What is the best way to fix leaks on a pre-70s aluminum rowboat?

I had an aluminum boat at one time assembled with rivets. From all the pounding and flexing the holes enlarge slightly and the rivets loosen up. I had to go through and tighten every single rivet. It took two people, one to hold a hammer against the rivet and another to use a punch and hammer on the other to compress or smash the rivet back down again.

I have seen people use epoxy to patch leaks also.

A lot of boaters do not realize it but that is why a welded boat is well worth the extra money.

Where are your leaks? If you have small holes or seams that leak, you could try fiberglass mesh & resin on both sides of the hole or seam. You will need to rough up the surface of the aluminum with a heavy grit sand paper and then clean the area really well for good adhesion. When you apply wear latex gloves because this stuff is nasty sticky. It should bond great and be slighly flexable with the giving of the metal of the boat. It is sandable after it hardens, but wont look that great unless you paint over it. But I assume you aren't looking for beauty with that age and type of boat, just function.

If your holes are pin hole size or the seam is barely leaking, you could prep the same way but use metal epoxy on both sides, this too will hold up really well but probably wont hold too well on holes bigger than 1.5mm, good luck.

Put the boat in the water, locate the leak areas- they will be on seams. mark them with a marker.

take the boat out of the water, drill out the rivets in the leak areas. Carefully insert a small screwdriver to separate the two layers of aluminium, inject a small amount of silicone sealant, leave for a few minutes until it starts to cure, then re-rivet using monol rivets if possible. If you can't get monol rivets, dip ordinary rivets in nail varnish or hammerite paint

Being a heritage vessel, its important to maintain an authentic period restoration process.

The usual 70's solution was to use genuine Munz Metal Mastic

i.e. chew lotts'a gum ...

More palatable as a repair methodology before you have bait on your hands of course.

Maybe a fiberglass patch kit ?

http://www.westmarine.com/1/1/8007-aluminum-epoxy-... Don't mess around, do it right, if it can't be welded