the difference...<br/><br/>you could certainly bless the ship in its entirety..  this takes a simple component we have and your characters have salt.. :)<br/><br/>the rooms under the deck are certainly able to be protected in this manner (the demon could not have moved through you door.)but do remember this is a ship and it moves, on the ground i would say you could draw your salt circlees and protect the ship, but the stuff will simply blow off once you start moving... you can also cast "protection from evil 10' " but it will only protect the ship for the running time of the spell, besides if he has a ship, the ballista bolts and catapult rocks arent anything that can be protected from :)<br/><br/>so sure protect the rooms and lower decks anyplace the salt wont blow off :)