A Surface Effect Ship (SES) is a class of ship that has both an air cushion (like a hovercraft) and twin hulls (like a catamaran). When the air cushion is in use, a small portion of the twin hulls remain in the water. When the air cushion is turned off ("off-cushion" or "hull borne"), the full weight of the vessel is supported by the buoyancy of the twin hulls. A hovercraft, or air-cushion vehicle (ACV), is a vehicle or craft that can be supported by a cushion of air ejected downwards against a surface close below it, and can in principle travel over any relatively smooth surface, such as gently sloping land, water, or marshland, while having no... A traditional Tamil catamaran on a Chennai beach. ... In physics, buoyancy is an upward force on an object immersed in a fluid (i. ...

The SES has two clear advantages over a hovercraft for open sea operation: it is more resistant to slipping sideways when acted on by air or sea and; it can use water jets for propulsion as the inlet nozzles are always covered by water.

Two experimental SESs, both of around 100 tons, were developed for the US Military in the 1960s; the SES100a and the SES100b. They both attained speeds between 60 and 100 knots.

Currently SESs are used as small ferries and are rumoured to form the basis of a new generation of sea going cargo vessel, carrying high value cargo at high speeds on shorter cargo routes (such as Japan and Korea).

Royal Norwegian Navy built 9 MCM's SES, which 6 of them are in service.

The Norwegian Navy have also one prototype Littoral Combat Ship SES, KNM [1], the Skjold class. KNM Skjold's service speed exceded +55 knots. This prototype was also a year in the US for testing in the US Navy. The Norwegian Navy have orderered 5 more vessels from the ship yard-UMOE Mandal