If you want to make it like new (no paint) you will have to have it soda blasted, then painted with a barrier paint then a top coat.
If you are going to leave in any water you will need to paint it.
If what you have is 30 coats thick like mine was, then have it soda blasted then barrier painted and a new bottom paint added.
I used West Marine ablative paint, not sure how much? $110 ?? But that will last you years!
http://wellcraftv20.com/community/sh...ighlight=paint