If you have a boat, you often have vinyl seats. If you have vinyl seats, you probably will be repairing or replacing them at some point. Seats and any exterior feature on a boat lives a very hard life.
This is a good set of instructions covering (pun intended) the basics of dealing with vinyl seats. The author also has some other posts up, including some on restoring an aluminum boat. He looks to be making more, so is definitely somebody to watch.