TUNNEL HULL RACE BOAT

Many different types of racing boats utilize the tunnel hull design, from small open-cockpit race boats up to those awesome F1 powerboats that can obtain speeds up to150 mph. The basic concept of the tunnel is fairly simple; air passing through the tunnel provides lift ,thus reducing drag, and the prop, which is just barely in the water provides the thrust. Somewhat like an airplane, as long as the lift, thrust and weight of the boat are all properly balanced, the tunnel hull literally flies on top of the water.

This boat was designed by Bob Dillon of Dillon Racing. Bob and other drivers raced this boat in 2006 in an APBA sanctioned race called Mini GT, a class run only in and around the Twin Cities area of Minnesota, and the Dillon Mini won almost every race. Now I haven't taken up boat racing, yet, and if I wanted to I couldn't race this boat anywhere in Texas that I know of, but I wanted to build it anyway and just have some fun with it. I intend to build it as close to spec as possible so it has all the same qualities as the racing version would have. The plans for this boat are inexpensive and can be purchased from the Dillon Racing website www.dillon-racing.com.

Below, I will track the construction of the Dillon Mini GT as it progresses along. Hopefully I can stay focused enough on this one to get it in the water before winter 2008.

Here I'm measuring out the bulkheads (left) and (right) a picture of one of the frames after it has been notched and the limbers cut out.


I used a drill press and a 7/8" forstner bit to bore out the limbers. On the right is a picture of the completed transom frame.


I attached all the bulkheads to their frames and started getting the frames up on the building jig. I spent a lot of time getting everything level and centered. It's not that it was all that hard, it just takes a while. Knowing you have it level is easier than knowing you have it centered. What I did was mark the center of my building jig and pull a string on that line, then I used a plumb bob to center each frame on that string. I tweaked it a few times over the next couple of nights. Then I checked the level and centers about 5 or 6 times again. Eventually, I came to feel it was all in place and started laying in the tunnel battens.  



The tunnel battens dropped right in place so that added to my confidence that its all properly centered.


Next I attached the sheer clamps, chines, and tunnel side structure.                                                  Then beveled all these pieces down to accept 1/4" planking.


But first I must attach the tunnel sides. Hmm, I think I need some more clamps!                                  Here both tunnel sides are on and trimmed down. Oh yeah, I did my first scarf joint!


Next up is to attach the tunnel bottom plank and the spray rails. Since this boat is 10' long, it took 2 pieces of ply scarfed together to fully cover the bottom (I scarfed the two sections in place

on the boat's bottom). I want to use as few screws as possible so except for some screws in the transom frame and at the scarf seam, the rest is glue only, thus I piled up everything on there

except for the kitchen sink (because my wife wouldn't let me have the sink).


Next the spray rails are attached and...                                                                                             ...now I'm ready to finish the sponsons.