primer

I am about to primer my boat, and was wondering if I had to have the boat down to bare metal or just give the old paint job a good sanding. All I have to sand is a little sander that would take days to get down to bare metal.

Its personal preference, but if your paint is in good shape (no peeling), then I would rough up the surface and continue on with the project.

1. If you go to bare metal, a self etching primer is needed to "bite" into the aluminum.
2. If you just rough up the surface, a standard primer should do just fine.

So, if you decide that your paint is adhered well, and you don't have any leaks, then:

-Rough up the surface
-Spray it down, or give it a good wipe with some acetone
-Hit it with your primer
-Then put down at least a couple of top coats

Exactly what Meanmouth said.