I''ve been working in the metals trade for more then 30 years and I thought I would rely a few problems of welded aluminum.
I have also been consider an alum. vessel for my next venture so I''ve been looking at all the alum. boats that come my way.
First you''ll need to know is that 5083 is marine grade alum. with a 4.5% magn. content. Sometimes 5056 is substatuted but the weldablity is less desired. When welding alum. the properties in the metal change creating a weak area around the weld, a softening of the metal. There are three ways to weld alum. Mig - a wire feed gas sheid electric weld. Tig -an AC electric arc gas sheild with alum rod added as needed. And electrtode welding rod flux coated. Tig is the strongest but very time consuming. Mig is acceptable and the most common. Electrode not even considered for boat construction.
Any high stress areas should be formed rather than welded. On the vessels I''ve inspected with cracks, the cracks were around stantions, in the corners of transoms, cabin to deck mountings and deck to bulwark mountings. All the cracks were just outside of the welds in high stress areas. Theses were all powerboats, I haven''t had the opportunity to check out a sail vessel yet. So I''m sure around deck fittings and rigging mounts would need a good inspection.
Alum boats are built like steel or wooden boats with frames and a keel beam which in the thinner hulls you''ll see a weld seam at each frame, a bulge in the surface.
As for painting, the surface will need an acid etching for the paint to stick. And below the waterline I would use an epoxy bottom kote.
The nice thing is if you want to fill a hole or do some patch work, it can just be welded up. On larger vessels one could carry their own welding machine.
Enough for now...................._/)