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AOS Hibiki Class

The AOS Hibiki is a new class built for the purpose of collecting sound print data. Submarines have been upgraded so they are more quiet, can dive deeper, and make different sounds. The construction of this new class was planned to respond so such changes. Hibiki, at its completion in January 1991, sailed to the United States for the installation of SURTASS.

Japan envisaged the shipbuilding project in 1987 at the strong urging of the United States. After the Cold War, a new project to build more (ocean surveillance) ships was shelved. The project came back to life in the Defense Ministry’s National Defense Program Guidelines issued in late 2013. The guidelines are compiled every 10 years or so to carve out Japan’s mid- and long-term defense policy. The purpose of reviving the old program was to gather intelligence on the Chinese Navy’s submarines.

In May 2018 the Ministry of Defense (MoD) in Tokyo announced that a third 67 m-long ship was being built for JPY18.3 billion (USD164 million) under a contract awarded to Mitsui E&S. The Aki (with pennant number AOS 5203), it is the first new Hibiki-class ship built in about 30 years. The vessel entered the water on 15 January in a ceremony held at the company's facilities in the Japanese city of Tamano, Okayama Prefecture. Mitsui E & S Shipbuilding Co., Ltd. (President: Tetsuro Koga) performed the naming ceremony 04 February 2020 of the 2,900-ton acoustic measuring ship for the Ministry of Defense (No. 2000 ship) at the Tamano Ship Factory with the presence of the Ministry of Self Defense. The Vessel was the third of 2,900 ton-type acoustic measurement ships planned in 2017 and was named "Aki". Outfitting work was performed at the quay and was delivered in March 2021. The ship, which has a full-load displacement of 3,048 tonnes, was commissioned on 04 March 2021. Japan’s first ocean surveillance ship in nearly 30 years, it features a more advanced Surveillance Towed Array Sensor System (SURTASS) than that fitted onto the first two ships of the class.

Of the 22.6 billion yen in costs to build the Aki, 2.3 billion yen was used to buy the Surveillance Towed Array Sensor System (SURTASS) from the United States through Washington’s Foreign Military Sales program, which manages U.S. sales of defense equipment to foreign governments. SURTASS is part of an undersea surveillance system that tracks submarine movements. Although the equipment is essential to the new surveillance ship, it is like a black box for the MSDF because Japan’s naval arm has no access to the heart of the undersea surveillance technology.

The Hibiki-class of Ocean Surveillance Ships mission is to gather undersea acoustic data emitted by foreign submarines. Therefore, Aki is equipped with a surveillance towed-array sensor system (SURTASS), which is a very long range active / passive sonar that can be deployed into the sea to collect various acoustic data. SURTASS is also installed on Ocean Surveillance Ships operated by the United States Navy’s Military Sealift Command (USNS Victorious, Able, Effective, Loyal, Impeccable).

"Acoustic measurement ship" is the Japanese term for this type of ship, but their equivalents in the US are called ocean surveillance ships. The role of the Hibiki-class is to detect, track, and monitor submarines in Japanese or near-Japanese waters, as well as to gather acoustic data at sea (particularly that of submarines) for analysis. They were designed in the late 1980s as a response to the increasing stealthiness of Soviet sub designs, ironically becoming a major concern as the Japanese firm Toshiba had sold technology and machinery that allowed them to build quieter screws, which came to light in the Toshiba-Kongsberg Scandal. However, they are not in themselves anti-submarine warfare platforms, as they are completely unarmed. They act only as the JMSDF's ears, and are not combatants.

They are very similar in design and role to a number of other ships - the American Victorious-class and the USNS Impeccable, and the Chinese Type 639. The one major difference between these and the Japanese ships is the huge helidecks present on the Hibiki-class, although they have no hangar. The Hibiki- and Victorious-class ships were first commissioned in the same year, 1991, and may be of related design, although there is no clear indication of how much one design influenced the other. They do however both use the Surveillance Towed Array Sensor System (SURTASS) as their main tool.

Another SWATH design operated by Japan is the Kaiyo ("Ocean"), an oceanographic research vessel used by the Japan Agency for Marine-Earth Science and Technology (JAMSTEC), essentially Japanese NOAA. Because it is made by the same manufacturer at about the same time, it may be a related design, even though it's a civilian ship.

The Hibiki-class are named after "nadas". A "nada" in Japanese is an area of sea that has particularly rough waters and strong currents. There does not seem to be a close equivalent English word. AOS-5201 Hibiki: "Hibiki" is a word that means echo, reverberation, or more generally as a verb that refers to the travelling of sound. The Hibiki Nada is the stretch of sea northwest from the Kanmon Straits between Honshu and Kyushu. AOS-5202 Harima: The Harima Nada is in the middle of the Seto Inland Sea, between Honshu and Shikoku. Harima is the name of an old province that was on the Honshu coast north of the Nada.

The Hibiki-class hull structure is called Small Waterplane Area Twin Hull (SWATH). The SWATH design is like a catamaran, but with very large submarine-shaped twin hulls beneath the waterline. This places the majority of the ship's displacement completely under the wave action, increasing stability at the cost of speed.

This structure improves wave resistance by reducing the volume of the ship near the sea surface and increases the stability during navigation. The Hibiki-class is required to operate at a low speed during surveillance activities using the SURTASS, and this special structure allows it to remain stable while underway even in bad weather and sea states.

Advances in naval architecture have led to the development of a semisubmerged ship having a plurality of hulls completely disposed beneath the surface of the water in which the ship is deployed. Such vessels enjoy a dynamic pitch stability and a maneuverability superior to monohull vessels of conventional design. Because of its superior stability and maneuverability at all speeds, the SWATH ship offers an excellent platform from which various physical measurements of the ocean environment can be carried out. The usual means for carrying out real-time marine measurements is to trail a sensor package behind the moving marine vessel by means of a negatively buoyant towline attached between the vessel and the package. In conventional such an apparatus is normally deployed by paying out the package and line over the stern of the ship and towing them behind as the vessel moves through the water.

In the case of the SWATH ship, the stern deployment technique can interfere with efficient vessel operation and pose a danger of equipment damage. The combined weight of the towed array, storage reel, and related mechanical equipment is such that if the equipment were to be located at the stern of the SWATH, rather than amidships, the vessel would become imbalanced to the detriment of its stability and maneuverability. Also, because of the horizontal stabilization member connecting the submerged hulls at the stern of the ship, and because of the propellers which protrude from the hulls, a sensor package cannot be deployed from a position amidships while the ship is moving in a forward direction without running the risk of damage to the package, towline, or ship. Hence, a novel method of instrument deployment from a SWATH ship is required which will ensure the correct launching of the package without danger of damage.

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Page last modified: 06-06-2021 18:22:00 ZULU