Warren - Steve's advice is sound. I've used marine plywood, including Okume, Douglas fir, and teak buiilding small craft. All are very expensive, especially teak ply. Okume is softer and stains nicely, but Doug fir is stronger but checks. The interior laminations of teak faced ply tend to be very solt. You can get cabinet grade Canadian birch ply in half inch thickness. That has nine laminations with very smooth outside surfaces.
If half inch is not enough structure for your dinghy's span, glue two pieces together. The laminations are glued with water proof glues. Also through trial and error, I have learned to create a teak stained finish on birch plywood. Start with dark walnut penetrating stain brushed or ragged on. Quickly, with clean, dry rags, rub the finish so it is even. Then follow with red oak penetrating stain and rub the finish in the same manner as before. The red oak blends in nicely and it looks like teak. You can experiment with small pieces of ply to arrive at the color you want. Make sure the surfaces are dry before putting any kind of sealer and/or exterior finish. The nice aspect of cabinet grade birch faced ply is that you need not sand the outer surfaces before you apply the final finish.
John
