Motorboard

The motorboard is about 1 inch taller than the coaming. The bottom edge is beveled (approx. 10 degrees) to mate cleanly with tunnel plank. Cleats made from 3/4" oak or other hardwood are attached to the coaming extension behind the motorboard. Glue and screw everything carefully and fully here; think about all the stress and strain it has to withstand.

Fit a filler piece between the motorboard and the transom beam. Exact thickness and wood species are not important -- I used a piece of Douglas-fir which can be seen below sticking up above the beam.

Bracing

Motorboard bracing is made from 3/4" oak or other hardwood. The transverse piece is 2.5 inches wide; the longitudinal pieces are 4 inches wide at the motorboard, 1.5 inches at the forward end.

I also added another transverse brace, about 1.5" wide, across the forward ends of the longitudinal members. While it does further strengthen the bracing system, it is mainly there to support the back of my seat. I installed it with screws only.