What Is a Manhole Cover? Definition, Meaning and Concept

A well deck is a deck on the rear of a ship designed to be periodically filled with water to allow launching and recovery of vehicles. This design feature is often seen on ships designed for amphibious warfare, as well as some scientific and industrial ships that need to be able to launch vehicles and equipment. This design adds complexity to the ship's overall engineering, as it must be designed to absorb water to lower the well deck and flood it for launch.

When not in use, the well deck is kept closed and dry. Staff can use it for activities such as calisthenics, machining, etc. during dry spells as it is generally a large, level space. Equipment destined for the launch is also stored in this area, allowing personnel to perform maintenance and other activities as needed. This may include repairs while a ship is underway, to allow damaged equipment to be relaunched.

For launches, the ship takes on water and opens the doors to the well deck, exposing it to the sea. Boats can float off the surface and be launched, while staff can drive cars and trucks for activities like beach landings. A ramp can be provided to facilitate unloading of wheeled equipment. Helicopters, weather balloons, and similar equipment can also be launched from a well deck.

This deck is similar to a hangar, and can vary in size and shape. Large ships may have a very substantial amphibious transport hanger along with troop accommodation and support equipment. The ship can move troops and equipment to where they are needed, open the well cover, unload and wait for them to return. Once everything is loaded again, the ballast tanks can be emptied to allow her to rise, bringing the deck above the water level.

The design of ships of this nature needs to accommodate ballast tanks, the well deck and any ancillary equipment such as door controls. Engineers must also consider the potential loaded weight of the vessel when the vessel is fully loaded, and what could happen during flooding of the tanks. It is critical to have enough freeboard to keep the ship afloat and prevent sinking in heavy seas. If too much of the hull sinks underwater, the boat can become unstable and strong winds or large waves could pose a threat.