We know a Camel as the ship of the desert, but a Ship camel is an external floatation tank that is fitted to a ship to increase the buoyancy or reduce her draught.
There are many types of Ship Camels. Simplest are floatation tanks with additional vice like devices that can hold the ship. These devices reduce the draught and allow its repairs or allow it to negotiate waters of low depths. The Ship Camels inner walls are concave and curved so that they embrace body of the hull of the ship. The ship camel is partially sunk using ballasts, installed on ship, and water is then pumped out. The increased volume provided by the Ship Camels allows for the system to float in a reduced draught.
The Ship Camels were once used by the Dutch for accessing the shallow waters at Pampus, which were unreachable for large merchant ships. Instead of a real ship camel, sometimes light (sailing) ships were used to lift a ship.