On these larger scale launches... What is the lower deck made of in your boat? The deck I am referring to is the deck that would have the boiler and engine mounting plates bolted to.
Oak, modeling plywood..? I am wanting to use 1/4" oak- but that may be overkill. The deck would have threaded inserts to accept the bolts for the power plant.
Also is this deck removable in your boat( I would think that wise to access, but perhaps not..also did you also use a robust "joist " ( oak or birch etc) under the deck or just larger dimension basswood etc?