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.

Final drive - well for now anyway

Building this boat seems to be a continual process of design and redesign.
The last couple of days I've been focusing on the drive, gettoi the power
from my feet on the pedals to the propeller. I thought I'd found the ideal
with Rick Willoughby's swing-arm double roller clutch mechanism till he
pointed out that the prop freewheels when you're not pedalling, and that
means you can't back-pedal. Back-pedalling could be important for
manoeuvring and also for unwinding any weed so I had to think of another
idea. So then I thought of some form of belt drive using steel cable, but
how do you join it?

Yesterday though I had the breakthrough (well I hope it is). I got to
thinking about the flat belt drives of the old cotton mills. They'd twist
and turn around the place so why couldn't I do the same? But what to use for
the belt that wouldn't stretch or slip? Nylon webbing seemed to be the
answer to the stretching, but the slipping? Then it hit me, Velcro! It's
very flat so easy to join, it can be stitched even, and if I used the hooked
side as the belt I could put the fuzzy side on the pulleys. I can even melt
stripes into it so that it becomes a fuzzy cog. That means that the peeling
off part as the belt comes off the pulley will be easier too. And it's easy
enough to make up my own pulley wheels to get just the gearing I want.

No doubt there's downsides I've not thought of. Possibly it's not the most
efficient system in the world, but as I'm not worried about 100% efficiency
that's not a problem. Perhaps it'll stretch or slip too much, well it's easy
enough to make up a test rig to find out. For now though I'm happy.

Now on to the next problem.

PS I've blogged this from my mobile, so excuse the typos, please.

Finally!

Well I finally seem to have got a design that could work. Over on the boat
designs forum, people much wiser than me have plugged in the numbers and
worked out a whole series of numbers which show she'll be reasonably stable,
and should, at a normal pedal do about 10 km/h. That's pretty good, as I've
always thought I'd do about 6 km/h on this trip, which with six hour days
meant I'd take ten days from one end to the other. This way I've got some
flexibility. In all this I have to thank Rick Willoughby, in Australia,
whose patiently explained things.

It's Rick too, who showed me what I'm almost certain will be the final drive
solution. He's used pedals on swinging arms connected to two roller clutches
as a way to twist the drive through the 90 degrees. It looks like a good
reliable and cheap solution. All I have to do is find the roller clutches.

So that's where Voie Bleue stands at the moment, a finalised shape - which
will no doubt change as the build goes on, and a drive system where I have
to find the parts. Not too bad, now I really want to get on and build,
before summer really comes.