When you think about it, aluminum boats are little more than a few sheets of metal, held together with some rivets and welds. And while it’s pretty amazing how much of a pounding they can take, eventually their rivets loosen or break—and then the seams on your hull may refuse to keep the water in the lake, where you want it.
To find the leaking culprits, let water in from outside, or let it out from inside: You can beach your boat and gradually, foot by foot, slide it into the water, marking the rivets that leak as you move along. Or, get the boat up off the ground, fill it to the water line with water, and mark the leaking rivets.
To rebuck (tighten) a rivet, you’ll need a helper (or long arms). One of you holds the buck—any anvil-like hunk of steel—tightly against the flat side of the rivet, while the other hammers the crimped end. If you have one, an automotive bodywork dolly will work as a buck, and a ball-peen hammer can retighten the rivet head. You can also use the face of a sledge hammer as the buck and a carpenter’s hammer to tighten. The key is to avoid too much hammering: Old aluminum rivets can split or break if you give them a heavy whack.
When that happens, you’ll need a source of solid aluminum rivets. Check marine supply houses and sheet metal vendors. To remove an old rivet, file or grind off one head, or drill it out, but don’t enlarge the hole. When seated in its hole, the new rivet’s unpeened (headless) end should protrude by about 2/3 of its diameter. For the best hold, “set” the rivet first, so the metal sheets are in tight contact. Drill a hole just larger than the rivet’s diameter in a hardwood dowel or steel bar. Put the rivet in its hole and your buck against the rivet head. Slip the dowel over the unpeened end—a solid hammer blow will cinch everything up, ready for you to shape the rivet head.
Can you use pop rivets instead? You only need access to one side of the hull to install them, but standard pop rivets are useless below the water line—they have a hole right through them! If you can’t reach both sides, you can try a closed-end pop rivet. It’s not a typical hardware store item, though, so be prepared to hunt around.
As a stopgap until you can install a new rivet, you can also use a small stainless steel machine screw with an acorn nut. Flexible marine epoxy or sealant, applied to the hole before tightening, will help this repair last longer.