TYPE DESCRIPTION ADVANTAGE DISADVANTAGE
Mitre Gates Consists of a pair of gates hinged at the dock walls. The gates swing open horizontally. • Fast operating

• Creates heavy loads on floors
• Operating mechanism is costly & requires costly maintenance.
• Major repairs require removal of gate.

Flap gates Consists of a rigid one-piece gate hinged at the bottom that swings downward and outward. • Fast operating • Creates heavy loads on walls
• Operating mechanism is costly & requires costly maintenance.
• Major repairs require removal of gate.
• Recesses must be built into walls to maintain clearances.

Sliding or Rolling Caissons These are built up box sections with a sliding or rolling surface at the base.
The gate slides or rolls into a notch built into the side of the dock. • Fast operating • Cleaning and
2.2 – FLOATING DRY DOCKS

Floating dry docks are structures with sufficient dimensions, strength, displacement and stability to lift a vessel from the water using buoyancy. They generally follow a similar structure to that of a pontoon, although they have a cross-sectional shape of a “U”. The walls of a floating dry dock give it stability when the floor or deck is below the surface of the water. When valves in the pontoons open, the chambers in the dock fill with water causing the dry dock to semi-submerge itself under the water allowing a ship to be moved into position inside. Once the ship is in position, pumps start up and pump all the water out of the chambers floating the dry dock back above the surface. Floating docks can be built to almost any specification, although the most common range in lift capacities is about 1,000 tons to well over 100,000 tons as this is the most economical