YACHT & POWERCRAFT DESIGN SERVICES

THE FUTURE FOR FAST CRAFT - SAIL & POWER by Stuart M Roy, RINA 1990

Extract from a report in Ship & Boat International, p16-17, December 1990

The meeting was chaired, and the first presentation made, by Stuart Roy in his role as Co-Chairman of the RINA Small Craft Group. He took as his theme The Future for Fast Small Craft - Sail and Power.  Roy opened by pondering the philosophical question of what is small and what is fast in marine craft, beginning with Peter du Cane's view that a small craft is one up to 150 feet in length and high speed is anything above 15 knots.  Now small craft are defined by different organisations in different ways: - vessels less than 150 feet in length, below 30 metres, below the size covered by the Merchant Shipping Acts, as covered by Lloyds Rules for the Classification of Yachts and Small Craft, perhaps as a craft in which all hull and internal systems can be designed and specified by one person, or a pleasure craft with a length between 2.5 and 24 metres.  Fast can also be defined in many ways, such as: - a maximum speed greater than 15 knots, a craft which normally planes, a speed capability in the top 25% of its type, approaching the maximum speed for safety, recently developed to give a higher speed, able to give an exhilarating ride or capable of time limited ocean passages. You pay your money and you take your pick.  One thing seems certain.  If 15 knots was fast in the 1950s, this is not the case now, with 30 knots commonplace in ferries and motor cruises, 40 knots in sports cruisers and foil assisted craft and racing power boats achieving in excess of 60 knots in up to 2 metre seas.  Roy remarked on the current boom in fast commercial ferries and then turned to the influence of record attempts, particularly the transatlantic speed record, on the design of power craft.

In the world of sailing craft, great progress has been made in high speed running with interest stimulated by the World Sailing Speed Record Council and the 500 metre course.  Currently speeds above 35 knots are recorded by multi-hulls; a 26.44 knot record stands for a C-class foil assisted catamaran and a stupendous speed of 42.9 knots was achieved by a board sailor, and there are undoubtedly more feats to come.  Sail boats are up there with the power boats.  Stuart Roy assessed a number of these record breakers in terms of the ratio of timed speed to wind speed, with ratios for the fastest boats from 1 to 1.74.  The question raised by some of the sailboards is whether air resistance is the limiting factor.  For example, Pascal Maka recorded a ratio of 1.74 in a 16-knot wind, but then, in a 40 to 45 knot wind, could only manage a ratio of 1, giving a higher absolute speed but a lower efficiency.  The next target is 100km/h or 54 knots.  Ocean passages with sailing craft have also seen some records broken, such as the 16.76 knots speed from Sandy Hook to the Lizard in a 75-foot catamaran.  Among competitive classes craft of sailing yacht, Roy identified the Whitbread Round the World races, the new America's Cup and the Open 30 Class as forcing the pace of technical development. On the power side, the SWATH concept, use of very slender hulls such as Ilan Voyager, stepped hulls, foil assisted multi-hulls, were all briefly examined and many of these proposals and actual craft have been reviewed in S&BI.  On sailing yacht keels Roy considered that, although there has been much interest in wings, end plates and slotted devices, these are the product of racing rules, or a need to operate in shallow water and that for really fast sailing craft high aspect ratio spade foil shapes will be favoured.

The EC directive for recreational craft is currently generating plenty of heat in the industry.  The proposed legislation is currently in a two-year period of consultation with interested parties and will cover the design and construction of recreational craft between 2.5 and 24m in length, through application of a common minimum safety standard.  Stuart Roy argued that although in some quarters it has been greeted with horror, in many ways this could be a positive piece of legislation, since the imposition of a common standard would be helpful in removing local homologation or type approval barriers which have in the past been used to protect certain markets from imported products.

A large market has emerged in 'fun' sailing, with catamaran, windsurfers or skimmer mono-hulls. It is estimated that there are some 500,000 people in the UK alone who are windsurfers and although the number of racing dinghy users declined in the early 1980s, this has now virtually recovered to previous levels.  The windsurfers can therefore be regarded as new entrants to the recreational craft market.  The question which Roy posed is will these windsurfers, having mastered the challenge of becoming proficient at sailing a board, move on to other types of recreational craft?  If so, what will they choose?  Fast and exciting recreational water sports offer many possibilities, from fast catamarans, jet-skis to the Open 30 Class, paragliding, speed sailing, one designs such as a new Laser development, and there is also the possibility of other ways of tempting the windsurfer moving on.

Gazing harder at the crystal ball, Roy considered the future will see greater overall speed under power and sail, gas turbine boats for record breaking trips, inflated semi-solid sails for speed attempts, faster ferries with attention to sea keeping, foils on everything, a diversification of 'fun' sailing, faster progress in sailing classes which can mount events with corporate sponsorship and media coverage, and better propulsion systems with a wider range of efficiency.  He concluded by urging attention to safety In small craft, particularly small fast power craft where a number of fatalities have occurred on the racing circuit.  He urged that it would be in the interests of the industry to have a good safety record, as it is worthwhile to keep a self-regulating profession.

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