On Fri, 30 Dec 2011 12:22:53 -0700, "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)?

What kind of boat are you planning to make? A jon boat made of
aluminum typically has lots of longitudinal "stringers" bent into them
with a roll-forming tool, or added-on stringers made of bent aluminum
channels that were then riveted on. We had one of those when I was a
kid.

Small conventional pointed-bow boats traditiionally are formed either
by stretch-forming (used also for canoes) or with big drawing rigs to
pull the sides of the bow together. Then they were TIGed (heliarced,
actually). Today, I understand, they're MIGed.

Without componnd curves, aluminum is too floppy for a boat. When they
draw it into curves, which are simple curves, they generally back it
up with riveted stringers or those rolled-in equivalents.

I watched them stretch-form aluminum boats at the old Fairchild
Aircraft factory in Hagerstown, MD in 1957. My dad had contracted with
them to build boats for Sears after they lost some aircraft contracts.
At the time I didn't know what I was looking at, but after working at
American Machinist for a couple of years, I realized that I had been
watching a stretch-forming operation.

--
Ed Huntress