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Laker SC12 Tunnel Race Boat Plans
Page Six
Coaming/Cockpit

I put a cockpit, made for an earlier project, into my Dillon Sport C. Unless you too have, or are making, a cockpit, you will likely be making a plywood cockpit based on two coamings which extend from bow to motorboard.

The pictures in this section were borrowed from construction of the original Dillon Pro Tunnel.

The height of the coaming as shown on the plans is merely a suggestion. The drawing shows a tall coaming, which I find desirable for racing. Non-racers may opt for something different.

Sport C racers will be required to reinforce the cockpit. The OPC rules do not specify what that entails, so I recommend you do what seems best to you, keeping in mind that you're designing protection for yourself (or perhaps one of your children).

A suggestion: to the inside surface of the plywood coamings, and to the bulkhead behind the seat, add a layer of Kevlar, a layer of 1/2" or 5/8" foam, and then a second layer of Kevlar. The Kevlar to be saturated with epoxy.

I STRONGLY SUGGEST: After you have completed the coamings (and other parts described on this page, and the next), and they are ready for istallation, WAIT! It will be much easier to fit the deck panels if the coamings are not in the way. In fact, you will probably want to permanently install the deck before installing the coamings.

The most involved aspect of making the coaming is determining the shape of the lower edge.

I used narrow (10"-12") pieces of plywood to make a template. Rest the plywood edgewise on top of the beams and mark the beam locations. Cut notches for the beam, test fit and do whatever addtional marking and cutting are needed.

This is best done with 3 or 4 pieces which, once fitted and propped into place, can be joined with screws and butt blocks. Make the joints strong enough so that entire structure can be lifted out of the boat and retain perfect shape.

After making a template for one of the coamings, test fit it on the other side of the boat. If it doesn't quite fit, you'll need a second template.

Make the rough panels for the coaming the same way as the tunnel sides, joining the pieces with butt blocks or a scarf joint.

Use the template(s) you just made to trace the bottom edge onto the panels. The exact shape of the top edge of the Coaming may depend on the motor you intend to put on your boat. I designed the Laker SC12 specifically for the 40 hp Nissan/Tohatsu motor used for Sport C racing. This motor weighs a scanty 130 lbs., and speeds expected will be in the mid- to upper 50s (mph).

Most any other motor in the 40 hp to 60 hp range will weight considerably more -- probably from 150 lbs. to 180 lbs.

For a Sport C setup, I recommend placing a bulkhead between the coamings at Sta. 5, and the driver's seat immediately forward of that.

For heavier, more powerful motors, be prepared to place the drivers seat at least 12" further forward, to account for the heavier motor and the increased bow lift that will result from greater speed.

I test fitted the coamings before making the final cut of the slope from the high point to the bow.

The exact size and shape of the dashboard is optional. I make mine nine inches tall with a two-inch crown. 3/8" to 1/2" thick plywood works well.

I use 3mm marine plywood for the cowling deck. If you are using heavier plywood, you may want to reduce the crown, or use no crown at all.

About 18" to 24" forward of the dash, a second bulkhead to support the cowling plywood and to anchor the forward end of the steering shaft. Place it far enough forward so that it does not interfere with operation of a foot throttle.

The curved top edge of the bulkhead is traced directly from the dashboard.

The bottom of the cowling tip.

Forming the actual tip of the cowling and the sponsons will be covered later.

The small bulkhead at the bow beam rests on the cowling tip bottom piece. The curve of this bulkhead is also traced from the dashboard.

Looks like I used an additonal cowling bulkhead when building the original Pro Tunnel. I suspect I could have gotten away without it.

The forward part of the cowling deck lies upside-down on the deck. Instead of installing a ridge beam on the boat, I simply glued one to the plywood.

This piece is to be permanently installed on the boat.

On the Pro Tunnel shown here, the remaining cowling plywood was installed with screws only so it can be removed to work on the throttle, steering and other systems.

Install the bulkhead with 3/4" x 3/4" cleats along the coamings. Add an inch-wide stiffener to the bottom edge, which rests on the tunnel battens.

Instead of using screws to secure the removable deck, "hood hold-downs" (also called "draw latches") can be used, two on each side of the cowling.

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