"Bob La Londe" wrote in message
...
"Phil Kangas" wrote in
message ...

"Bob La Londe" wrote in message
...
"Steve W." wrote in
message
...
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...


The 5xxx series are work hardening, the more abuse
the better. A few
years ago I repaired a canoe made in the 50's that
was knicked by a snowplow.
It sure was tough stuff! Almost like stainless, it
was so tough! ;)}