RebelCat 5 Update October 27, 2009

Two New Centerboards

I'll get right to it. The original centerboard (CB) was made from plywood and began coming apart when water got inside - that's the nature of plywood, unless you get the expensive marine grade.

I made two new CBs, one from Oak, the other from an ordinary 2 x 8, both with aluminum sheet added. First the 2 x 8...

This is actually a old board, and I chose it because it had dried out completely, and it was straight. I'm using the best part, not the ends which have small splits.

Using a jigsaw, I cut the rough shape of the CB.

Using an electric planer, I begin to create the foil shape, but only on one side. The other side will be covered with aluminum sheets, so it need not be shaped. Leave it flat.

This is an aluminum sign from a salvage yard, 1/8 inch thick. I scored it with an angle grinder cutting disc until it could be bent on the score.

Bending back and forth splits the sign into two equal halves.

Here, the shaped board has been coated with boat epoxy resin, and the two aluminum pieces have been drilled through while on the board. The holes are countersunk and screws attach the aluminum to the board. The aluminum still has to be cut to length. Note that you will have to measure the underside of your deck for the width, to know how long your alum. CB blade can be. Mine is a 30" deck, minus the two 2 x 6s (actually 1.5" thick), so I have about 27" to tuck my CB under the deck. I make the blade 26 3/4" and test it before any final touches.

The aluminum has been screwed to each side of the board, and a putty, made from wood flour and epoxy is spread to blend the edge of the aluminum with the board. The oak CB is in the background.

This is the putty stage. Mix wood flour (sanded wood) and resin to make a putty like peanut butter. Spread it on.

When the putty is hard, sand well to blend the edge. You will sand off some epoxy from the board, but you will coat it again later.

Since both CBs are nearly identical, I'll show next the stages with an oak plank 3/4" thick, half as thick as the other. I've already shaped it with planer and sander, and now I coat it with epoxy.

It has also been drilled for the aluminum. Moving right along...

Countersink holes, drip in some epoxy and then screw down tight. The epoxy will prevent water from entering through screw holes.

Both CBs now are completed the same way. Clamp the aluminum together, drill it and rivet. I used both 1/8 and 3/16. Smaller is better and easier to peen and smooth later.

The oak CB needed another piece of wood to make it the right thickness for the slot on the cat. Here I'm drilling out a 1/4" hole to a 1/2" hole where the pivot bolt goes.

With a keyhole saw, I enlarge the hole to maybe 3/4", making it quite ragged.

I know, it looks unprofessional now, but wait...

What you missed here you can see on the rudder update. I filled that ragged hole with epoxy (masking tape on the back first) and fibers, let it set hard, then drill the final 1/2" hole in the epoxy. This way, no wood is exposed to water and the hole is very clean.

See, nice hole. All of the CBs and rudders were done this way.

The oak CB ready to paint.

The oak CB I filled with camping-mat foam. The other I just made foam plugs for top and bottom (shown here) to keep the water from swirling inside. A hole in the foam is needed to let water in and out, otherwise it has to drain slowly later.

Both of these new CBs perform well. The best is the thicker one, and I have heard from a boatbuilder that it creates a more efficient underwater foil and aids in pointing and speed.

RebelCat 5 now points even better than with the original CB, and it was already quite good for a cat. The 2 x 8 was cheaper too. I made both so you could see the results. I now use only the cheaper one, because it performs so well.

See also the new rudders, done using the same design.