I hesitate to suggest this in relation to boat building except that you
might be able to make some difficult shapes with this technique. (and
create hard points)

Braking aluminum can be a real challenge. Especially if you want to make a
sharp corner in a long piece of sheet. A brake that will handle an 8' piece
of .125 is gonna cost some serious bucks. More than the average backyard
boat builder is going to want to spend. (never mind the wealthy tool whores
or that I would have one if I could afford it)

I have used this technique for making some support angle in other than 90
deg applications. I've only done this with .125 5052. The longest bend I
have made this way so far is about 3 feet. Cut the sheet half thickness
along a line. I used my table saw to do this. Clamp the sheet to a rigid
surface. I used a cast iron table saw and a piece of 3/8 angle iron. I
also clamped 1/4 aluminum plate to the free side to help keep it rigid and
straight. Bend in a moderately fast single motion to the desired angle.
Depending on what angle you are trying to reach and the size piece you are
working with this can be easier than you think.

At this point I hade a piece with a very nice small radius outside bend, and
the angle I desired. I made several pieces like this for one project that
had an inside angle of about 70 degrees. Of course the piece is very weak
at this point (thickness) and very hard (work hardening) along the bend.
Its almost impossible to bend it again if you didn't get it right the first
time. Instead you wind up distorting the legs of your angle.

Lets assume the piece would be at the correct angle at this point. Then I
took a good stainless brush and polished the inside of the angled and then
welded a bead right down the inside. No worries about air contamination
since there is no opening to the other side. No back chipping necessary.
If you get your rig setup just right you will see you can get almost perfect
penetration by looking at the other side. It welds very fast, and each
piece is trapped to the other piece by the remaining portion of the cut
groove.

I experimented a little with different pieces at this point. Some I lock
stitched and back filled and others I just welded as fast as I could go
(once I got dialed in for the heat and the thickness) from one end to the
other. Eyeballing with a good straight edge both pieces came out pretty
square and straight. I would probably still stay with the lock stitch and
backfill technique because there might be hidden stresses in the metal you
just can't see without some more involve testing.

Ok, you might ask. "You used this technique to make some non critical
support brackets. What is the big deal?"

The temptation.

Think about a blue printed fiberglass racing pad... like on a modern bass
boat. Oh!

Yeah. Now you see the point. You could make a really sharp square racing
pad this way out of aluminum. Sharp edges on a pad means fast. Some of the
guys who race boats like this have the edges of the pad so sharp they will
almost cut you. That sharp a corner would not be possible even with this
technique, but it would be a thousand times sharper than you could do on a
sheet metal brake.

Now comes the part that makes me scared to try this technique. By making a
sharp corner like that you are creating a hard point. Is the weld on the
inside going to account for that. I don't know, and I don't know how to
find out. It is certainly a very critical location on the boat. Its
taking all the force of running and pounding and flexing of the entire boat.
The only thing under more stress is the transom which at speed is carrying
the entire weight of the boat suspended in the air.

I suppose you could use a v-groove cutter on a router to get a better cut
with thicker aluminum. Obviously the technique would need to be adjusted
and modified based on material thickness, angle, desired size of weld bead
etc...

You might argue you could just corner weld two pieces of sheet together and
for some shapes you would have no choice. (curve along a line) There are
some things about corner welding two pieces. To do a perfect job you need
to weld it twice for one thing. Weld the inside. Back chip the outside,
and then weld the outside. You are going to get some distortion of your
associated planes. You are going to get a lumpy weld (by comparison) not a
nice clean sharp corner. Although I suppose you could over weld and build
up your bead and then grind back to square. I have done a couple pieces
this way also just to see what I would get. For small stuff you could not
tell, but with my level of skill as a welder I could see some distortion in
the sheets only as long as 2 or 3 feet when I threw my straight edge on
them.

I have had this process floating around in my head for a year. Now its time
for you to tear it apart.