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Pro Tunnel Race Boat Plans
Page One
Tunnel Sides

NOTE: If you are planning to build the Dillon Composite Cockpit for your Pro Tunnel, you may want to build that first so that you know exactly how wide it turns out and can adjust your boat's bulkheads where necessary.

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The tunnel sides are just that, and they are much more. Horizontally they span the length of the hull, and vertically they extend from the deepest part of the sponsons to the underside of the deck. They are like girders to which all the bulkheads are joined. They dictate the shape of the boat, and lend it structural integrity. And, not incidentally, a portion of them become the sides of the tunnel.

Although by themselves they may seem light and insubstantial, before you are finished with your Pro Tunnel there will be stringers, carlins and cleats glued to them. They will be the backbone of your boat.

The tunnel sides are longer than a standard sheet of plywood, so you will have to join two pieces with either a scarf joint of with butt blocks (approx. 6" long will do nicely). If you use butt blocks, make certain they are on the back side of the tunnel side, the one facing the inside of the sponson.

Draw the long sweeping curve of the deck line with a batten approximately 1/2" thick. The shorter curve of the sponson may require a thinner batten. Use what works.

Also mark the stations (the locations of the bulkheads) and the Reference Line. You will also want to carry these lines over to the other side of each tunnel side, either during layout, or after cutting.

Now is also the time to consider the "fins" at the inner edges of the sponsons. The fins are an extension of the sponson sides which project above the deck. Their exact height and shape is optional; I have drawn them on the plans to about 1.5" high. You may even opt to go without fins.

They are there, presumably, to direct air along the deck, but I suspect they don't really have any beneficial (or detrimental) effect on a boat in this designed speed range.

The two tunnel sides can be temporarily joined and then cut out together. Make certain that the Reference Lines and bulkhead stations line up. The slots for the bulkheads and for the bulkhead beams (not shown) can also be cut out in this manner, vertually insuring that your tunnel sides are identical.

Carefully layout and cut out the notches for the stem and the transom beam.

The tunnel sides with notches for transom beam and stem, and slots for bulkheads. Still awaiting slots for the bulkhead beams and the lightening holes.

Lightening holes in the tunnel sides and bulkheads do in fact serve to lighten the structure a bit -- maybe 3 to 4 pounds. But these holes performs another function as well: air circulation. Air freely circulating through your hull helps it dry out after use.

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