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Nongo Surface Effect Ship (SES)

The North Korean Surface Effect Ship (SES) is known as the Nongo class by the US Department of Defense. One side of Nampo Naval Base is used to build, modify, and refit ships. This side of the base is also the site of the Naval commands (NAVCOM) headquarters building. Various naval contruction halls are present, including those used for newly constructed North Korean Surface Effect Ship (SES). The import by the DPRK of the Kh-35E anti-shipping cruise missiles was first disclosed in early 2012 in a North Korean video of an SES showing racks used to mount four Kh-35 canisters.

This Fast Attack Craft appears to have significant radar signature reduction characteristics. Torpedo boats with these features were exported to Iran in about 2002 (Tir and Peykaap classes). The armament on this craft appears to include a 57mm [56mm?] medium caliber main gun mounted on the foredeck, and a smaller 30mm AAA turret on the aft deck.

The hull is very wide, suggesting that it is a surface effect ship (SES) similar in principle to the infamous Soviet Bora class, or the more modern and stealthy Norwegian Skjold class. News reports suggest a 90km (50kts) speed. North Korea has a large number of hovercraft which it has been producing since 1987, but in this case the absence of visible external propulsion points away from pure hovercraft and towards SES.

In addition to the Nongo type there are at least two similar boats on the West coast clearly visible on Google Earth satellite imagery. The boats do not match any known type. The hull proportions generally match the Nongo type but are possibly slightly shorter (35m v 38m) and clearly non-stealthy. Although the two West coast boats are very similar to each other they have significant differences suggesting that they are two separate but closely related types.

The "Type A SES" is probably a reasonably capable missile boat of relatively recent construction. The layout follows the standard Russian pattern, with the missile tubes beside the bridge firing forward, and a long superstructure extending rearwards almost to the stern. There appears to be a medium caliber gun on the aft deck but something smaller, probably a 30mm CIWS, to the bow. The arrangement with the main gun at the rear is again more typical of Russian missile boat designs than Western ones.

The "Type B SES" differs from SES-A in having a more squared bow, the medium caliber gun at the front not back, and a more separated superstructure. The anti-ship missile mountings are clearly visible.

One of the primary objectives in boat design is to reduce the amount of drag caused by the interface of the hull with the water surface. Early planing hulls were designed so that forward motion of the hull raised the vessel to cause it to ride on a smaller portion of its hull surface resulting in reduced hull-to-water friction. The design of hydrofoil vessels further reduced hull contact with the water by attaching foils to the hulls upon which the boats ride at high speed. Some marine vessels interpose a film of air between the vessel's hull and the water to reduce the hull-to-water friction.

Two primary types of high-speed advanced marine vehicles are the surface effect ship (SES) (or surface effect vehicle (SEV)) and the fully skirted hovercraft. Both are considered air-cushioned vehicles (ACV) in that each rides on a pressurized cushion of air. Surface effect ships were an improvement over the air film hulls as the hulls of surface effect ships are raised out of the water by a pressurized air cushion that is partially captured within the hull of the vessel.

The prior art of air cushion vessel hull designs contained the air cushion with flexible seals, which are a rubberized curtain, either all around the vessel as in the case of the hovercraft air cushioned vessels, or across the front and the back of the vessel with thin parallel side hulls that provide a side seal for the air cushion as in the case of surface effect ships. The flexible seals reduce the amount of air lost from the air cushion but create a rough ride, "a cobble stone ride," even in smooth water. As the surface of the water becomes rougher the flexible seals can be separated from each other, causing further deterioration in ride quality. Also, in rough water the flexible seals frequently fail to maintain the air cushion, causing the craft's hull to drop lower into the water until the seal is regained and the air cushion is reestablished.

The large and medium operative surface effect ships are equipped with a heavy machinery to transfer the power of the engines to the lift fans and the propellers, to provide with required flow volume, cushion pressure and thrust. The machinery of these ships is heavy, mechanically complicated and consists of many multilink driving shafts, clutches and reduction gears. Typical of such surface effect ships are LCAC, built by Textron Marine Systems, USA, and SR.N6, SR.N4 built by British Hovercraft Corp., Ltd., United Kingdon. In the SR.N4, for instance, driving shafts from the engines to lift fans are 18.3 meters long.

The air cushion of the SES or SEV is contained on the sides by relatively thin, rigid, lateral walls contacting and protruding into the water, and at the front and rear by flexible or semi-flexible seals or skirts. Though the hovercraft skirt theoretically can have a lower drag due to the air gap which would give no interaction with the surface, in reality considerable drag can be experienced in rougher water due to wave interaction with the skirt's fingers.

The SES will have considerably lower hydrodynamic drag in rougher water due to the thinness and rigidity of the side-walls as opposed to the unwieldy side portion of the skirt of the hovercraft. A further advantage of the SES is that since its side-walls protrude below the water surface there is practically no air loss out the sides. The reduced drag of the SES reduces the thrust required to achieve a given speed, and the reduced air loss reduces the power required for the lift fans. In addition, water-jet or other water propulsion means may be employed with the SES which are generally more efficient than air-propellers on hovercraft. Also, the operational costs of the side-walls on the SES are much lower when compared to the side portions of the skirt of the hovercraft.

NongoSES ASES B
Length 3540m35m35m
Beam12m12m
Displacement approx 200tapprox 200t
Armament
  • 1 x main gun (57mm?)
  • 30mm AAA
  • 2-8 anti-ship missiles (depending on type)
  • 2 AAA (30mm?)
  • 1 medium caliber dual purpose gun (85mm?)
  • 2-8 anti-ship missiles (depending on type)
  • 1 x medium caliber gun (85mm?)
  • 1 x AAA (30mm?)
  • Speed48kts




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