Surface effect ship

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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.

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.

The United States Navy initiated the SES model test program in 1960. By 1963, a 10-ton test craft called the XR-1 was designed and built to test the surface effect concept. The first version of the XR-1 used fixed plywood seals at the fore and aft ends of the captured air bubble section. A jet engine providing 1700 pounds of thrust was used for main propulsion. A separate 110 horsepower gas engine was used to drive lift fans, and also to power out-drive units that were used for off-cushion slow-speed maneuvering. During the first year of testing, the XR-1 was fitted with more powerful main propulsion and flexible fore and aft seals were test, as well.

The XR-1 was also used to test the concept of water-jet propulsion. The ship was modified in 1964 and equipped with gas turbine engines driving the water jet propulsors. The ship's weight increased to 17 tons.

Rohr Industries became involved in SES history in 1970, taking over the XR-1 test program for the navy. Rohr continued to use the XR-1 to test propulsion and seal concepts. Their eventual goal was to develop a 3000 ton SES capable of utilizing vertical launch missile systems and anti-submarine helicopters. The proposed ship was to be capable of 90 knots in sea-state 6 conditions. The proposed main power units were to be 4 40,000 hp gas turbine engines driving water jet propulsors. The 3000 ton ship development contract was canceled in 1980.

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. The SES 100B achieved speeds of 100 knots, approximately 110mph, on Lake Pontchartrain, north of New Orleans, Louisiana where it was built by Bell Aerospace/Textron Corporation at the NASA Michoud Assembly Facility. The 100A ship was used to test waterjet propulsion and automatic ride control systems. The 100B was capable of operating almost completely out of the water on an air cushion with only the propellers, mounted on retractable shafts, entering the water. The 100 ton SES 100B was built for the US Navy as a 1/10th scale model to test the feasibility of using hovercraft and other Surface Effect Ships in combat situations. The top-secret specifications called for a ship capable of entering a combat zone at a speed of over 100 mph and disgorging a tank and 100 soldiers onto a beach, turning back out onto water and escaping at high speed. The SES ships are the prototype vehicles for the LCAC's used by the Navy with such success in the Persian Gulf War.

(The 3000 ton SES concept was never designed to go up on the beach, like a landing craft. The LCAC and the SES were very different concepts from the beginning. The LCAC (landing craft, air-cushioned) is a pure hovercraft that is capable of high speed insertion of troops and vehicles onto a beach. As a hover craft, the LCAC has no rigid hull parts that extend past the air cushion. The SES has rigid side hulls that extend below the air cushion, precluding it from conducting amphibious operations. Design concepts for a 6000 ton cargo SES that Rohr was also proposing relied on the idea of the ship loading and unloading from conventional dock facilities.)

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 exceeded +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