Minecraft wiki entry for Boat_with_Chest, associated text: The inventory of the boat with chest has the same amount of slots as a single chest. Its inventory can be accessed by sneaking and interacting on the boat with chest, interacting on the boat with chest while a player or entity is inside the boat[verify], or by opening the player's inventory whilst inside the boat. This means that the player cannot access armor or offhand slots without exiting the boat.