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IX-515 Sea Flyer Hybrid Small Waterplane Area Catamaran (HYSWAC)

Sea Flyer is a unique hybrid lifting body ship that combines the high-speed capabilities of a hydrofoil and the rough-water stability of a small waterplane area twin hull (SWATH). A former Navy Surface Effects Ship SES-200 (IX-515), the vessel was converted in stages between 2000 and 2003 by Navatek, Ltd (a subsidiary of Pacific Marine and Supply, Ltd), with funding from the Office of Naval Research. Modifications included removing the existing air cushion system on the SES and all related components; installing a 170-ton underwater lifting body and a new propulsion system; adding an aft underwater cross foil and an advanced ride control system (ARCS) to control pitch and roll.

The lifting body allows the ship to operate with variable immersion as speed increases, with the hull completely out of the water's surface at maximum speed. In essence, the ship's hull is "flying" above the water while the lifting body, aft cross foil, and ARCS combine to provide lift and stability at high speed. This hybrid concept allows a larger payload than a SWATH, but with similar seakeeping capability. The lifting body on Sea Flyer also provides volume for propulsion machinery and contains two of the four control flaps for the ride control system. It is made of aluminum with composite materials used as side caps.

Sea Flyer was launched in June 2003, with Navy sea trials conducted in 2004. The current mission of Sea Flyer is to evaluate the sea-keeping and load-carrying capacity of a hybrid SWATH/hydrofoil ship incorporating an underwater lifting body and ride control system. During sea trials in 8- to 14-foot seas with 40-knot winds (Sea State 5), Sea Flyer was able to maintain an average cruising speed just one knot less than its calm water cruising speed. Sea Flyer also will be used to train the future crew of the Littoral Surface Craft-Experimental, also known as X-Craft, a high-speed catamaran currently under construction.

Sea Flyer is a Navy vessel (official designation: IX515) in possession of the Office of Naval Research. Navatek, a Hawaii-based company, signed a Cooperative Agreement with the Office of Naval Research in 2000 to design, reconstruct, test, and evaluate the vehicle. Navatek maintains operational control of Sea Flyer and has provided all operational crew to date.

Sea Flyer is a naval ship redesigned with underwater hull form technology that improves stability and speed. Under an $18 million contract, Navatek Ltd., a Hawaii-based company that researches and develops advanced ship hull systems, equipped the Navy's SES-200 ship with a 170-ton Navatek underwater lifting body that enables the hull to be fully out of the water at higher speeds. Navatek's patented technology is similar to that which NASA uses with spacecraft.

With the hull almost completely out of the water at higher speeds, there is a significant increase in stability over comparable vessels. There is an 80 percent reduction in motion, compared to a ship of similar size. This would improve the capability to land a helicopter on a ship smaller than 5,000 tons, approximately the size of a patrol boat and possibly a frigate-sized vessel.

Launched in June 2003 at Pacific Shipyards International, the 160-foot, 30+ knot HYSWAC has a full-load displacement of 340 LT. Sea trials of the new craft are ongoing. The HYSWAC is designed to confirm on a large scale the three major benefits of underwater lifting bodies verified through CFD studies and on the earlier, small-scale, 52-ton MIDFOIL.

Through its work on advanced hull forms for the US Navy's Office of Naval Research (ONR), Navatek has helped develop advanced Computational Fluid Dynamics (CFD) software and has become a world leader in the design, construction and testing of underwater lifting bodies. These lifting bodies can improve the performance of a broad range of conventional hull forms - including monohulls, catamarans and trimarans providing 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.

At zero/loiter speed, the added mass of the lifting body dampens motions, making the ship more stable, allowing for safer, easier deployment and retrieval of autonomous unmanned vehicles, equipment packages and personnel. At high speeds, the lifting body provides lift to partially elevate the hull out of the water (completely in some lifting body ship designs), significantly reducing hull drag. The lifting body lift-to-drag ratio is higher than that of the hull and, as a result, far less power is required to achieve speeds in excess of 40 knots.

The underwater lifting body also offers a third benefit. The additional displacement from the underwater lifting body can increase the monohull's payload by 15-20%, allowing it to carry more supplies, equipment, personnel, or fuel to increase its range of operations.

In 1998 the company launched its first lifting body ship, the 65-foot 52-ton technology demonstrator MIDFOIL, designed and built to demonstrate the performance advantages of advanced underwater displacement lifting bodies (overview). Her novel arrangement of a single, large foil positioned amidships and the lifting body itself are covered by U.S. patents. MIDFOIL's original configuration employed a thick two-dimensional foil fabricated of aluminum, with angled control fins located forward.

Further research and development resulted in an improved design: MIDFOIL was modified and refitted with a new lifting body and re-launched in 2000. In the modified configuration the original foil was replaced with a composite three-dimensional lifting body, the angled control fins were replaced with a centerline "T" foil, and an improved ride control system was installed.

Based on the success of MIDFOIL, Navatek received funding from the Office of Naval Research to convert an existing Navy Surface Effect Ship (SES) to a lifting body ship. Work on this $18 million project began in 2000 and resulted in the US Navy technology demonstrator craft called HYSWAC . The SES-200 provided the parent hull of the HYSWAC, reducing project costs.

ONR designed, developed and demonstrated a Hybrid Small Waterplane Area Catamaran (HYSWAC) by converting the Surface Effect Ship 200 (SES-200 IX-515) and incorporating an advanced lifting body to improve dynamic lift, payload capacity and small craft seakeeping. The HYSWAC project started with an FY00 Congressional plus-up and continued to receive congressional support with FY01 and FY02 plus-ups. A complete marine survey was completed prior to the SES-200 being towed to the conversion shipyard in Honolulu, Hawaii. Final design for conversion and initial concepts for the lifting body were completed. Lifting body final design, construction and installation were completed in FY03 enabling at-sea demonstration of the HYSWAC.

During the two-year project, Navatek removed the existing SES air lift system and all related components, and installed a 170-ton Navatek underwater lifting body incorporating a new propulsion drivetrain (engines, gearboxes, shafts and propellers) within the lifting body. This allows the craft to be operated with variable immersion as speed increases with the parent hull fully out of the water at maximum speed. An aft crossfoil was also added for pitch and roll control, along with a proprietary Navatek advanced ride control system (ARCS).



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Page last modified: 07-07-2011 12:52:48 ZULU