Yeah, what Lou said...
There are actually many kinds of rivets. Most used in boats are solid and get "hammered" to compress them. Usually the aluminum rivets used in boat building for above the water have rather large, pan heads. The flat head variety require a special drill to countersink the head. Those are usually fairly specialized. Most decent quality aluminum boats have those along the bottom.
You would match the rivet diameter with the hole dia. I think you probably would want the rivet length to be at least twice the thickness being fastened.
If you are talking about rivets with the "rod" in them, those are "pop rivets". They require an inexpensive special tool or "gun" as it's more commonly called. These ARE NOT waterproof, although I've read and heard of some you can buy that are advertised as being "waterproof". I wouldn't trust them in a boat.
I hope this helps explain what I mean. I'm sure there are guys on here who are a little better versed with words who can explain a little better.
If the round head variety will work, let me know...
Jon