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Mini Tunnel (Redesigned Version) Boat Plans
Page Three
Tunnel

Before you start installing tunnel battens, place a staight edge along one of the tunnel sides to properly align the structure.

If you have not installed outer bulkheads yet, you can put the straight edge outside the tunnel as shown here. Otherwise, place yours inside the tunnel. You will be able to remove it once a few battens have been installed.

In the photo, a 96" board extends from transom to just forward of station three. A second board was subsequently added, overlapping this one, and extending the straight edge to station one.

Once the structure is aligned, it's time to square up the structure just as accurately as you can.

To test the straightness of your structure, sight down the middle to see that the centerlines on your beams are aligned.

Note that two of Tunnel Battens are installed right up against the tunnel sides; one Batten is located along the centerline of the hull; and two Battens are located 9.25 inches from the centerline (as noted on the "Construction" drawing). The last two serve to anchor the bottom edge of the coaming to the tunnel plank from Bulkhead 3 to the Transom. Forward of Bulkhead 3, the coamings curve toward the centerline and no longer have any firm attachement to the tunnel plank.

Install these five Battens first, then install the remaining ten Battens evenly spaced between them, as shown on the "Construction" drawing.

Hold the Battens in place at all points of attachement with c-clamps or spring clamps.

I attached the Battens at all points with glue only, believing screw holes will only serve to weaken the Battens.

Bilgewater will naturally flow toward the stern, so you need to provide places for it to go. Specifically, provide limbers that carry it to the sponsons where drain holes will be provided to drain the boat.

I used a router with a 1/2" corebox bit to cut 1/4" deep coves just forward of the transom beam. A fence clamped to the battens guides the router.

The router cannot get to the outmost batten. Instead, clamp a small block to the batten and, from outboard of the tunnel, drill a 1/2" hole through the tunnel side and through the batten and block.

Remove the block and you have a neat cove in the batten, and a hole through the tunnel side leading into the sponson.

The hole as seen from outboard of the tunnel. A long drill bit is called for here.

The tunnel plank can be scarfed together or joined with glue blocks as I did.

I made the block narrower than the space between batten so that they did not prevent any water from draining to the stern. Actually I could have made them a little wider, installed them tight to one batten and leaving a space only along one side.

I attached the tunnel plank (and virtually all plywood on my Laker 14, from which this picture was taken) with 9/16" brads driven in place with a manual staple gun. The brads were then set below the plywood surface with a nail set.

Alternatively, screws can be used (to be removed later) or staples (also removed).

The completed joint.

I installed a small molding to finish and seal the joint between the tunnel sides and plank. A simple epoxy fillet will also do the job.

I pre-drilled the molding, then installed with 1" nails. Most of the nails extended right through the tunnel side plywood, making it easy to tap them back out with a nail set after the glue dried.

A spray rail two inches from the bottom edge of the tunnel side completes the tunnel. The spray rails extend from the transom to Bulkhead 3.

Install these with screws driven from inside the sponson.

Besides knocking some drag-inducing spray off the boat, these rails also strengthen the tunnel sides themselves. Don't skip this step.

Alternatively, you could install more substantial spray rails, as outlined in the constuction notes for the Pro Tunnel.

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