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{{Short description|Watercraft with air cushion and twin hulls}}
{{Refimprove|date=May 2019}}

A '''surface effect ship (SES)''' or '''sidewall hovercraft''' is a [[watercraft]] that has both an air cushion, like a [[hovercraft]], and twin [[hull (watercraft)|hulls]], like a [[catamaran]]. When the air cushion is in use, a small portion of the twin hulls remains 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.<ref>{{Cite web | url=https://www.foils.org/wp-content/uploads/2018/01/HCH1962Jul.pdf | title=Hovering Craft & Hydrofoil | website=www.foils.org}}</ref>
[[File:Skjold-class patrol boat KNM Storm.png|thumb|P961 Storm, a [[Skjold-class corvette]] of the [[Royal Norwegian Navy|Norwegian Navy]] is a modern SES, the fastest combat ship class afloat at the time of their introduction.<ref>{{cite web|last1=Lundquist|first1=Edward H.|title=Skjold-class Surface Effect Ship HNoMS Steil|url=http://www.defensemedianetwork.com/stories/skjold-class-surface-effect-ship-hnoms-steil/|publisher=Defense Media Network|access-date=2 December 2022}}</ref>]]
The SES has two 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 since the inlet nozzles are always covered by water.

== History ==
=== United States Navy ===
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 [[Wiktionary:fore#Adjective|fore]] and [[Wiktionary:aft#Pronunciation|aft]] ends of the captured air bubble section. A [[jet engine]] providing {{Convert|1,700|lbf}} of thrust was used for main propulsion. A separate {{convert|110|hp|abbr=on}} [[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 tested 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 1970 to 1980 ====
[[Rohr, Inc.|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 (3,050 tonne) SES, the ''LSES'' (''L''arge ''S''urface ''E''ffect ''S''hip) or ''3KSES'', capable of utilizing [[Vertical launching system|vertical launch missile]] [[Mark 41 Vertical Launching System|systems]] and [[anti-submarine]] helicopters & various [[VTOL]] aircraft. 

The proposed ship was to have a length of 270 feet and a beam of 105 feet The proposed main power units were to be four [[General Electric LM2500|LM 2500]] gas turbines, each driving an [[Aerojet]] [[Pump-jet|water jet]] propulsor. A cushion height of 18 feet was to be generated with two LM 2500 turbines driving six Aerojet centrifugal fans. It was to carry a crew of 125.<ref>{{cite magazine|magazine=Maritime Reporter and Engineering News|title=$3-Million Surface Effect Ship Award to Philadelphia Gear|page=24|date=15 November 1977|publisher=Maritime Activity Reports|access-date=19 October 2024|url=https://magazines.marinelink.com/Magazines/MaritimeReporter/19771115/content/3million-surface-philadelphia-210890|issue=22|volume=39}}</ref>

The 3000-ton ship development contract was canceled in 1980.

==== The SES-100 ====
[[File:SES100B 394.jpg|SES-100B during testing on St. Andrews Bay 1975|thumb|right]]
Two experimental SESs (the SES-100A and 100B), both of around 100 tons, with {{Convert|80|ft|abbr=on}} length and {{Convert|40|ft|abbr=on}} beams, were developed for the US Military in the 1960s and 70s. They both attained speeds in excess of the program goal of {{Convert|80|knot}}. 

The SES 100B, was built by [[Bell Helicopter|Bell Aerospace]] ([[Textron]] Corporation) at the NASA [[Michoud Assembly Facility]]. It had three lift fans powered by 600 horsepower gas turbines, and two 3.5-foot semi-submerged, [[Supercavitation|supercavitating]] controllable, reversible propellers each powered by a 4,500-horsepower gas turbine.<ref name="popscijun74">{{cite magazine|first=Ben|last=Kocivar|date=June 1974|magazine=Popular Science|title=75-Knot Ocean-Going Surface-Effect Ship|access-date=18 October 2024|publisher=Times Mirror Magazines|url=https://books.google.com/books?id=iFzpLpXjYdkC&dq=SES+100B+gas+turbine&pg=PA90}}</ref> achieved speeds in excess of {{Convert|96|knot}} in the [[Gulf of Mexico]] outside [[St. Andrews Bay (Florida)|St. Andrews Bay]] in [[Panama City, Florida]].

The speed was verified by the [[United States Air Force|USAF]] ARIS radar. It also fired the Navy's first vertically launched missile (an [[RIM-66 Standard|SM-2]]) while doing {{Convert|60|knot}}. It was also used to test automatic ride control and high speed collision avoidance and navigation systems. The 100A ship was used to test [[Pump-jet|waterjet propulsion]], variable geometry inlets and automatic ride control systems. The 100A and 100B were both capable of operating almost completely out of the water on an air cushion with only {{Convert|18|in|cm|abbr=on}} of sidewall, the propellers or the waterjet inlets entering the water. The 100-ton SES 100B was built for the US Navy as a 1/10 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 {{Convert|80|knot}} and disgorging a tank and 100 soldiers onto a beach, turning back out onto water and escaping at high speed.

Unlike the hard sidewall SES's, the full skirted AALCs, JEFF A&B were the prototype vehicles for the [[Landing Craft Air Cushion|LCAC]]'s used by the Navy with such success in the [[Gulf War|Persian Gulf War]]{{Citation needed|date=March 2013}}.

The 3000-ton SES concept was never designed to go up on the beach, like a landing craft. The AALC (Amphibious Assault Landing Craft) and the SES were very different concepts from the beginning. The AALC was a pure hovercraft that is capable of high-speed insertion of troops and vehicles onto a beach. As a hovercraft, the LCAC, derived from the AALC has no rigid hull parts that extend past the air cushion. It therefore can operate across the beach. The SES has rigid side hulls that enclose the air cushion, permitting water propulsion but allowing it to only go to the shore when conducting amphibious operations. Design concepts for a 6000-plus-ton cargo SES's that Rohr and [[Ingalls Shipbuilding]] proposed relied on the idea of the ship loading and unloading from beach, lighter, [[causeway]] or conventional dock facilities.

On 10 November 1972 contracts were let to four firms to conduct 2200-ton prototype preliminary design; these designs were to be completed in August 1973. The [[Prime contractor (US Government)|prime contractor]]s were [[Bell Aircraft|Bell]], [[Aerojet]], [[Litton Industries|Litton]], and [[Lockheed Shipbuilding and Construction Company|Lockheed]].<ref>[https://babel.hathitrust.org/cgi/pt?id=uc1.b4292120;view=1up;seq=1059 Surface Effect Ship (SES)] - Department of Defense appropriations for 1974, V.5</ref>
[[File:Seaspeed hovercraft.jpg|Hovermarine HM2|thumb|right]]

==== Aircraft carrier surface effect ship ====
Proposed concepts for an aircraft carrier surface effect ship were considered.<ref>https://www.history.navy.mil/our-collections/photography/numerical-list-of-images/nhhc-series/nh-series/USN-1165000/USN-1165638.html</ref><ref>https://arc.aiaa.org/doi/10.2514/3.48209</ref>

===Hovermarine SES Ferries===
The UK based company Hovermarine developed the HM.2 SES ferry at their factory in [[Woolston, Southampton]] in the 1960s.<ref>{{cite book |title=A Dictionary of Aviation |first=David W. |last=Wragg |isbn=9780850451634 |edition=first |publisher=Osprey |year=1973 |page=157}}</ref> The first HM-2 craft was operated by [[Seaspeed]] in 1968 between [[Ryde Pier]] and [[Portsmouth Harbour]]. The early HM2 suffered from mechanical problems and during a financial crisis in 1969, Hovermarine went into voluntary liquidation and the major assets were acquired by a new company, Hovermarine Transport Ltd, this was subsequently taken over by the American company, Transportation Technology Inc. Production of HM.2s for North and Central America was undertaken by Hovermarine's factory at [[Titusville, Florida]]. A brief trial of 2 HM.2 took place in [[Toronto]] from July to late fall 1974 to [[Niagara-on-the-Lake]] to [[Youngstown, New York]]. The service managed by [[Can-Am Hover Express]] used two craft, Toryoung I and Toryoung II, but an accident with the latter craft led to the demise of the service.<ref>{{Cite web|url=http://www.maritimehistoryofthegreatlakes.ca/documents/scanner/07/06/default.asp?ID=c003|title = Scanner, v. 7, n. 6 (March 1975) : Marine News}}</ref>

Over 110 HM.2's were manufactured in the United Kingdom and United States.
=== Japan ===
In Japan, two type of SES were built: {{ill|Kibou|ja|希望 (高速フェリー)}} and {{ill|Super Liner Ogasawara|ja|テクノスーパーライナー#小笠原TSL}}.

Kibou was operated as a car ferry between Shimizu port and Shimoda port in Shizuoka prefecture. It was 2780-ton, 74m long with 2×MFT8(JT8D) engines. Vessel was decommissioned in 2005.
Superliner Ogasawara was planned to operate between Tokyo port and Ogasawara island in Tokyo prefecture, but it was cancelled because of high jet fuel cost in 2005. It stayed in Ishinomaki Port as a hotel ship for victims of the Tunami disaster in 2011. It was later scrapped in 2018. Vessel was 14500-ton, 140m long powered by 2×LM2500 engines

==Operational use==
=== Russia ===
<!-- The Russian Navy built a 600-ton combat SES (DERGATCH). Its status is unknown. Ed. note: I believe this references the Bora class. Please correct as required. -->
The [[Soviet Navy]] built two 1050-ton [[Bora-class corvette|''Bora''-class surface effect corvettes]] in the late 1980s and early 1990s. The ships were passed on to the [[Russian Navy]] and remain in active service with the [[Black Sea Fleet]].

=== Norway ===
[[Umoe Mandal]] built 9 [[Alta class minesweeper|Alta and Oksøy class]] surface effect vessels for mine warfare for the [[Royal Norwegian Navy]].

The Norwegian Navy also operates six [[Skjold class patrol boat|Skjold class]] surface effect patrol boats. These ships are the fastest warships in the world with service speeds of {{convert|60|kn|km/h}}. The prototype ([[Wiktionary:KNM|KNM]] Skjold) was leased and tested for one year by the US Navy.

=== Sweden ===
[[HSwMS Smyge]], which acted as a small-scale pre-prototype testbed for the [[Visby-class corvette]] is now used as a training platform for [[Swedish Amphibious Corps]] [[Clearance diver]]s.

=== North Korea ===
The [[Korean People's Army Naval Force]] operated 6 [[Nongo-class warship]].

== See also ==
* [[Air cavity system]] is a related technology.
* [[Ground-effect vehicle]]
* [[Aerodynamically alleviated marine vehicle]]
* [[List of amphibious warfare ships]]

==References==
{{Reflist}}

==External links==
*[https://www.youtube.com/watch?v=k_w_GasHYlk US Navy's SES-100B Surface Effect Ship]

{{DEFAULTSORT:Surface Effect Ship}}
[[Category:Air-cushion vehicles]]
[[Category:Ship types]]
[[ja:地面効果翼機]]