What structure on a vessel allows a rope to be fastened?

The correct choice, which identifies the structure on a vessel that allows a rope to be fastened, is a cleat. A cleat is a fitting with projecting arms, usually found on the deck or sides of a boat, designed specifically to secure lines or ropes. When a rope is wrapped around a cleat, it can be held securely in place, making it essential for mooring the vessel or managing sails.

The other options offer useful features of a vessel but do not serve the purpose of fastening ropes. The gunwale is the upper edge of the side of the boat, the bow refers to the front of the vessel, and the hull is the main body of the ship, which houses all its components. None of these structures provide the functionality of securing a rope like a cleat does.