Does it not already have one?<br /><br />I've heard of people drilling a hole in the transom of their boat and then welding in a peice of copper tubing that a drain plug will fit in.
I put one in an old glass GameFisher. Just drilled a half inch hole and used a lever type plug. Never leaked. With aluminum, it may be too thin?<br /><br />Probably don't need it if it's still a "row" boat.