Tunnel Plank

The tunnel plank extends beyond the transom 3 inches, measured from the overlay of marine plywood applied in the last step.

If you have purchased 4x12 sheets of plywood for your boat, cut a sheet to the proper width, then cut it off to its finished demensions and shape at the transom and leave a bit of extra at the stem.

If you have eight-foot plywood then a joint will be required. The best is a scarf joint, which can be made in various ways: hand planes, router, circular saw.... You could also simply butt the pieces together with butt blocks on the inside surface and a strip of fiberglass tape on the outside.

You can join your plywood off the boat and install the plank in one piece. Or you can join them in place, joining and installing both pieces in one operation, or in two separate steps.

With the exception of the coaming and deck, I joined all my plywood in place.

Spray Rails

The spray rails (here and elsewhere) serve to get spray off of the hull where it causes drag. Spray rails in the tunnel also serve to strengthen the tunnel side and the joint between side and plank.

You can choose to continue the spray rails all the way to the stem if you wish, or terminate them a foot or two short as shown.