EZ Tunnel Race Boat Plans
Page One
Tunnel Plank
The tunnel plank is contructed from three main pieces of plywood joined by plywood butt blocks.
Butt blocks are pieces of plywood, the same thickness as the pieces being joined, glued over the joint.
The two largest pieces are first trimmed to width (see plans for demensions), then shortened to length. The long ~14" wide scrap pieces are set aside to be used as glue blocks for this structure.
Cut the notch in each piece, keeping in mind that these pieces are NOT identical, but are mirror images of each other.
The two tunnel plank pieces are laid out updide down, lined up carefully and glued together with one of the long, 14" wide glue blocks.
Note that the glue block does not extend all the way to the forward ends of the plank halves, but falls short by about six inches. The reason for this will become apparent later.
With the joined plank pieces turned right side up, join the third piece to the forward end.
A glue block about 12" wide will suffice here.
The seam between the two larger pieces becomes the centerline of your boat.
Now, locate the "stations" for the four bulkheads. Measuring from the bow, stations are located every 24 inches.
Draw a pencil line across the tunnel plank for each station, making sure they are precisely 90 degrees to the centerline.
A 2" wide beam is installed at each station.
The beam at station one is placed aft of the pencil line. The beams at stations two, three and four are placed forward of the pencil line.
Furthermore, while beams one, three and four are installed on edge, beam two is laid on it side. This is necessary because your foot-operated throttle will be installed near here and might otherwise be in the way. In fact, on my boat the throttle is installed on top of this beam.
Install the transom beam at the aft end of tunnel plank. The transom beam is 3.5" wide, but you may find it easier to make it in two pieces, as I did.
Here the transom beam is clamped and screwed into place.
Note the length of 2x4 just forward of the beam, temporarily clamped there to hold the plank flat. My plank would not lie flat on its own; do this same if necessary on your boat.
Same with the bow beam.
Now, go back to those 14" wide plywood scrap pieces.
Cut butt blocks to fit between the beams two and three, between three and four, and between four and the transom beam.
Turn the plank upside down again.
Establish the station lines on this side of the plank by carrying your pencil lines around the edge and then across the bottom.
Measuring outward from the centerline, establish the finish width at station two and at the bow.
Bend a thin (1/4" or so) batten along the full width and through the established widths at station one and the bow. Strike a line along your batten.
Cut along those lines to establish the final shape of your tunnel plank.
A short piece of butt block completes the joining of the two larger pieces of tunnel plank and ties them together with the smaller forward piece.
The remaining part of the joint, between the larger and smaller pieces, is already "butt blocked" on the top side and no further blocks will be needed. This joint is far enough forward to be clear of the worst stresses your boat will experience on the water, and it should hold together just fine.
Time to start getting rid of extra weight.
The plans specify slightly larger cut-outs than what I removed from my boat. I wasn't sure just how far I could go in this regard, but in the end I feel certain that I could have taken more, and I have drawn the plans to reflect that.
My cut-outs removed eight pound of plywood. These larger cut-outs should be closer to ten pounds (although it all depends on the plywood you use).
The completed tunnel plank (except that I had not installed the last piece of butt block at the time of this photo).
