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Pro Tunnel Race Boat Plans
Page Three
Initial Assembly

I started with a dry assembly with the boat rightside up: it is easier to slide the bulkheads into the slots in the tunnel sides from the top. Slide the beams in first to help hold the tunnel sides upright, then slide the plywood bulkheads in.

You may also choose to permanently assemble this stage with the boat rightside up, and then turn it all over.

Beams and bulkheads in place.

APBA (OPC) Rule #12A (2009) requires that the termination of the sponson be made of plywood at least 3/4" thick and be at least 16 square inches in size. "... the purpose of the bulkhead is to cap the ends of the stringers," presumably to prevent these stringers from piercing another boat, like a spear or dagger, in the event of a collision. If you are not going to race in APBA events, you may opt for a thinner bulkhead here.

The edge of the terminal bulkhead which attaches to the sponson side is cut square. The remaining sides are beveled. I cut all those sides, using a bandsaw, to a 13 degree bevel. The edges to which the deck and the sponson pad attach remained at 13 degrees. The remaining two edges needed some adjustment. I used a spokeshave. A plane, or file, or belt sander could also be used.

The stem attached to the tunnel side with a glue block.

The 2" hole forward of the stem is a vent, which is required by APBA for boats in which the driver is restrained with a 5-point harness. When a boat capsizes, it tends to become stable upside-down due to air trapped in the hull. The vents allow this air to escape, causing the stern to sink and making it easier to rescue the driver (should it be necessary).

While not required for GT Pro boats (or for non-racers), it seems a good idea anyway. A boat that has stabilized upside-down still has to be righted by the crew of the rescue boat, making their job that much harder. If the boat is floating vertically, with the bow ring conveniently poised a couple feet above the water, they can simply hook on and tow it away.

The tunnel sides and the bulkheads with their beams all assembled and upside-down, ready for the next steps.

I found it necessary to put a temporary cross member between the sponson tips to keep the spacing correct and prevent twist. I used a piece of lumber about 5" wide and exactly 42" long. This brace will be particulaly important when you start bending in the sponson longitudinals.

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