FFL Trimaran Light Frigate

China’s People’s 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 Dhabi’s IBEX expedition, and showcased many possible features for the vessel.

You Yue, deputy director for China Shipbuilding Trading Company’s 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.

From the current published model and display panel data, this is not a conceptual design, but has completed the complete ship design and proposed relevant core data. According to the information on the exhibition board, the ship has a total length of 142 meters, 100 crew members and a displacement of 2,450 tons, which is slightly smaller than the tonnage of the main frigates of the Chinese Navy. Its maximum speed can reach 30 to 35 knots, and this speed index greatly exceeds the 056 and 054A series frigates currently in service in the Chinese Navy.

Under the premise of ensuring that the length and width of a single hull are relatively large, the total width of the hull of the new three-body frigate is relatively large. The full width of 32.6 meters exceeds that of the same class frigate, which makes it have a large double hangar and apron, and can use medium-sized or even 13-ton large-scale ship-borne helicopters. At present, the main naval destroyers of the Chinese Navy (the 052C/D destroyer and the 054A frigate) can usually only carry one Russian-made card type-28 medium-sized anti-submarine helicopter or a 4-ton-class domestic straight-9 series anti-submarine helicopter.

In addition to the advantages of the three-hull ship, the stealth performance of the new foreign trade three-body frigate is also very good. Its ship adopts a high-speed wave-piercing type, and the freeboard has obvious fold lines extending to the middle of the ship. The transition joints on the surface of the hull structure are mostly obtuse or rounded, and most of the shipborne equipment is placed inside the hull. The entire front of the hull is up to the bridge. Except for one stealth naval gun and the vertical launch system of the ship-to-air missile, there is no protruding structure, which is extremely simple and clean.

The middle part of the hull is an inward-looking stealth shipyard, and the top of the ship's building is a comprehensive stealth mast that integrates most radar, communication antennas and sensor devices. The search radar of the new three-body frigate has more improvements than the 054A missile frigate. The 382-type frequency sweep three-coordinate radar is no longer used, and the expected "small shield" appears - a new generation of single-sided phased arrays. Radar, this is also the standard configuration of a new generation of Western advanced destroyers. In addition, the ship's ship's height is significantly lower than the current mainstream frigates, which will significantly reduce its forward radar reflection projection area, which is extremely beneficial for reducing the RCS signal.

In terms of weaponry, the three-body frigate is equipped with a H/PJ-26 single-tube 76mm stealth main gun with a range of 15.5 kilometers. In addition, there are 2 H/PJ-12 7 tubes and 30 mm near-proof guns, which can play 4,200 rounds of bullets per minute. There are also two 726-4 multi-function interference devices above the hangar. It is worth mentioning that this type of frigate is also equipped with a 32-unit slinging device. There are two sets of AJK-16 anti-aircraft missile illuminating radars in front of the main stern. This proves that the slinging device of this type of equipment is AJK. The -16 will be equipped with the Haihongqi-16 medium-range air defense missile.

Haihongqi-16 medium-range air defense missile China's third-generation medium-range air defense missile, equipped with large and medium-sized destroyers, used for medium and short-range regional air defense and self-defense anti-missile operations, mainly intercepting anti-ship missiles and aircraft-type targets, with Good load adaptability, vertical thermal emission technology, and comprehensive ability to quickly intercept multiple targets. The maximum flight speed is Mach 2.58, the effective range is 1.5 to 40 kilometers, and the effective shooting height is 10 to 25,000 meters. This is the first time that China has indicated that it will export this class of carrier-based air defense missiles.

The middle recess of the superstructure is designed with two four-mounted anti-ship missile launchers. It is inferred from the appearance of the launcher that it should be the domestic "Eagle Strike"-83 series missile. According to the latest information, the extended range of the "Eagle-83" missile has exceeded 200 kilometers. In terms of anti-submarine capability, the ship is equipped with a new type of active/passive sonar system, and there are three 324 mm light torpedo tubes on both sides of the hull. As mentioned earlier, this type of frigate has a dual hangar that can carry two medium-sized anti-submarine helicopters. The number of helicopter hoards and the size of the apron will directly determine the ship's anti-submarine warfare capability.

In terms of powertrain, the exhibition materials show that the new three-body frigate uses the "diesel-driven ship propulsion system", which indicates that it may adopt an integrated electric propulsion system (IPS). At present, the domestic electric propulsion system has been used for sea surveillance vessels and semi-submersible vessels. This is also the first time to be adopted on export-type ships. This is another major breakthrough for domestic surface ships. It can be clearly seen from the model that the ship uses a water jet propulsion system instead of a general propeller propulsion. In fact, on the previous 917 three-body rescue boat, the water jet propulsion system has been successfully used.

One of the characteristics of the water jet propulsion system is high speed performance, small radius of gyration, good maneuverability, simple structure and low vibration, which can effectively reduce noise. The combination of the integrated electric propulsion system and the water jet propulsion system enables the domestically produced new generation of high-performance frigates to have better high-speed performance and maneuverability. The exhibition data shows that the cruising speed of the new three-body frigate is 25 knots, while the cruise speed of the general ship-type destroyer is mostly around 15-18 knots. The significance of the maximum speed is generally the instantaneous speed of the ship's speed, and the significance of this cruising speed data is durability, which means that the new three-body frigate can run longer and farther at high speeds, up to thousands of nautical miles.

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).