Type 639 underwater sound measurement ship
There is a small water surface double-body survey ship built for the Chinese Navy. The name of the ship is “Northern 991”, which is a 639 type double-body underwater acoustic survey survey ship. As its name suggests, its role is to detect and collect underwater acoustic information features. The displacement is 1,500 tons, and in order to reduce the noise, the first full-electric propulsion is adopted. In terms of appearance, it is more like a civilian ship, far from the might of new measuring vessels. This is also a small water surface two-body measuring ship equipped by the Chinese Navy. It is similar to the "Northern 991" structure. This is probably an upgraded version, and the function may be stronger.
The vessel called SWATH which means Small Waterplane Area Twin Hulls is becoming popular. SWATH consists of two lower hulls under water, an upper hull above water and struts connecting these. SWATH navigates in a semisubmerged state and this vessel receives the buoyancy force derived from the displacement of the submerged hulls. Thus the scale up to a large vessel can be easily done and the cargo can be carried on the upper hull without limitation. However, as long as self-stabilizing ability is needed for the SWATH, SWATH cannot avoid oscillation. And also it causes big trouble that SWATH has the submerged hulls in the shallow draft state.
Modern Naval ships are typically designed to perform multiple types of missions, and are, therefore, referred to as "multi-mission" ships. For example, suppose a ship is designed for anti-submarine warfare, littoral warfare, and anti-mine warfare. Such a ship may include a deck that has a respective command/control station for each type of mission, i.e., a station for anti-submarine warfare, a station for littoral warfare, and a station for anti-mine warfare. The ship may also have a hull that, although not ideal for any particular type of mission, is at least compatible with all of the mission types for which the ship is designed for.
One problem with such a multi-mission-type ship is that it is often larger than it needs to be for a single type of mission. For example, if a deck of the ship has a respective command/control station for each type of mission, then the deck, and most likely the ship, is bigger than it would be if it included only a single station for a single type of mission. Multi-mission ships are, therefore, high-value capital assets, are typically designed to carry a large crew to support the various missions, and are generally operated only in regions where high degree of protection is supplied by other friendly ships. Another problem is that such a multi-mission-type ship is typically inefficient. For example, if the ship is designed to perform three types of mission and includes a respective command/control station for each mission type, then two of the three stations are typically unused when the ship is on a mission.
Underwater acoustic surveillance systems and methods that now carry out the tasks detecting, locating, identifying, and tracking submerged objects, particularly submarines, through the transmission and reception are usually divided into two categories designated as "active" and "passive", although some mixed systems are also employed. Active underwater sonar surveillance systems are usually monostatic, i.e., the same platform is used for transmitting and intercepting these signals. A disadvantage to using an active system is that a targeted object may be able to trace the signal back to the transmitter platform. Should the target be hostile, such as an enemy submarine, it may be able to use this information to interdict the transmitter platform or to take evasive action. Submarines have also adopted, as stealth countermeasures, hull designs and construction materials that absorb or diffuse sonar signals making these reflected echoes difficult to detect and analyze.
In passive acoustic underwater surveillance, listening platforms employ hydrophones to monitor the underwater sounds present in the ocean environment. Recognition of characteristic sounds, called "acoustic signatures", of various vessels lead to their detection and identification. Submarines, however, have become quieter and are developing increasingly more effective stealth techniques enabling them to more successfully evade detection by passive systems. Also, a submerged object which is emitting no sound, such as a stationary submarine, would be undetectable to a purely passive system.
The North Transfer 991 (Dongyuan 02) is a 639-type dual-body underwater acoustic survey survey vessel. It is the first 1,500-ton small waterplane catamaran with independent intellectual property rights in China. It was initiated by CSIC. The established CSSC Dongyuan Technology Development Co., Ltd. is responsible for the overall organization management and coordination of R&D, design and construction. It was jointly designed by 710 and 702 Institutes, built by Wuchang Shipyard, and its electric propulsion system is integrated by 712 Institute. The main marine equipment and special test equipment are manufactured by Wuhan Marine Machinery Co., Ltd., Henan Diesel Engine Group Co., Ltd., Shanxi Minxi Heavy Industry Co., Ltd., Chongqing Huayu Electric Instrument Factory, Beijing Great Wall Radio Factory, etc. All grouped products developed by CSIC.
The ship has a wide deck area and excellent seakeeping and maneuverability. In the design, it mainly solves the line type optimization of the shallow draft small water line catamaran, the structural design of the large opening double body hull structure, the integration of the integrated electric propulsion system, the development of the high precision long stroke special test device, and the whole ship floating state adjustment aid. Key technologies such as decision systems. In the construction process, the full three-dimensional production design ensures the correct design, weight center of gravity control and manufacturing precision; 11 new processes such as typical submerged welding process, large-scale well welding process, and full ship weight control implementation rules have been prepared. The document solves key construction techniques such as thin-plate welding, weight control, and vibration noise. After the sea navigation test, the ship's performance and various technical indicators have fully met the design requirements.
From the top view, the central hull has a "square well", which should be the working area for the suspension and recycling of underwater sound equipment. Note that there is a small crane there, and there seems to be a towing winch. Such a design differs from that of the US and Japan in the rear of the hull. The layout of the “Northern 991” may require anchoring during the measurement work, so the ship has three anchors arranged in front and rear.
Type 639/639A series ships in PLAN service are designated by a combination of two Chinese characters followed by three-digit number. The second Chinese character is Shui, meaning research, or Ce, meaning survey, because these ships are classified either as oceanographic or hydrographic research. The first Chinese character denotes which fleet the ship is service with, with East (Dong) for East Sea Fleet, North (Bei) for North Sea Fleet, and South (Nan) for South Sea Fleet.
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