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Mini Tunnel (Redesigned Version) Boat Plans
Page One
Tunnel Sides & Bulkheads

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 outboard face of the plywood -- that is, the surface that faces the interior of the sponson. The butt block can be glued 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 reference line and station lines onto the tunnel side blank (see "Tunnel Sides 1" drawing). After cutting out the tunnel sides, carry the reference and station lines onto the opposite face.

Find the edges of the tunnel side by measuring above and below the reference line at each station ("Tunnel Sides 2"). Bend a batten through these points and draw the lines. Note that the bottom edge is a straight line from Bulkhead #3 to the transom.

More about drawing curves HERE.

Once the first tunnel side is cut out, it can be used as a template to cut the second one. But don't neglect to draw the Reference and Station lines on this one, too.

Locate the cutouts for the beams at each station. Beams at Stations 2 through 5 are 3/4" x 2". The transom and bow beam sizes are shown on the Transom and Bulkhead #1 drawings repectively.

Beam cutouts can be cut slightly oversize to make installing the beams easier.

Layout and cut the lightening holes as suggested in the plans, or as you see fit. Not much weight will be saved here, but these openings allow the free flow of air through your hull to help keep it dry.

Bulkheads 2-5 have two pieces each side of the hull -- one outboard of the tunnel side, and one inboard. Bulkhead 1 and the Transom have outboard sections only.

All points on the bulkheads are measured horizontally from the centerline, and vertically above or below the reference line.

For each bulkhead, start by drawing two lines exactly at right angles to each other. The horizontal line is the reference line; the vertical is the centerline. Locate the several corners of each bulkhead section, and draw the edges.

Layout and draw the notches for the stringers.

Also, draw a line that shows where the bottom edge of the beam crosses the outer bulkhead section (the inner section's bottom edge is exactly aligned with the lower edge of the beam).

SUGGESTION: After laying out a section of bulkhead, cut it out very roughly, staying, say, an inch outside the lines. Then screw it to a second piece of similar size and cut then out together.

After cutting out, carry the reference line around the edge and to the other side.

Cut lightening holes in the bulkheads as space allows -- generally, below the beams on the outer bulkheads and above the beam on the inner bulkheads. Again, weight savings will be minimal, but they will facilitate air circulation through the hull.

Glue cleats (approximately 3/4" x 3/4") to the edge of each bulkhead section where it will be attached to the tunnel side.

Make certain the cleats are on opposite side of the bulkhead from the beam. EXCEPT at the transom, where the cleat and beam must be on the same side. Therefore a shortened cleat must be used on the transom so that it does not block the beam notch in the tunnel side.

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