Dead Ahead -- straight in front of

Dead Astern -- straight behind

Deck -- the horizontal and permanent portions of a ship’s structure  

Dinghy -- Smaller boat carried or towed behind a larger craft usually for emergency purposes

Displacement -- the weigh of water shifted by the boat’s presence in the water, used to measure a boat’s weight

Displacement Hull -- A “Hull” which pushes away an amount of water equal to its weight, regardless of speed or power

Dock -- Man-made area where boats are “Moored,” usually has a means of controlling the depth of the water

Dolphin -- A circular structure of “Piles” driven into the sea bed and bound with line to create a secure platform where extending the “Dock” wouldn’t be practical

Draft -- The depth of a ship’s keel in the water