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>RebelCat 5 Update 10-27-09
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...
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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. |
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Using a jigsaw, I cut the rough
shape of the CB. |
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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. |
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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. |
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Bending back and forth splits the
sign into two equal halves. |
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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. |
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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. |
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Spread the putty smooth to even out the edge
of the aluminum. The screws have already been
put in to hold the aluminum to the board -
notice the putty in the countersunk holes over
the screw heads.
If you look at the top part of the CB (at
the bottom in this photo), you see that I got
carried away while shaping the edge of the
wood. The top should be flat at the top where
it will fit inside the CB trunk. Fortunately, I
left the other side flat, so the CB doesn't
wobble. Shaping the trailing edge of the CB
above the aluminum is not needed.
In the background is the CB made from an oak
plank. It has already been painted.
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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.
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The oak plank has already
been drilled for the aluminum. Here, it is
coated with epoxy resin. |
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Countersink holes, drip in some
epoxy and then screw down tight. The epoxy will
prevent water from entering through screw
holes. |
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Both CBs now are completed the
same way. Clamp the trainling edges of
the aluminum together, drill both and
rivet. I used both 1/8 and 3/16. Smaller is
better and easier to peen and smooth
later. |
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The oak CB needed another piece of
wood laminated to it at the top to make it the
right thickness for the CB slot on the cat.
Here I'm drilling out a 1/4" hole to a 1/2"
hole where the pivot bolt goes. |
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With a keyhole saw, I enlarge the
hole to maybe 3/4", making it quite
ragged. |
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I know, it looks unprofessional
now, but wait... Actually, the more rough and
ragged you make this hole, the better it will
be for the next step. On the rudders, I
actually cut slots around the hole, making it
look like a sun icon. |
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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. |
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See, nice hole. All of the CBs and rudders
were done this way. If a 1/2" pivot hole is
drilled in the wood directly, water will cause
the wood to swell, making it difficult to
remove the pivot bolt later.
Wet wood also tends to rot sooner or later.
By making a larger hole in the wood and filling
it with epoxy and fibers, then drilling the
1/2" hole, water never reaches the wood, and
the hole is precise.
I'm not sure, but I might have invented this
technique.
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The oak CB ready to paint. The
aluminum has been trimmed to match the wood and
riveted on the trailing edge. |
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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.
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| See also the Update on the new
Rudders here. |
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