Semi-submersible ship, also known as semi-submersible mother ship, is a special marine ship that specially transports large offshore oil drilling platforms, large ships, submarines, gantry cranes, prefabricated bridge components and other super-large equipment that cannot be hoisted alone.

For example, the semi-submersible "Tai 'an Kou Wheel" in China, the loading platform is like a football field. When loading and unloading large floating cargo, the loading platform can dive 19 meters, and the depth of the loading platform is 9 meters. Total length156m, profile width 32.2m, profile depth10m, and load capacity18000t.