So to clear up some potential confusion, a "galley" is a particular type of ship that's propelled mainly by oars -- the replica Greek galley Olympias is one example of this type. There wouldn't have been galleys in the Caribbean in the 18th century, although some European powers did maintain galley fleets in the Mediterranean.

Anyhow, the lifespan of wooden ships is something I've written about before. It really depends on how well they were maintained and what they were used for, and how long -- how long will a modern car last if you don't change the oil or top off the fluids? But a ship used in the Caribbean would definitely have a shorter lifespan, all other things being equal, or require more maintenance, than one primarily used in the North Atlantic or the Mediterranean, due to the warm water of the sea. The shipworm (teredo worm) was a particular danger to ships in warm waters, and before lead sheathing and later copper sheathing was in wide use, shipworms wreaked havoc with wooden ships. The warm Caribbean water would also facilitate the growth of marine organisms on the hull itself (algae, weeds, etc) that would slow down and further burden a ship, and would have to be scraped or burned off by careening or docking the ship. I wrote about coppering more here.