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Swath/Hydrofoil Hybrid Presented At Fast '95

Hybrid hydrofoil monohulls (HYSWAS) combine hydrostatic and hydrodynamic lift, in effect, merging Swath and hydrofoil technology. Conceptual studies have been carried out in Germany for a 500-ton passenger car ferry design of the HYSWAS type. Preliminary studies have found that the design is favorable when compared to other fast ferry designs if the owner's concerns include operating on long, exposed routes (such as the North Sea or the English Channel), and preventing speed losses due to waves and good seakeeping.

The excellent seakeeping behavior of the HYSWAS makes it an ideal candidate for fast service on exposed routes according to its desingers. Consequently, the first design is anticipated to sail a relatively short route on the channel for example, on the Oostende - Ramsgate (72nm/2hr.) service, where hydrofoil boats (Boeing jetfoil) are already employed.

Future routes include longer trips such as the Vlissingen - London route, which would measure about 134 nm and four hours long.

The vessel under study has a full-load displacement of 500 tons, a cruising speed of 39 knots in three meter waves, and a maximum operability in waves up to four meters. The vessel is designed to carry 80 cars and 350 passengers, to a maximum range of 500 nm. The INCAT 74-m wavepiercing catamaran has a similar combination of payload and speed. However, the HYSWAS will be designed and equipped with a comfortable passenger area and with a restaurant to keep passengers comfortable on longer routes.

GENERAL LAYOUT Two versions of the vessel are currently under investigation, the diesei-powered Mark IV and the turbinepowered Mark VI. The two versions differ in several aspects related to the propulsion plants and the design of the foil systems. The present design incorporates an "airplane-type" foil configuration and a longer strut capable of supporting a rudder behind the propeller. This configuration was chosen because: An internal investigation at the Hamburg Ship Model Basin came to the conclusion that investigated canard configurations perform worse than airplane configurations due to down wash and other effects; • Yamanaka et al. (1991) deal with the hydrodynamic effects at the aft foil of a tandem foil configuration. Large changes in flow direction at a foil positioned aft of a forward foil are described. The magnitude of the effect causes lift of the aft foil to decrease by 60 percent at design speed and to even less at lower speeds.

• Conventional airplanes are optimized for long range performance and to avoid down wash of wings or stabilizers positioned in the front. The main wing then operates in "clean flow." Canard configurations are found in fighter airplanes and missilesto provide maximum maneuverability.

• The roll/heel stabilization of HYSWAS can be best performed by a main foil of as much span as pos- sible. Therefore the span of the main foil shall be maximized. Mark IV has a cantilever main foil. Mark VI has a main foil with struts at its tips to reduce drag and to maximize roll stabilization by larger profile chord and higher lift slope near the tips.

The Mark IV is the latest stage of EMIT's HYSWAS developments, and is designed to be powered by a pair of MTU 20V 1163 TB73L diesel engines of approximately 13,000 kW. At 90 percent MCR, the available shaft power after the rear gearbox is about 11,400 kW and fuel consumption 206 g/kWh. The thickness of the strut shall make it possible to remove the engines through the machinery pit which has an inner breadth of at least 5.6 ft. (1.7 m) over 32.8 ft. (10 m) length.

The Mark VI is designed to fit two Allison 571-K liquid fuel gas turbines mounted side-by-side. The thickness of the rear strut shall make it possible to remove the engines through the machinery pit, which has an inner breadth of at least 3 ft. (.9 m) and a useful cross section area of more than 4 sq.-m. for the gas turbine's fresh air and exhaust fume ducts. The rated shaft power of the two engines together is 11,400 kW. At a realistic service rating, the available shaft power after the rear gearbox is about 9,300 kW, fuel consumption 251 g/kWh. As gas turbines are not designed primarily as economical operators at low ratings, an additional propulsion system is required to supply the propulsion system power for low speed. Also, according to preliminary calculations, 9,300 kW is not sufficient shaft power to achieve 39 knots. Therefore MTU 8V 396 TE 74L diesels rated at 1,000 kW are designed to be installed on each side near the strut to drive a traction propeller via z-drive through the side strut. The traction propellers are mounted where wing tip and side strut join and reportedly will supply excellent maneuverability. SEAKEEPING CHARACTERISTICS MARK shall be able to pierce regular waves up to 13.1 ft. (4 m) high. Piercing means that heave, pitch and roll motions can be kept to a minimum, if not zero. When MARK encounters regular waves higher than 4 meters, the ride control system will switch from piercing to contouring mode.

Contouring waves of 16.4 ft. (5 m) seems to be the limit of passenger acceptance. Therefore, the maximal operational seaway for MARK was defined by a significant wave height of four meters, when the probability for occurrence of waves higher than 5 meters is less than 5 percent. Draft on foils was selected so that the propeller would not emerge in the trough of a 4-meter wave. Also, submergence of re- tracted side floaters and slamming of the wet deck will be avoided in 4- meter waves.

Along with current technical studies, in collaboration with the Bremerhaven based Design Laboratorium, new concepts are currently being investigated for: superstructure design; passenger compartments; and efficient loading and berthing of fast vessels.

These studies will lead to additional modifications, particularly in the area of the superstructure and the interior design of the vessel. General aspects of improving passenger transportation at sea will be central to these studies.

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