"Phil Kangas" wrote in message
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"Bob La Londe" wrote in message
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"Steve W." wrote in message
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Bob La Londe wrote:
I have a copy of Pollards aluminum boat building book, and I have read
it.
It looks like he mostly plans on boats to be all cut pieces and welded.
That's great for big boats or even for some small boats, but braking
seems
like it would make more sense if you have access to a brake big enough.
Some of the small boat designs (think shallow draft skinny water boats)
would really benefit from a mostly bent hull. Aluminum sheet can be had
in
pieces large enough to make most of a hull out of one sheet. Some
cutting
and welding is still needed obviously, but if you could brake the keel,
chines, and bottom of the transom only welding the front and the sides
in
the back you would have an inherently stronger and more rigid boat for
rough
service.

The problem of course is how do you brake a piece of metal that big?

Yeah I know a giant hydraulic brake would be a good answer for the
commercial boat builder once they have the capital for it, but how does
the
backyard boat builder do it? Are they stuck with all cut and welded
pieces,
or hauling their sheet to somebody with a giant brake to do it for them
(if
there even is somebody with a brake big enough in the area that hires
out)?



I think the main reason is stress on the hull. The cut and welded seams
will be stronger and take the constant bending better than a simple bent
section of aluminum. Keep in mind that all boats flex small boats flex a
LOT. Aluminum doesn't like flex but with the cut sheets the flex of each
panel can be dissipated better than if you used a single piece. Plus
since many of the pieces come together over
frame sections the cut sheets get welded to the frame and each other in
the same step.

Commercial boat builders (in some cases using what I would consider the
wrong alloy) make long brakes in aluminum all the time. Most small boats
have rolled or bent ribs in the hull for strength.


What alloy?

5052 seems to be the most popular alloy for hulls, with some builders liking
5086 for structural components, and very much so for larger boats. Some of
the backyard mud boat guys are talking about using 5086 for hulls as well
for its greater strength. I'm not sure its all that much gain in thin hull
material, but...