Minecraft wiki entry for Shipwreck, associated text: Shipwrecks contain up to 3 loot chests, depending on the sections still intact. Supply chests generate in the bow of the ships, treasure chests generate in the upper section of the stern, and map chests in the lower section. In the case of certain shipwrecks, especially those that intersect other structures, the chests that would normally be present in the corresponding section may be absent, resulting in some shipwrecks holding no chests at all. Although chests don't usually generate for missing sections, map chests from shipwreck sterns may generate in upside-down bows even if the stern is missing. Furthermore, each shipwreck with at least 2 chests always contains its map chest.