Laker SC12 Tunnel Race Boat Plans
Page One
Tunnel Sides
NOTE: If you are planning to build the Dillon Composite Cockpit for your Laker SC12, 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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Construction begins with the tunnel sides.
Since the tunnel sides are longer than a single sheet of (typical) plywood, a panel must be constructed.
The joint can be scarfed. Or, as I prefer, you may use a butt block. The butt block must be on the plywood face that will end up in the interior of the sponson. Here the butt block is held in place with weights. Alternatively, you can use screws.
You will want to make sure that your butt blocks do not end up on a station line (see below) where they would interfere with bulkhead installation.
Draw your Reference Line the length of your panel, then carefully continue the Line over to the other side of the panel.
Locate the station lines from the drawing Tunnel Sides 1, then draw the lines across the panel, and continue these over to the other side of the panel as well.
At each station locate the indicated points (see Tunnel Sides 2-4) above and below the Reference Line. Note that the bottom edge of the tunnel sides are a straight line from Bulkhead #4 to the Transom.
Draw the curved lines using a batten approximately 3/4" wide and 1/4"-3/8" thick. The batten should ideally be longer than the line you are drawing, but a shorter one can be used as well. More information on this subject is included in the Construction Notes for the EZ Tunnel.
The drawings Tunnel Sides 2, 3 and 4 also show the locations where the bulkhead beams pass through the tunnel sides. Beam sizes are noted on each Bulkhead's drawing. Note that some beams lie forward of the station lines, while others lie aft. These beam cutouts can be cut a bit oversize to make installing the beams simpler.
Tunnel Sides 1 shows a suggestion for cutting openings for ventalation and weight reduction. The non-racer need only make some opening to ensure good are circulation though the hull. Racers may want to cut as radically as they dare for real weight savings.
NOTE: Small differences in weight will not really effect the top speed you can achieve with your boat, but will impact holeshot and acceleration -- attributes usually more important to racers than non-racers.
Even if weight is of little concern, I highly recommend some cutouts in the tunnel sides, bulkheads and coaming to provide ventalation for the inaccessable parts of your boat.
After laying out the Ref Line and Sta Lines on the second Tunnel Side panel, lay the first one on top, carefully align the Sta and Ref lines and then trace the outline and the cutouts.
After cutting out, screw the two tunnel sides together and trim the edges so that they are exactly the same, paying particular attention to the straight line from Bulkhead #4 to the Transom.
The tunnel sides, all cut out.
I cut a vent hole in the forward end of each tunnel side.
In the event of a capsize, vents will allow air trapped in the hull to escape and the the stern to sink, which simplifies boat recovery (and possibly driver rescue). Vent holes have been required by APBA, not sure if they still are.
I find they also make good handholds when pulling my boat that last few inches onto the trailer.
Glue a 4"-diameter reinforcement to the inside surface of the tunnel side. Then cut a two inch vent hole with a hole saw.
