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FFL Trimaran Light Frigate

Chinas Peoples Liberation Army Navy (PLAN) is reportedly designing a trimaran ship that could serve as both an export vessel and a naval frigate. The PLAN will probably not begin construction on the first trimaran frigate before 2018, as the design has not yet been finalized. The design was modeled by the China Shipbuilding Trading Corporation (CSSC) in February 2017 at Abu Dhabis IBEX expedition, and showcased many possible features for the vessel.

You Yue, deputy director for China Shipbuilding Trading Companys business development in Western Asia and Africa, said, "We are in the development and design phase of the project The plan form is fixed but many details remain," according to Defense News. You noted, however, that it is not necessarily an accurate representation of a ship currently being built.

The specifications provided by CSSC for the trimaran vessel, according to information displayed alongside the model, state that it displaces 2,450 tonnes, has a length of 142 m [466-feet], a width of 32.6 m [105 feet], a cruising speed of 25 kt, and an endurance of 30 days. A CSSC official added that its top speed is between 30-35 kt and that it has a crew of more than 100.

A marine electric propulsion system is to be given to the power plant, with a 5,000 nautical-mile range at 16 knots, and 30-day endurance at 25 knots. The China shipbuilding spokesman explained that these numbers could differ in a production ship, with speeds likely passing 30 knots, and that the company was considering an all-MTU diesel-propulsion plant, driving three waterjets.

Although lighter than China's Type 054A frigate, the trimaran carries a similar armament. The military variant of the trimaran showcased a vertical launch system for surface-to-air missiles ahead of the superstructure as well as chaff launchers behind the gun. Models also offered included a 76 mm to 100 mm gun, surface-to-surface missiles in canister launchers amidships, close-in weapon systems, and other weaponry typically found in smaller warships. Above decks featured a double hangar, along with side doors designed to launch small boats, though below the flight deck there are no stern doors and no mission bay.

Though shorter, the 127 meter USS Independence trimaran Littorial Combat Ship is a high-speed platform, with a top speed estimated at over 40 knots, faster than the Chinese trimaran frigate's 30-35-knot top speed. The 2,450 ton Chinese trimaran is more heavily armed for conventional warfare. The 2,800 ton American trimaran only mounts a 57mm cannon with provisions for anti-ship missiles, while the Chinese ship has a 76mm cannon, anti-ship missiles, and vertical-launching system cells for carrying anti-ship, land attack cruise and anti-air missiles.

Trimarans are vessels with one long, thin hull and two side hulls (amahs) to provide stability and prevent the vessel from capsizing. Because the side hulls are small in comparison to the main hull, the main propulsion machinery is usually fitted into the main hull. Trimarans typically comprise a main hull and two side floats or pontoons positioned one on each side of, and a distance from, the main hull to improve the stability of the vessel.

The radar signature will be reduced by the shape of the superstructure and hull as well. Multihull ships are widely used for sea transportation, and those with four hulls are known as quadramarans. In general, multihull vessels traveling at high speeds have better hydrodynamic efficiency than monohull ships. As a new type of hull form, trimaran has remarkable excellent performances and has drawn more and more attention. Trimaran has a series of outstanding merits,its excellent performance of speediness,sea-keeping and stability have made it a wide application.

Sea-going trimarans have been manufactured as vehicular ferries, passenger ferries and as warships. In most of these designs, the space above the main propulsion machinery has been used as a cargo space. In the case of vehicular ferries, the space above the engine room is used for the transport of cars and other wheeled vehicles, including trucks and coaches. Due to the required hull configuration, trimarans built to date only have stern loading/unloading arrangements, necessitating that vehicles either turn around on-board, or reverse from the vessel. It is clearly advantageous to make the vehicle space as open as possible and without obstruction, so that trucks, including articulated vehicles, can safely manoeuvre on and off the vessel.

The outrigging side hulls are usually smaller in length and cross section than the main hull and have considerably less draft. The amahs are designed to provide buoyant support for a trimaran, especially at slow speeds and also to provide adequate stability. For a high speed vessel it is required that the amahs should be as small as possible to minimise drag and thus naval architects generally design trimarans with the amahs of minimal length and width consistent with the need for adequate stability.

The width of the amahs in way of the water must also be minimized in order to reduce the drag and reduce the generation of waves which may impact upon the main (centre) hull of the trimaran, thus causing additional drag. Typically the width of the amah in the water for a vessel having a length of about 120 metres may be as small as 700 millimeters at the top, tapering down to zero width at the bottom. Access for construction and maintenance is further substantially limited because of the internal stiffening structure.

Stability is central to the proper design of all vessels. The obvious need for stability influences all decisions regarding shape, location and weight of the many components required to produce a practical and safe watercraft. The two primary aspects of stability that need to be addressed when designing a vessel are fore-and-aft stability (pitch) and side-to-side stability (roll). Pitch stability does not pose as thorny a design problem as roll stability, since each of the buoyant parts of vessels have greater length than width.

There are three common hull forms in use today: monohull, catamaran and trimaran. The resulting moments of each design tend to keep the vessels in an upright position. All hull designs use a combination of factors to ensure roll stability in most conditions. While trimarans have many advantages, there is one significant drawback associated with conventional trimarans. A conventional trimaran reaches its greatest stability at 20-35 inclination, and at larger inclinations the stability steadily decreases down to zero at about 80 inclination. Thus, trimarans can capsize due to the impact of wind or waves, and are not self-righting, so that once capsized they remain upside down.

Multihull vessels obtain their stability by distributing their buoyancy between two or three spaced-apart hulls. This eliminates the need for ballast. As a result of the lack of ballast, the multihull vessel has a general tendency to float even when flooded. The typically lightweight construction of this type of vessel also aids in keeping the craft afloat.

The trimaran hull gives the ship the ability to have a much greater width than common monohull designs. Some problems stem from the fact that the width of most multi-hull sailboats is quite large compared to that of single hull boats. Although this increased width improves their stability in water, it makes them difficult to maneuver. In terms of performance, based on a strict speed-to-length ratio, multihulls require less power than monohulls of similar size to achieve equal speeds. Conversely, with equal power input, multihulls can achieve higher speeds than monohulls. This relationship is due to the reduced form resistance of the multihull's lighter, narrow hulls (in contrast to the wider, heavier form of a monohull of equal capacity and/or length).

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