After a bit of research I was a little confused. According to my research you can use sink as a sacrificial anode for Al depending on the exact alloy you are using.

Owners of aluminum boats make guests empty their pockets of loose change, because a penny in the bilge of an aluminum boat will punch a hole in the hull. I did make a mistake; has to be an old style copper penny for maximum galvanic corrosion.

It's a fairly lousy material for boats, though people use it anyway.