Ocean Magazine : 1 May June 2005
30 | ocean E-MOTION 61M Asian superyacht owners, whose ranks include Fuglsang's client, have long been seeking solutions to pitching and yawing in a seaway, and to instability when at anchor. One went for active and passive stabilizers in his latest 52m Frank Mulder-designed Sea Shaw, combined with anti- roll ballast tanks when not under way, which is the conventional wisdom in Europe and the States. Another opted for sheer size in building his 60m aluminium La Baronessa at Palmer Johnson in Sturgeon Bay, Wisconsin. Yet a third chose the tried and tested explorer design when he had the 38m Sinbad, lately cruising in Australia and New Zealand, constructed at Delta in Seattle, while a fourth made a somewhat more radical departure in launching his 88m proa Asean Lady from the Yantai Raffles yard in northern China last year. Fuglsang's "e-motion" concept is different again. "The long slender center hull allows a smoother entry into a seaway, greatly reducing wave noise and slamming", he says. "This, combined with four ride control foils, substantially reduces the yacht's motion, both underway and at anchor". The active foils are very large, each about 5 square metres. They span between the side hull and the center hull, two on either side, and are individually controlled by a VT Maritime Dynamics ride control sensor and electronic package. In sea trials so far, White Rabbit exceeded her contracted 17.7 knot speed by two knots in light trials, and fully loaded averaged 18.75 knots for a two-way run. At 49 per cent power, cruise speed was 16.1 knots, enabling a 5,000 nautical mile range with plenty to spare. In initial 1.8- 2 m seas, at 18 knots and with the ride control system active, the vessel's roll was reduced by 57 to 75 per cent, depending on the heading, and pitch by 25 to 55 per cent, compared with when the system was in passive mode, said Fuglsang, citing VT Maritime Dynamics figures over four test circuits. Even when not active, the effect of the foils is still significant in dampening down motion. "She handled very nicely", her experienced French captain told us later. Direct comparisons with monohulls are difficult unless similarly-sized vessels are trialed in the same sea conditions, but simulated studies show that a trimaran yacht, at 20 knots in a 2-2.5 m bow quartering sea, will have 50 per cent less vertical acceleration than a similar length monohull.
2 July August 2005