Defense Technology International - July 2007 - (Page 22)

DISPATCHES GLOBAL PRECISION ARRAY New ASW system lets small ships target stealth subs JORIS JANSSEN LOK•BREST, FRANCE sonar,” says Philippe Portalier, strategy director for Thales Underwater Systems in Brest. Captas Nano (also known as UMS 4320) has no towed body. It uses a single transmit-and-receive array equipped with about 30 diabolo-shaped staves in the transmit section. These acoustic transducers, operating at 1-2 KHz., are derived from an active sonobuoy technology developed by Thales Australia. They have no moving parts; rather, they feature an active ceramic material that vibrates from application of electric power. The resulting deformation of the ceramic sends a high amount of acoustic power into the water, according to Portalier. Each diaboloshaped stave has a speciﬁc phase, which in the sector mode can be combined to create directional beams or omnidirectional pings. Like other Captas Captas Nano active/passive towed-array systems, the receiving sonar from Thales has no towed body. It array makes use of uses a single transmit-and-receive array with Thales’s triple hydroautomatic deployment and recovery. phone concept, which allows for single-ping The main product line for anti-sub- omnidirectional surveillance and instant marine warfare is the Captas family of left-right ambiguity resolution. “The last towed-array sonars that use powerful is important when detecting torpedoes low-frequency active transmissions and an immediate response is required,” and highly sensitive receive arrays. says Portalier. (Captas stands for combined active/ Captas Nano also requires just a sinpassive towed-array sonar.) The com- gle winch, and features an automatic pany’s newest product, Captas Nano, launch and recovery capability. Thales continues to offer new systems permits navies to equip ships as small as 500 tons with an active, towed low- and upgrades for larger ships. The French frequency sonar array. Some previous navy’s Slasm system, developed by Thales Captas sonar arrays, by contrast, are so in the early 1990s, was the ﬁrst low-frelarge they can only be used on ships of quency, tactical, variable-depth sonar in service worldwide, says Portalier. at least 3,000 tons. Thales has sold three Captas 20 sys“Although Captas Nano will not have the same power as the larger Captas tems to Saudi Arabia, followed by the systems, it will still be better than what current Captas Mk. 2–UMS 4229, also can be achieved with a hull-mounted known as “Captas Light,” that uses a hales Underwater Systems is making major investments in towed-array sonar technology for use by surface ships in anti-submarine warfare. Much of its work is directed at an emerging threat: quiet submarines that lurk in littoral waters. Recent advances in submarine construction are yielding a new generation of nonnuclear boats that can run submerged for weeks, operate quietly in as little as 20 meters (65 ft.) of water and yield low radar proﬁles when surfaced (see p. 24). THALES CONCEPT T towed body with two free-ﬂooded-ring transducers and a passive receive array attached to it. UMS 4229 has been procured by Norway for ﬁve Nansen-class frigates built by Navantia of Spain. A version called UMS 4249—“Captas Heavy”—features a towed body with four free-ﬂooded-ring transducers and a receive array that streams separately from the active towed body. One drawback to the UMS 4229— and to the Captas 20 systems, which are similar except for a shorter receive array—is that the receive array needs to be manually attached to the towed body on the quarterdeck when deploying and decoupled during recovery. The UMS 4249 version is the basis for the Royal Navy’s Sonar 2087 lowfrequency towed-array system in use by eight Type 23 frigates. It has also been speciﬁed for 12 Fremm multipurpose frigates in France and Italy, though in a modified version with off-the-shelf Pentium processing boards and a Linux operating system. The Sonar 2087 system is deployed close to the waterline of the Type 23 frigates. To retrofit the systems, the aft ends of the ships are being reconﬁgured. So far, three 2087s are at sea, a fourth ship is being reﬁtted, and the ﬁfth system has completed testing. Sonar 2087 has an auto-deployment system, resulting in reduced manpower requirements and enhanced safety. The feature functions in Sea State 4 conditions. When the towed body and receive array are deployed, the former typically goes deep behind the ship, while the latter stays shallow so the vessel can be maneuvered without the arrays colliding or becoming entangled. The towed array requires about 30 min. to fully deploy. The Sonar 2087 version of UMS 4249 differs in several ways from the Slasm system. Its active towed body weighs 2.5 tons, while Slasm’s body weighs 10 tons. Slasm is full of water during recovery; the Captas towed body contains only about 300 liters (79 gal.) of water. The 2087, however, has a major footprint on board, and is used on ships that displace 3,000 tons or more. Sonar 2087 also requires a handling system for the towed body and another one for the receive array. The lighter Mk. 2 Captas, as ordered by Norway, has only one handling system and can be integrated on ships as small as 1,5002,000 tons. I Read Janssen Lok’s posts on DTI’s weblog, Ares, updated daily: aresblog.net www.aviationweek.com/dti 22 DEFENSE TECHNOLOGY INTERNATIONAL JULY/AUGUST 2007 http://aresblog.net http://www.aviationweek.com/dti

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Defense Technology International - July 2007

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