The ‘A’ Class Catamaran – Its place at the top table.
At 18ft long with a total allowed rig area of 150ft2, but weighing in at a mere 75kg, the ‘A’ Class is very much a Formula One car in catamaran form and in the last few years, developments have seen this class take off more than ever before, quite literally.
Anyone with an interest in the hi-tech aspects of sailing will probably know something of the ‘A’ Cat. If you have visited the RYA Dinghy Show over the last 5 years, you will have seen one. They are spread worldwide with large fleets in Australia, USA/Canada, throughout Europe and there is even a growing fleet emerging in Argentina. They have had some 55+ years of open design resulting in them now being amongst the most highly developed small sailing boat classes on the planet.
Originating from a desire in the late 1950’s by the IYRU (Later renamed ISAF and now World Sailing), to encourage racing and design development of catamarans. They proposed four classes with simple size criteria based on length, beam and sail area, and crucially, with minimal design rules. These were simply named A, B, C and D classes. The ‘A’ class is by far the largest remnant of the four classes. The ‘B’ class was a 20ft twin hander with 235ft2 of sail and developed into the Tornado and a few offshoots such as the F18. The ‘C’ class was another twin, but at 25ft with a 300ft2 rig, has become a super sophisticated monster and the pinnacle of small cat design that races for the Little America’s Cup. The ‘D’ Class was 32ft and a sail of 500ft2 with three crew, but rapidly dwindled away.
Various designs for the ‘A’ bubbled away until the IYRU held trials to seek out the best designs in the ‘A’ and ‘B’ classes and to award them international status. At the Catamaran Club on the Isle of Sheppey in 1967, the Tornado won the ‘B’ class, and in the ‘A’ class category the British Unicorn competed, along with with several other boats, against Graham Johnston’s Australian Australis design. At that time the spec was simply to be a single-handed cat with sliding seat or trapeze restricted only by length, beam and sail area. The Australis design won and gained international class status. However, the Unicorn design still gained popularity in the UK and Europe. It eventually became a strict one-design class with rules on hulls, weight and mast diameter, which accounts for the vastly different sail shapes now seen on the two boat designs. Today the Unicorn still measures and is still accepted as an ‘A’ Class cat.
So, the free reign given within the ‘A’s development class spec allowed several other designs to arrive, each an attempt to improve on the other. All modern designs can trace their evolution back to these early boats in one way or another. Many home built designs turned up, and home building of ‘A’ Cats continues today, particularly in the USA, where home building tends to be more popular.
As building and materials technology improved, the stitch and glue plywood built and the glass fibre built boats, in order to save weight and get down to the absolute minimum, needed to be made with the strength only in certain high load areas – shroud plates, beam mounts, foil cases etc., This resulted in the class getting a bit of a reputation for being fast but rather delicate. Gradually these materials gave way to the carbon foam and carbon nomex sandwich construction.
Fast Hull Shapes
The Australis hulls were pointed at both ends similar to a canoe, in an attempt to produce a drag-reducing hull. The designs were often determined by the materials available and nowadays space age construction techniques are possibly one reason that the modern boat is now becoming increasingly popular, as it is producing immensely stiff and strong yet light boats, capable of withstanding hard racing for several years.
Currently, the modern ‘A’ cat bears a striking resemblance to its rather higher profile cousin, the AC45 . The distinctive Dreadnought shaped bows of the ‘wave-piercing’ hull design reduces the pitching moment when in waves. The hull is essentially upside down when compared to many boat hulls. The widest part is towards the bottom with the result that the hull won’t sink as far before the buoyancy starts to push it up again so floats higher. They also tend to have the beams bonded in making it a very stiff one-piece unit. Hull sections and profiles continue to change. The requirements of a boat designed to foil mean that the underwater hull shapes are starting to be optimized for lighter wind sailing, as the hull should be out of the water when it is going fast in a higher wind.
On the latest 2016 boats, aerodynamic drag is now recognized as increasingly more important as the airflow over the boat, with the added apparent wind, can sometimes be as high as 30 or 40 knots. Beams are now aerodynamically streamlined, smoothing the airflow over the drumskin tight trampoline. Double skin trampolines are also a new design feature. Previously the underside of the tramp was a mass of ropes, chords and bungees. Now these are sandwiched between two airtight skins. On one new design, the Holland Composites DNA, even the tiller bar is now streamlined to match the rear beams curved profile!
There are several elements key to the ‘A’ cats speed and success. Over the last 15 years much work has been done on the design of foils (rudders and daggerboards). Initially the foils were all straight as the technology to make them anything else, without risking failure, was simply not available. However, they could be put in at an angle and canted towards the centerline. This seemed to give a little lift to the boat, thus making it faster by reducing the drag of the hull when the boat was heeled and flying a hull. They were also made slimmer and longer, and this higher aspect ratio vastly improved the drag effects over a broader chord foil. Then in 2005, Dutch composites expert and sailor, Pieterjan Dwarshuis, raced in the Worlds with a C shaped foil. This supplied much more lift and helped in getting the windward hull flying when going downwind – doing ‘the Wild Thing’ as it is known in cat circles. And, as the leeward foil curved under the boat more, it produced much more lift as the angle of attack (Rake) could be adjusted also. Result – particularly when combined with small winglets on the rudders was that the boats went faster. Within a couple of years these foils became more commonplace and by 2008 German sailor, Bob Baier, had won the European championships using a set.
However, some feared that complex hydrofoils could possibly be fitted to the boat, rendering it fast but impractical and expensive. So in 2009 a rule was brought in with the intention of preventing this hydrofoiling from happening. The now famous ‘A’ class ‘Rule 8’ stating that all foils must be inserted from the top of the hull, and that there must be a minimum distance between the tips of the bottom of the boards of 75cm from the centreline. That seemed to do the trick and for a few years things went along nicely. But the foil building technology steadily improved and a consistent way was found of producing extremely strong shaped daggerboards from carbon composites. In 2013 the foils had developed from a C shape into a J shape and as a result of redesigned rudder winglets, positioning them at the bottom of the blade, the boats started leaping about like salmon. So the next logical move for this development class boat was obvious and was to make it fly. The boat has about the same power to weight ratio as a foiling Moth so it was assumed that it should be able to fly, but for one crucial potential problem – Rule 8. This meant that conventional L shaped boards, similar to the AC boats foils, are not class legal. But thinking around corners is what designers and sailors like to do and before long, designs for foils emerged that complied with the top insertion, limited span restrictions and provided enough lift to get the boat clear out of the water. A movable rake system allowed the angle of attack of the boards to be varied combined with fore and aft movements of the crew weight. The real turning point came in 2014 before the Worlds in New Zealand.
Many of the America’s Cup crews are also ‘A’ cat sailors. In fact the most successful ‘A’ Class World Champion is the ETNZ skipper Glenn Ashby.
The ETNZ America’s Cup team took delivery of half a dozen ‘A’ cats and set about with gusto seeing how far they could be pushed. Improved, redesigned and strengthened boards and rudders started flying around the world on express carriers as they broke and re-broke the foils in an attempt to push the boat to it’s limits. It worked and the boats started to fly, albeit in the hands of these sailing superstars, but techniques were discovered for getting the boats foiling for longer each time. As a result of this, Glenn Ashby won yet another world title. This paved the way for the current developments.
Optimized designs, where daggerboard positions and beams are moved slightly, and newer, more stable foil sections that have lower drag are now arriving, with a Z and J/Z shaped board proving more stable when combined with T or L shaped rudder tips. However, the holy grail of upwind foiling is still being worked on. And this is all still done within the restrictions of Rule 8. The top insert only rule has prevented earlier, more stable, and probably easier foiling to happen if an L shaped main foil were to be fitted. However, the very fact that it is less stable probably results in a faster boat and the need to raise windward foil, as would be the case of the higher drag L foil, is unnecessary and something a single-handed sailor’s workload can do without.
The ‘A’ class rules allow you to do anything as long as the total area, including the mast, does not exceed 150ft2. This area has traditionally seen the greatest developments in the past. Shape is entirely up to the sail maker based on mast shape and flexibility. The original masts were flexible tapered affairs as still seen on the Unicorn today. But in the early 1980s the ‘A’ class moved more towards an untapered wing type mast which was able to be rotated, somewhat like the leading edge slat on an aircraft wing, and thus create the sail shape more efficiently and to adjust it to cope with the windspeed changes created by the apparent wind. Techniques developed and composite masts began to appear in Europe about 25 years ago. The sails design paralleled the mast designs.
Initially they were fully battened but conventionally tapered towards the head. Then, in the mid 1980s the ‘Fat Head’ sail appeared on the ‘A’ cat for the first time. This lower drag high-aspect ratio rig, much like a glider wing, allowed and helped the boat to fly a hull much earlier downwind with the resultant reduction in drag. Upwind, powerful 12:1 downhaul and 9:1 mainsheet systems could flatten the sail and when the carbon mast arrived, this was even more efficiently achieved. As the sail area is the determining factor, not the shape, variations were tried at various times. Really ‘Fathead’ sails, with the heads at over 1000mm were the thing for a while. These required the leech to be cut away in a concave manner to conform the area rule, but now the more popular ‘800’ head offers a good compromise of power and heeling moment. Rigid wing type rigs were also seen occasionally. Back in 1978, at the European championships, a wing sail proved unbeatable in light winds. More recently designers, such as the US mast maker and ‘A’ cat ace Ben Hall, have experimented with a wing sails. But, their practical handling off the water still proving troublesome.
The most current sail development is the ‘Decksweeper’ sail. This is a sail that uses the trampoline as the end plate, making it more efficient, similar to winglets seen on airliners. The sail has its centre of effort lower down, and thus reduces the heeling force created by the fatter head sail and is ideal for a foiling design. The byproduct of this is that going upwind, where any heeling force, above just flying a hull, is not wanted with either foil design, is that it feels like you have another gear. Now much more of the power is pushing you forward. And this is usually sufficient to compensate for the higher drag created by the more complex shaped foils with their higher surface area. So, faster uphill, faster downhill, what’s not to like? However, the downside is that when it’s not foiling conditions, the decksweeper is less powerful and thus the C board, or ‘Classic’ boat is still king.
The decksweeper was first tried on the ‘A’ cat in 1987 in Australia but proved to be unbeneficial compared with more conventional designs. It was tried again a few years ago, by former World Champion Mischa Heemskerk, who was interested in exploring it again on a more modern boat design. The trials were inconclusive and the project was shelved for a while. Then 2015, in the search for more power but with less sideways pressure, as required by a foiling boat’s need to be sailed flatter, he reappeared with one at the 2015 Dutch Nationals and wiped the floor with everyone, including Glenn Ashby, who was there getting ready for the Worlds a few weeks later. But you can’t keep that friendly little Aussie down for long. When he arrived at the Worlds, he’d simply chopped one of his older sails down along the leech, and sewn an extra bit onto the bottom to reach the tramp. This was enough to get him back on track speedwise, and in a variety of conditions, he managed to beat Heemskerk by an increasing margin each race to retail his World title.
Much design work was done over the winter of 2015/16 and two of the major manufacturers both produced more optimized designs. The Polish Exploder came out with their Ad3, with a design input from the Spanish based D3 Applied Technologies design team. The other was the Holland Composites DNA F1 design. A radical looking boat with advanced aerodynamic features and a fully carbon fabric stiff trampoline. Both designs have proved to be game changers and with little to choose from as regards performance. Misch Heemskerk won the 2016 Worlds on the F1 with Darren Bundock 2nd on the Ad3. Both designs foil earlier and are more stable when doing so making them easier to control. It would appear that the design curve is starting to flatten out again now as regards hull and foil design with these two boats setting the standard of performance.
The ‘A’ Class Future
The two foil types are causing a little debate within the class though. Although all the boats measure as ‘A’ Class cats equally, the foiling/floating thing appears to irk some in a few national class associations. Some want separate races for foilers, claiming that is not fair now to race both on the same course. A movement to start a ‘Classic’ class of non-foiling boats has been suggested. But, most associations simply prefer to split out the results and run a parallel results system. And, at those lighter wind events, or in areas like Southern Germany, you don’t hear many complaints.
New foiling boats arrive and older second hand straight or C board boats find ready new homes with some being converted to a foiling configuration with new foil cases and rudders, whilst others are sold to the encouraging number of new sailors entering the class. This is often the best place to start, as it’s not actually a hard boat to sail initially. (The class has a minimum of 5kts and max. limit of 22 kts of wind for racing) Beautifully fast and responsive yet without many of the unpleasant characteristics that some other cats will catch you out on, e.g. the long bows tend to reduce pitchpoling. The added benefit of being 75kg makes it really easy boat to handle ashore; a true single hander, the only thing where you might need someone else’s help for 2 minutes is with stepping the mast.
The next jump looks like it will be in rig design. It’s open design rules means that it will continue to see innovation and development within its rules as yet more ways are found to make them go even faster. Their ability to be altered, modified and improved will also continue to see the ‘A’ cat being used as a test vehicle for design ideas on larger boats. Who knows what is around the corner designwise, but the ‘A’ cat should be able to meet the challenge.