Ship bound adventures

I have always thought this is the single hardest enviornment in which to run an adventure. The issue I have with ship bound adventures is how to deal with the long hours, days and weeks of plain sailing? It always feels to me that as soon as you mention a sail on the horizon the party leap into battle readiness because as a GM ou would not have mentioned it otherwise and besides they are adventurers and these things happen to adventurers.

How many times can you attack a ship with pirates, sea monsters, flying monsters and hurl it into natural storms, maelstroms and so on before the crew will be throwing the party overboard?