: 1. Has anybody done a MC deck with luan?
I've built two MC 13's with lauan. I used some nice 3/16" (5mm?) material. I hear a lot about voids in lauan, but I've never found any. I've read that if you backlight a panel with a strong halogen lamp you will see the voids. As for the deck, I don't think it can be done with anything heavier than 1/8". The center ply on my 5mm sheets is about 3.5mm. When you are using it for planking the core doesn't resist the bending around the forms, but when you try to bend it with the grain of the outer plys and against the grain of the core for use on the deck you get a lot of resistence. If you apply enough force it will take up the curve, but you may distort the shape of your hull. Even if you don't, you run the risk of splitting the outer ply. My work-around was to rout 1/8 by 3/32" kerfs every inch along the length of the underside of the deck. This weakened the core enough to permit it to be bent to the curve of the deck. Before glueing it to the inwales I filled the kerfs with thickened epoxy. This resulted in a strong enough deck, but did add to the complexity of the job and weight of the boat. The next time I'll use 3 or 4mm marine ply.
: 2. If not, could a two-peace deck (like a Pygmy) be used?
This would work, but you've got a lot of deck/cockpit redesiging to do to make it happen. Again, I think it's worth your time to get the better ply for the deck.
: 3. If anybody has built a MC with luan can you give me any lessons you have
learned?
Yeah, sure. Lauan is cheap enough, so make up an extra of each side plank, bulkhead and half of the bottom. This way when you decide to build another one you'll have templates for all the parts you need. Another thing, don't try to build a Sweet Dream with it. Good luck.
Geo. C.