Design catalyst

The notion of starting a new project “with a clean sheet of paper” is certainly an appealing one, but in reality just about every sailing design effort starts out with a lengthy list of goals, criteria, schedules, and, yes, preconceptions. Moreover, most sailing projects are decidedly expensive, and those on the front lines know how difficult it is to make something 1% better, but how easy to make it 5% worse. As a result, sailing development tends to be cautious and incremental, only rarely taking a wild plunge into uncharted waters.

Given the evolutionary character of the design process, I contend that racing class rulesalthough often perceived as barriers to design innovationare actually an important catalyst for new developments. Psychologically, there is something about a legislated limit that impels people to seek clever ways around each “barrier.”

For a modest example, consider the popular Laser dinghy, a strict factory one design that requires sailors to rig their boats using the two basic vang blocks supplied as stock. Following the factory rigging diagram yields a meager 3:1 purchase, so for a long time sailors learned to luff momentarily as they stood up in the cockpit, bore down on the boom with one hand, and tensioned the vang tail with the other. More recently, however, all serious Laser racers have taken to rigging their vangs using the required two blocks along with 15 feet of slippery Spectra line and some strategically placed truckers’ hitches. These “macrame” vangs offer 8:1 power with surprisingly little frictionquite adequate for full adjustability while continuing to hike. Racing sailboats of every size must meet formal regulations imposed by race organizers, class associations, and, in most cases, government authorities. Seaworthiness is also, of course, a key consideration. Inevitably, sailors and yacht designers must exercise their intellectual creativity by working through a complex maze of rules and criteria that can be at odds with the search for pure speed. As a general rule, the more free-wheeling developmental classes such as the open 60s and Mini 6.5s will produce a more divergent array of potential solutions, simply because there’s a lot more latitude for experimentation. But by the same token, the most restrictive classes have become the arenas where the small-scale refinements are sweated out; and it’s often these seemingly minor improvementsin sail shape control, rigging systems, etc.that end up having the widest applicability.

Getting down to brass tacks, this article highlights two areas of developments that have recently emerged from the crucible of professional racing. Each reflects a need for creative solutions within the context of specific class rules. In addition, each has potential applicability in the realm of pure voyaging yachts. And not necessarily just the latest voyaging designs, either. The first examplestraight from New Zealand’s victorious America’s Cup programis a straightforward but ingenious rigging arrangement that could be used to upgrade many existing rigs.

America’s Cup 2000 was anticipated to be the year of the twisting wing mast. New Zealand’s dominating performance in 1995 had conclusively demonstrated the value of a large, extra-stiff mast section for better sail-shape control. Substantial “wing masts” that twisted into line with the air flow aloft were envisioned as the next step.

Of all the syndicates in Auckland, Young America appeared to pursue this line of development the most aggressively. Their rigs had the largest cross-sections, and just three pairs of spreaders instead of the usual four. Observers reported that the New Zealand defense appeared to be developing larger-than-average mast section.

What no Cup watcher apparently noticed, at least until the eve of the match itself, was the novel staying arrangement used on NZ-60the boat that ultimately defended the Cup. The Kiwi’s so-called millennium rig features diagonal shrouds that link each spreader tip to the opposite tip of the next highest spreader pair. The diagonal shrouds appear to pass through the mast along the way, but in reality each consists of two separate rigging elements attached to terminals on opposite sides of the mast. Presumably these terminals are tied to an internal reinforcing web that spans the mast tube and carries tensile forces diagonally along an X-shaped path.

The concept of linking windward and leeward spreader tips using diagonal shrouds is one of those brilliant “why didn’t I think of that” sort of ideas. Quite likely it’s been tried before, but for whatever reason it never became common practice.

Compared to a conventional rig, the Kiwi’s system effectively doubles the shroud angles and halves the lengths of the unsupported rig panels (i.e., the stretches of mast between shroud attachment points). The result is a significant decrease in the compression loads carried by each mast panel and a rig that’s considerably less prone to bowing out of column laterally. Wider, more effective shroud angles mean that tension on each shroud will be lower. This, in turn, permits a reduction in rod diameter for a modest savings in weight and windage (offset slightly by extra shroud length).

A particularly elegant feature of the tip-to-tip staying arrangement is the way that it puts the leeward rigging to work. In most rigs, the leeward spreaders and diagonal shrouds are essentially parasiticdead weight and wasted windage until the boat comes about and the loads switch sides. Although the Kiwi arrangement doesn’t eliminate any rig components, it employs them more efficiently, opening the door for performance gains in other areas.

Team New Zealand is doubtlessly keeping a few secrets for the next America’s Cup, but we can envision how the “dividend” associated with this novel rigging arrangement might have been “spent”:

1) To increase forestay tension without sacrificing mast stiffness or increasing rig weight.

2) To reduce mast weight (perhaps even to the minimum allowed under IACC rules) while retaining the stiffness of other fast IACC masts.

3) To increase safety factors and reduce the risk of mast failure.

Now that this particular cat is out of the bag, there’s little doubt that we’ll see similar rigging on many, perhaps all, of the next generation of Cup boats. As for the twisting mast scenario, the potential advantages have yet to be demonstrated. Aerial shots taken from directly above NZ-60 did not reveal significant mast twist.

Beyond the rarefied world of America’s Cup racing, the tip-to-tip shroud system makes good sense for a wide variety of ordinary boats. Quite a few mainstream voyagers from 1970s and 1980s have spreaders positioned higher on mast than they probably should be. Consequently, the lower shroud angles are uncomfortably smallsometimes as little as 9° to 10°. By converting to the tip-to-tip arrangement, compression loading in the lower portion of the mast could be reduced substantially, and an overly long lower mast panel divided into two short ones. The end result? A more stable, controllable rig with a greater margin of safety. Vintage IOR race boats are notorious for their delicate rigs, and, in many cases, would benefit greatly from this treatment. Indeed, almost any conventionally rigged boat with in-line spreaders is a potential candidate. In contrast to the winged-keel fad that swept sailing immediately after Australia won the America’s Cup in ’83, this cup idea has genuine and widespread applicability. Safer, quicker monohulls

It’s easy to envision how the amazing open class boats could serve as the prototypes for a future generation of fast ocean voyagers. So, it’s heartening to report that these boats have lately been developing in a generally more wholesome direction. After the disastrous 1996-’97 Vendee Globe, designers, sailors, and race organizers agreed to do something about a generation of wide, lightly ballasted boats that capsized easily, and all too frequently remained inverted. The lesson was repeated in the Around Alone when PRB, one of the “old model” 60s, capsized in mild conditions and failed to self-right.

Wide hulls are strongly encouraged in the open classes, thanks to a rule that stipulates a heel change no greater than 20° when moveable ballast is shifted from port to starboard or vice versa. In effect, this rule gives “double credit” for wide beam because greater beam is associated with higher form stability, which in turn allows more ballast to be carried to windward without exceeding the 20° heel limit.

Originally introduced as an expedient way to prevent water ballasting from getting out of hand, the 20° rule has, for all intents and purposes, rendered narrow boats uncompetitive. But, as it turns out, this may not be such a bad thing because it’s indirectly encouraging designers to develop a new and much superior breed of very wide boats. As a general rule, wide hulls provide more deck space and interior volume for a given price (the reason husky boats are so popular at the boat shows).

Open 60 class members and the organizers of the major solo races have, for the most part, agreed that these boats should exhibit positive stability up to heel angles of at least 125° with the moveable ballast centered. Another way to monitor stability is determining the righting arm at 90° heel. Some of the wide beam open 60s built prior to 1996 had a righting arm as low as 0.3 meters, which meant that the angle of vanishing stability would probably be exceeded before the mast even touched the water. In contrast, a new-generation open 60 such as Catherine Chabaud’s Whirlpool(Marc Lombard design) has a righting arm of 1.2 meters at 90°. This four-fold improvement in righting moment has been achieved in part through weight savings in the hull and rig, but primarily by hanging more ballast at the tip of the deep swing keel.

Viewed from above, the modern open class boat is roughly wedge-shaped, with the maximum beam point about 65% aft and extended all the way to the transom. The central underbody is quite flat, and the bilges are fairly firm because this shape ensures favorable treatment under the 20° rule as described above. Heeled to 25° or so, the waterline beam narrows considerably, reducing wetted surface and wave-making drag. Daggerboards needed

Unfortunately, when a wide, wedge-shaped boat heels to its sailing lines, the axis of the immersed underbody becomes misaligned with respect to the axis of the keel. In effect, the keel will be constantly trying to drag the boat to leewardnot the happiest of situations for upwind efficiency. For this reason, many open class boats now have a pair of retractable, outward-canted daggerboards located just ahead of the mast. For upwind work or close reaching, the leeward daggerboard is extended to provide the necessary lateral resistance. The main keel, whether canting or fixed, becomes little more than a strut to hold the ballast bulb away from the hull.

Once the ballast keel is relieved of the lateral resistance role, it can be shifted much farther back in the boat without hurting the helm balance. With a wedge-shaped hull, this will help control bow-down trim and greatly improve tracking on broad reaches. Viktor Yazykov’s open 40 Wind of Change (Stephen Baker design) was among the first to demonstrate the benefits of mounting a keel considerably behind the boat’s midpoint. Built on the proverbial shoe string, this remarkable flyer not only kept pace with the 50-footers during much of the last Around Alone, but on one occasion achieved a 239-mile day’s run with the skipper lying injured below and no working autopilot. These are, of course, precisely the kind of sailing manners that would be welcome in any bluewater voyaging boat.

In conclusion, the open class rules have pretty much dictated broad, wedge-shaped hulls, which at one time meant challenging boats with often dangerous sailing characteristics. Over time, however, designers and sailors have devised ways to make these beasts a great deal safer and more tractable. It’s an ongoing process, and the best is surely yet to come.

Contributing editor Sven Donaldson is a freelance writer and former sailmaker.

By Ocean Navigator