SPEED, MORE SPEED

Trends within the passenger ferry market show that the need for higher craft speed has been steadily increasing over the years and we now see catamarans that can sustain cruise speeds of 40 knots while carrying both passengers and vehicles. As ferry operators strive to satisfy the passenger’s need for speed to alleviate the pressures on their time, cruise speeds for new ferries will continue to increase. Additionally, payload densities are increasing, that is, we want to carry more payload on smaller platforms. Given these market trends, SES might well see resurgence in interest worldwide. We are already seeing interest in SES as potential hull forms for fast sealift and commercial RO/RO services. Once transit speeds exceed 50 knots, it can be very difficult for other hull forms to compete with the SES.

NEW CONCEPTS
One innovative and promising design that appears to incorporate positive attributes of the SES and catamaran concepts is the 90 ft catamaran surface effect ship proposed by the Harley Shipbuilding Corporation, Tampa Fla. A prototype is presently operational. According to a Harley spokesperson, the vessel would operate as a 150 passenger high-speed ferry between the Florida mainland and Key West. Among the non-traditional features of the Harley SES is its construction which consists of multiple layers of Kevlar with a linear foam core that is combined with aircraft epoxy. According to the company, the resulting structure is ten times stronger than an equivalent fiberglass hull. The combination of the catamaran and SES concepts is seen in the “catamaran lift” supplied by the deck between the two hulls and a “dynamic lift” created by running on the forward sections of the two hulls. The hull design, which has been patented, creates an aft air cushion which, according to the company, supports 85 percent of the vessels weight on the air cushion. The weight savings found with the vessels foam-cored, Kevlar construction combined with the use of conventional engines (four 1,050-hp Caterpillar 3412c diesels) and, another quite unusual feature, the surface piercing drives supplied by PSI Propulsion Systems, Inc., of Pompano Beach, Fla, add up to a claimed fuel savings of 70% (248 gal/h) as opposed to more conventional vessels, and an estimated cruise speed of 60 knots.

At that speed Harley also claims a 12-inch wake and a 12-inch draft. At idle the vessel will draw 3-ft.

Several supporting technologies, considered vital to the viability of the SES have also seen impressive growth over the last decade. Perhaps the two most important are waterjets and gas turbine engines. Both of these forms of propulsion are gaining greater acceptance within the commercial arena.

Commercial acceptance of the gas turbine engine is particularly important to very high-speed craft, as gas turbines provide the low weight to power ratio necessary to make high-speed craft commercially viable. Waterjets make a significant contribution to the success of high-speed craft as they eliminate, almost completely, the appendage drag component of the craft. The contribution of the appendage drag to the total craft resistance can be quite substantial once transit speeds of 50 knots or better are achieved.

KNEE JERK REACTIONS?
Naturally, along with the proliferation of high-speed ferry services comes the concomitant concerns regarding emissions. While EPA and state regulations are presently under development for marine engines—and will probably closely follow IMO requirements—at this time, however, emissions from marine engines are currently not federally regulated. Seizing on this regulatory hiatus, the Bluewater Network, a group of self-proclaimed environmental watchdogs, in July 1999, published a report claiming that ferries generate 10 times the emissions of automobiles and 25 times the emissions of transit buses. The Bluewater report was based solely on comparisons between San Francisco Bay area traffic across the Golden Gate between Larkspur and downtown San Francisco. Although a subsequent SNAME report cast serious doubt on Bluewater’s lack of data, methods, analysis, results and motivation, the report is often used as ammunition for those wishing to place roadblocks in the way of industry progress.

Innovative design, an emphasis on the use of low sulfur diesel fuel, and ongoing improvements to propulsion systems, not the least is continuous advances in computerized injection technology, are steadily contributing to the reduction of emissions. Obviously, the environmental responsibility of the fast ferry industry is increasing at the same rate of speed as the vessels––vigorously. ML

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