weed problems on a calm pond and saw a photo of Cliff Daniels’ ‘Prismatic’ R6m -said to be good in calms and weed- so I built a small one. A single sheet of plywood gave a 23” - 584mm hull giving a displacement of 2497gms or 5.5 lbs (I later fitted a new rig and reduced the ballast, a mistake ! heavy is good)
This made a simple boat with a canoe stern, internal ballast, and the skeg just glued straight on to the hull, an ideal beginners model? or so I hoped.
It sailed amazingly well, until I raced on a larger pond and found it sailed in a slight curve to port, as the skeg was a tiny bit off the vertical. Then as the wind got up and it heeled even further, most of the grip went and the leeway angle opened up to ~30 deg or so. Back to the drawing board.
http://www.southwold.ws/smyc/2003/photos.php?count=10
The next version is shown on the sketch, the canoe stern is replaced by a transom to make the skeg easier to fit straight. I should fit an end plate to help the grip in strong winds. This is 300mm long and fits in to a coat pocket.
The boats sail well in light conditions (and laughs at weed), having good momentum, surprisingly little wetted surface area and low form resistance. For a heavy boat -DLR 678 - it makes very little wake and just cuts through the water. The ’plank on edge’ hull is, I suppose an simple form of the low drag ’submerged buoyancy’ style of design so popular these days with ferries etc.
They can point high in good conditions ~ split 90°tack, if sailing fast and upright (less than 45 deg heel).
In strong winds they heel a lot ~70 - 80 deg and loose grip, much leeway, they will reach well, but won’t point. I feel most side force comes from the immersed deck… Bow burying, even in gales is not a problem, with all that flare and overhang.
With no initial stability, carrying sail is a problem. Ghosting sail is ~ 460 cm sq, giving a SA.DT of 9 ! and the storm sail is about half that.
The ballast ratio is 85% and should be higher. I would make a lighter rig and try for a lighter hull, or add freeboard and more ballast. An end plate would help.
They were a lot of fun to sail but frustrating in winds. Radio could help, along with some sort of wing on hull and rudder and Brett’s rig.
These are very wet boats , about as close to a submarine as a yacht, so look after the radio .
I replaced this boat with a traditional long keel yacht still good in weed and light winds but having the stability the Prism lacked. Unfortunately it’s just too long for a Footy and needs to be reworked.
For traditionalists the Footy works out as a 1/4 rater, far more elegant in my view.
I don’t know how much of this is relevant, but I look forward to seeing Phin sail and fancy building one myself.