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Laker 14 Tunnel 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 straigt edge outside the tunnel, as I did. 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 it up just as accurately as you can.

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

The battens follow a very gentle curve from the transom beam to station three, then the bend increases. Most of the force of this increased bend is imposed on the beam at station two. While the force from any one batten is minor, the accumulated force of seventeen battens is enough to bend the beam.

I shored up this beam with a length of 2x4 placed along its top edge and screwed to the bulkheads. I did not remove it until after the hull was turned over.

Likewise, the bow beam is also subject to bending from the collective forces imposed by the tunnel battens. I attached this short piece of 2x4 (longer would have been better). A single screw holds it in place, passing through the beam at the centerline and then into the 2x4.

Allowance will have to be made so that this screw can be remove later, and this is discussed later on this page.

Hold the forward end of the batten in place with a small scrap of lumber or plywood screwed to the beam. Put some masking tape or plastic packing tape on the scrap so that it does not get glued to the boat.

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

Make certain your transom beam notches are the proper depth before you start gluing things together.

The final lengths of the battens aft of the transom beam is is laid out in one of the plans drawings.

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 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.

Water that finds its way aft of the transom beam will have to be drained directly out of the boat -- it can't get to the sponson from here.

I routed limbers in the battens as shown here. Only the short battens that lie between the coamings, and the ones just outside of that group need limbers.

If you are building the pleasure boat layout, then all your battens will presumably be cut short and all will need limbers. (See drawing, "Tunnel Battens.")

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) 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.

A hole in the tunnel plank allows later removal of the screw that holds the bow beam support in place.

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. My rails extend from the transom forward about 96".

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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