Thursday, June 14, 2007

Bend me, shape me, anyway you want me

I've had my song in my head all night, and it certainly seems appropriate as
I'm thinking about the hull construction. Again it's a tale of options, and
going through the pros and cons of each one.

I started with "tortured PVC" the idea being to take large 2m x 1m sheets of
PVC and bend them over a skeleton then fill the whole lot with expanding
foam. I moved away from that to the foam sandwich idea.

The foam sandwich would be 40mm sheets of expanded foam each cut to follow
one of the contours of the boat. Then they're all laid one on top of each
other and given the final shaping. Once the hull shape is there the whole
lot is covered in fibreglass and epoxy. But then yesterday I discovered a
new method.

This one involves building an "external framework" which matches the ull
shape.Then, thin, rollable expanded foam is laid inside this and glassfibre
and epoxy applied. Once it's all dried you pop it out of the framework and
glassfibre the outside. The idea is that each half hull can be built in the
same framework, simply by flipping the framework round.

So which one to do? I'd discounted the tortured PVC as the curves began to
get a bit complex and I found that PVC sheets were smaller than I thought,
but then I discovered that the expanded foam is much more expensive than I
though, it also involves huge amounts of cutting and sanding and there's the
problem of mounting the pedal and seat frameworks. The external framework
looks interesting, the foam's readily available, but I'm worried about how I
could keep the hull form in place during the build up.

So I'm wondering again about tortured PVC. First of all I've found that I
can get PVC in bigger sheets than I thought and have read more about
thermoforming, secondly I like the idea of the finished hull being in large
sheets, somehow to me it seeems more abrasion resistant, thirdly the egoist
in me likes the idea of using a method I'd though of myself, and finally
I've realised that the curves, whilst more complex are also larger than I'd
been thinking of.

So yet another change, and for now I'm going to look more at the PVC method,
but with a twist. I'll still have the internal framework, but I'm thinking
that combining that with parts of the external frame male mold, to help the
thermoforming process.

Watch this space, as they say.