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LIFTING BODY TECHNOLOGY STARTS LARGE SCALE TRIAL
(From Speed At Sea, August 2003) by David Foxwell
Lifting body technology under development in Hawaii is designed to make a wide range of conventional hullforms more stable at low speeds and more efficient at higher speeds, as well as giving them extended range. These hullforms include monohulls, catamarans, trimarans, small-waterplane-area ships as well as decp-V, partial hydrofoil and hydrofoil hullforms. The work is being carried out by Navatek, whose primary customer is the US Navy’s Office of Naval Research (ONR).
Navatek is based in Honolulu and is a wholly-owncd subsidiary of Pacific Marine. The company’s novel hullforms are tested in the open ocean in the waters off the Hawaiian Islands. Tank tests are also conducted at small scale to evaluate concepts. Computational fluid dynamics (CFD) analyses are undertaken using a supercomputer in Maui, which is the 12th largest computer center in the world, and Navatek also operates a 128- proccssor Linux cluster at its headquarters.
Navatek Ltd’s parent company Pacific Marine is a majority partner in Pacific Shipyards International LLC, Hawaii’s largest commercial ship repair facility, where a former US Navy SES has recently been converted into a Hybrid Small Waterplane Area Craft (HYSWAC) using a lifting body developed and tested by Navatek.
Funded by the ONR to the tune of US$18 million, the 48.75m (160ft), 30-knot-plus HYSWAC has a fullload displacement of 345 tonnes and was due to start builder’s trials in mid-August 2003, with performance trials on behalf of the ONR due to commence in October. If the trials are successful, it is understood that the lifting body technology developed by Navatek could be proposed by a number of’ the industry consortia bidding to provide the design for the US Navy’s Littoral Combat Ship (LCS).
The Navatek-designed lifting body was installed beneath the hulls of the former SES-200
The lifting body houses the drive train: engines, gearboxes, shafts, and Propellers
The HYSWAC is designed to confirm, on a large scale, the three major benefits of underwater lifting bodies verified on an earlier, small-scale 20m (65ft), 51 tonne Navatek lifting body demonstrator, Midfoil. Such, benefits are supported by extensive CFD studies conducted by the company. The advantages of the lifting body technology highlighted by Navatek include a superior ride in all seas, all headings and all speeds (including zero/loiter to maximum speed); higher transport efficiency at all speeds; and extended range/payload. The lifting bodies that Navatek specialises in designing are underwater appendages attached to the hull of the parent craft using struts. Having a cambered foil cross-section, a large planform area and low lift coefficient, they generate dynamic lift at higher speeds. Navatek’s project engineer Todd Peltzer says the lifting bodies reduce fuel consumption by dint of their high lift-to-drag ratio, and by reducing friction and wave drag. They also enhance seakeeping, at low and high speeds, due to their reduced waterplane area, the use of passive damping, dynamic control and careful selection of the parent hullform. The lifting body installed on the HYSWAC displaces around 163 tonnes as it has a volume of around 160 m3 (5,600 ft3), and measures 2m x 10m x 12.6m (6.6ft x 33ft x 41.5ft). Thus, it is large enough to provide a significant useable volume and can accommodate propulsors.
The former US Navy SES was selected as a suitable parent hull for the HYSWAC. During the two-year design and conversion process, Navatek removed the existing SES air-lift system and all related components, and installed the lifting body, which incorporates a new drive train (engines, gearboxes, shafts and propellers), all housed within it. The HYSWAC can be operated with variable immersion as speed increases, with the parent hull fully out of the water at maximum speed. An aft foil was also added for pitch stabilization and control, along with a proprietary advanced ride control system (ARCS).
