Today's theme is bottoms and tops. First, the finishing of the bottom and the application of a graphite/epoxy
mix. Then some work on the hatch and the final installation of the coaming.
The theory behind a graphite/epoxy bottom is to take the standard epoxy and to make it so slippery that rocks, oyster
shells, glass, gravel, etc. do not get a purchase in the surface and so are unable to start a gouge. Graphite/epoxy
is not a "bulletproof" hard surface, as I've seen it described so often by folks who confuse it with aerospace graphite
composites. It is, in fact, somewhat softer than plain epoxy, but much slipperier.
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Filling the weave
Since the bottom will be covered by the graphite/epoxy mix, I filled the weave with a thick slurry
of phenolic microballooons and epoxy. This let me economize on the epoxy, while yielding an easy-to-sand
surface. The horrible purple color will be covered by the graphite.
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Hull masked
Once the bottom was filled and sanded, I masked the hull with fine line tape. I used the tops of the stitch
holes on the side panel as my boundary line. Not only does it actually make sense to protect the seam, but it
also covers all the holes and joints.
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Black bottom I
I used a 50/50 mix, by volume, of graphite and mixed epoxy/hardener. The epoxy and hardener need to
be thoroughly mixed first, then the mixture is slowly poured into the graphite. It's like mixing cocoa
powder and milk - adding the powder to the milk gives a lumpy mess while the reverse order gives a smooth
paste.
Graphite powder starts flying with the slightest puff of air. It also stains anything it touches dark
black. Definitely wear gloves and eye protection and at least a dust mask, as well as old clothes.
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Black bottom II
Once the goop is mixed, just pour it onto the bottom and spread it with a short nap roller. Tip it
out with a dry foam brush to get rid of the air bubbles. Two coats should be plenty. Unsanded it will
be a striking glossy black with a slight orange peel finish. Sanded it will be a smooth pencil lead grey.
I didn't sand mine. The graphite is effective UV protection, so there's no problem with leaving the
bottom exposed to the sun.
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Hatch straightening
My hatch cover ended up with a lengthwise curve which made it bow up when in place on the boat. So I
cut a kerf laterally across the doubler, clamped the cover to a flat workbench, filled the kerf with
epoxy/woodflour mix and glued a longitudinal stiffener to the doubler. The stiffener and hatch form
a t-beam, which strongly resists bending. The operation was successful, reulting in a perfectly flat hatch
cover.
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Hold-down hardware
These are the bits needed to make an internal bungee hold-down system. There are 4 bungie loops (the
D-shaped bits drilled for the bungie cords) and two hooks. The bungie loops are cut from 1 1/4 inch hardwood dowel
that's been drilled and had a flat side planed on it. They go into the hatch compartment. The hooks are cut
from plywood and attach to the bottom of the hatch cover.
For those who don't want to take the trouble to make their own, CLC sells a kit with lovely trapezoidal
drilled bungie blocks and tacky metal hooks for $35.
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Bungie loop in place
To install the bungie loops, rough up the surface in the hatch compartment and simply bed them in
epoxy/woodflour putty.
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Last bits
This image is quite a milestone - all the wooden bits are used up. Everything in the kit
box has been attached. There are only 2 pieces now - the boat and the hatch cover.
In the foreground, the hatch cover has received its bungee hold-down hooks, which are held
in place with masking tape while the epoxy is curing. (The stiffener
bar has also been smoothed.) In the background, the coaming is held in place for its final
cure with every spring clamp in the shop.
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