From the publish's website:
This full-color, double-sided Dungeon Tiles sheet portrays both the main deck and below-deck areas of a longship, a pinnace, rowboats, and more! Each DM that scheduled and reported five sessions of play between January 1 and June 30, 2009 received two copies of the tile sheet – enough to run a longship-to-longship combat or create a layout showing both main and lower decks simultaneously.