Are new rigs voyage ready?Jan 1, 2003
Bluewater sailing inevitably means an intimate, sometimes emotional relationship with spars, rigging, and sails - the gear making up a yacht’s primary propulsive system. Sailors tend to have strong opinions about various rig alternatives. Whether grounded in experience and sound logic, or misunderstanding and prejudice, these opinions are genuinely important, because once you point the bow to sea, you’ve got to have absolute confidence in all your essential sailing equipment.
For most sailors, the best possible confidence builder is the knowledge that numerous other sailors, perhaps entire generations of sailors, have set to sea with similar gear and, with few exceptions, come through fine. No doubt this conservative attitude has slowed the evolution of sailing equipment, but it’s entirely understandable given that few amateur sailors would willingly volunteer for the role of nautical test pilot.
On the other hand, there are strong indications that the sailing world has reached an important crossroads now that a new generation of rather unconventional rigs is beginning to show its full potential. This article presents an overview of the “state of the art” in offshore-capable rigs - everything from recent trends in series-built aluminum to the latest experiments with rotating and free-standing wing masts. Certainly when evaluated in terms of all the usual criteria, such as sailing performance, potential reliability, maintenance requirements, and overall user-friendliness, a number of the more avant-garde rig concepts merit a closer look.
Rig weight and safety
It’s generally true that beefing up a hull to make it stronger and tougher will result in a safer, albeit slightly slower, offshore boat. However, it’s misleading and potentially dangerous to apply the same rationale to rigs. Naturally, every important rig component needs to be sufficiently strong and durable not to break (particularly considering that most stayed rigs, like the proverbial chain, are only as strong as the weakest link). But excess weight aloft is also highly undesirable and, in some cases, downright hazardous.
Weight aloft is harmful in three ways: First and most obvious is its negative impact on lateral stability. A heavier rig not only reduces a boat’s ability to “stand up to her sail” but, more significantly, reduces her limit of positive stability - the heel angle at which a capsizing moment takes the place of righting moment. True, the heavier rig will increase the boat’s rotational moment of inertia, possibly reducing the likelihood of being bowled over by a breaking rogue wave. However, it’s unlikely that any naval architect would seriously consider increasing rig weight for this reason alone - the downside is simply too great.
Other drawbacks of excess rig weight are linked to the so-called “pendulum effect,” the tendency to exaggerated pitching, particularly when driving into a head sea. Severe pitching is unpleasant and exhausting, and it increases the risk of personal injury or falling overboard. The exaggerated fore-and-aft movements of the rig also induce abrupt fluctuations in the apparent wind that disrupt the smooth flow of air across the sails and degrade boat speed. Rig fittings, especially those near the masthead, experience greater shock loads and can suffer accelerated fatigue failure. In short, a serious offshore sailor needs to be quite sensitive about rig weight. This is an area where sound engineering and adequate, but not excessive safety margins are clearly preferable to over-building and redundancy. By the same token, the modern practice of loading up the mast with several radio antennas, radar scanner, wind instruments, masthead lights, a big radar reflector, and two or three sails, permanently set on furlers, may not always be such a great idea.
Requirements for satisfactory offshore rigs go far beyond weight control. For one thing, spars and standing rigging should be evaluated in terms of aerodynamics. A lightweight and structurally reliable rig is nevertheless unsatisfactory if it causes excessive turbulence and aerodynamic heeling force.
In addition, a good offshore rig needs to function efficiently in wind speeds from less than five knots to more than 50 knots and to perform satisfactorily on every point of sail. Ease of reefing and sail handing and a bare minimum of potential chafe points rank high on the list of essential rig attributes. Having a rig that’s reasonably easy to climb is also a benefit, although equipment is available to overcome most obstacles in this regard.
Established solutions, incremental gains
Extruded alloy spars got a boost start from the metal aircraft industry of WW II, and by the ’60s had largely supplanted wood. Today, aluminum rigs are a mature technology, although minor evolution continues to take place. In recent years, the most obvious trend has been a shift to aft-swept spreaders. This design idea was originally developed for fractional rigs, but is now increasingly popular with masthead ones as well. Swept spreaders contribute extra fore-and-aft stability to a rig, eliminating “pumping” problems and, more often than not, the need for running backstays. For a growing number of modern, performance-oriented boats, a combination of long, swept spreaders, outboard chainplates, and non-overlapping headsails permits some very worthwhile reductions in mast size and weight, even without recourse to expensive carbon-fiber construction. The “secret” here is simply widening up the shroud angles to reduce mast compression; in this way, a mast section with thinner walls or smaller outside dimensions can safely carry the loads.
However, the shift from in-line to aft-swept side rigging is not entirely clear sailing because these new-style rigs don’t have much tolerance for improper tuning. Swept spreader rigs need to be set up tight (generally much tighter than many sailors realize) and with the correct balance between pre-tension on the uppers and the diagonals. Swept spreader rigs also generate impressive bending loads at the spreader roots, which need to be addressed through well-engineered base fittings. Third, the aft-swept shrouds and spreaders tend to exacerbate chafe problems when the mainsail is eased for broad reaching and running - the most common points of sailing for offshore work aboard all but the fastest boats. In short, the swept spreader solution, although quite workable in most cases, is not a dramatic step forward for most voyaging sailors.
Stepping up to carbon
Over the long run, it seems likely that carbon composite rigs will eclipse metal ones, much as aluminum has largely displaced wood. In terms of physical properties, carbon simply has too much of an edge to ignore - a much greater advantage than the benefits offered by aluminum over wood. Depending upon the grade of carbon fiber and the fabrication techniques used, finished carbon composites are typically three to four times stiffer and more than twice as strong as 6000-series aluminum on a pound-for-pound basis. And because composite structures are built up using numerous, thin laminations, it’s relatively easy to achieve additional weight savings by tailoring a carbon mast so that highly loaded portions contain the most material. By contrast, nearly all alloy masts are produced from a single, uniform extrusion; meaning that a mast which is “strong enough” at deck level will inevitably be overweight aloft.
The bottom line is that a full-rigged, carbon-fiber mast for a typical mainstream voyaging boat will come out 30% to 35% lighter than an aluminum one equipped with identical standing and running rigging. Moreover, the carbon rig will have a slightly lower center of gravity due to greater weight concentration in the lower panels. The effect on stability and sailing characteristics is often dramatic. Slicing 150 pounds out of the 500-pound rig of a mainstream 45-foot yacht will increase stability about as much as adding half a ton to the keel while reducing (rather than increasing) the overall displacement, rigging loads, and pitching tendencies.
Unfortunately, carbon masts are considerably more costly than aluminum ones due to a stubborn triple combination of costlier material, extra labor, and more involved processing. The price gap may narrow a bit in years to come, but will not likely disappear. To appreciate the challenges involved, I’ll briefly describe the building process as I observed it on a tour of Hall Spars in Bristol, R.I. - one of the world’s premier suppliers of carbon-fiber rigs.
Hall builds its spars on precisely tapered aluminum mandrels that serve as male molds. Pre-preg carbon-fiber tapes are applied to the surface of a mandrel and consolidated using proprietary techniques. The majority of the fibers are laid down at 0° (parallel to the spar’s axis) with a small proportion wrapping around the spar at 90° or, in certain situations, at intermediate angles.
The pre-preg carbon materials favored by Hall (and the majority of the other leading composite-spar builders) arrive at the shop already impregnated with special epoxy resins that are formulated to cure at elevated temperatures. However, they will still cure (albeit slowly and poorly) at room temperature. To extend shelf life, they are normally shipped and stored frozen. At room temperature, thawed pre-pregs feel tacky rather than wet. Most builders like them better than dry reinforcements and liquid resin because they are relatively clean to handle and easy to position.
The pre-preg’s chief drawback, of course, is the need to cure it at elevated temperatures - anywhere from 150° for “low temperature” types to around 250° F for “high temperature” varieties. To avoid distortion problems, large parts such as masts must be warmed very uniformly, a delicate process that requires specialized equipment.
Hall Spars is one of several mast builders that has invested heavily in autoclaves, essentially giant pressurized ovens, to improve the quality of its composite parts. Autoclaving is essentially a souped-up version of the vacuum-bagging now widely used in fiberglass molding operations. Using vacuum alone, the maximum possible clamping pressure is one atmosphere (a bit less than 15 psi), and anything over 10 psi is rarely achieved. By contrast, the autoclave at Hall Spars normally delivers 90 psi. At this high pressure the carbon fiber laminate is crushed against the mandrel while it cures, ensuring uniform resin distribution, eliminating voids, and reducing overall laminate thickness by nearly half.
These “bakes,” as they’re called, are tricky operations. The autoclave must be charged with nitrogen because ordinary air at 90 psi and 250°F could support the explosive combustion of the laminate and its plastic wrappings. Fans inside the autoclave help keep temperatures uniform as the electric heat is “ramped up” gradually and then cooled down with equal care.
Dealing with details
Fulfilling the potential of carbon composites depends on achieving optimal fiber orientation. This is due to the fact that uni-directional carbon quickly loses its superior physical properties if loaded even a few degrees off-axis. For the most part, stayed masts are straightforward compression tubes, but special situations arise when stress paths must deviate around cut-outs for sheave boxes, spreader bars, etc., and at high-load points such as rigging tangs, goosenecks, and masthead cranes. The most sophisticated carbon rigs feature beautifully sculpted composite sub-assemblies that are either bonded to the mast tube or fabricated in place using additional layers of oriented reinforcements.
At the other end of the spectrum, a basic carbon tube can be fitted out with conventional metallic gear in very much the same way that the typical aluminum mast blank becomes a finished spar. A number of companies have been working on ways to mass-produce mast blanks using either automated braiding machines or other variations on the pultrusion process (manufacturing “composite extrusions” in bulk by drawing bundles of resin-coated fibers through a die). The aim, of course, is to lower the cost of carbon spars enough to access the broader market. The downside, of course, is a diminished weight advantage - the main reason for going with carbon in the first place.
On the plus side, any carbon mast will be immune to those irritating corrosion problems that occur when stainless hardware contacts aluminum. Composites are easier to paint than aluminum, and the paint tends to last longer before it needs repainting. More equivocal is the lively debate as to whether carbon masts are significantly more vulnerable to lightning damage than their aluminum counterparts. The high electrical resistance and relatively low heat tolerance of carbon laminates would certainly appear to make them more vulnerable in event of a strike. On the other hand, the high conductivity of an aluminum mast may make it more likely to attract a strike in the first place.
Rotating masts and carbon construction
Despite the obvious aerodynamic advantages, rotating masts have only recently reached a state of development that makes them a viable option for ballasted monohulls. Historically, the wide staying base and generous lateral stability of a multihull platform were considered prerequisites for this style of rig. French soloist Yves Parlier can be credited with the first successful open 60 project to incorporate a rotating wing mast - in this case an arrangement stayed by shrouds led far outboard to the tips of long deck-mounted spreaders. Parlier’s superior reaching ability with Aquitaine Innovations convinced several other open 60 competitors to emulate his rather cumbersome arrangement despite reliability problems, inherent restrictions on the use of overlapping headsails, and the obvious difficulties that crop up when coming alongside.
Very recently, some high-performance monohulls have successfully moved away from the deck spreader system in favor of either hinged spreaders at midmast height or “semi-stayed” masts with much-reduced dependence upon side rigging. The latter represent a fundamental departure from deck-stepped, rotating masts because they blend the mechanical characteristics of cantilever beam masts (Laser dinghy or Freedom 40) with those of a conventional, compression-only spar.
Taken to its logical extreme, the semi-stayed, rotating mast will shed its remaining rigging to become an unstayed rotating rig. But although simple in principle, building workable rigs of this sort still presents major engineering challenges. Nevertheless, some innovative designers and builders have lately achieved results that bode very well for the future.
Unstayed rigs come of age
Today’s unstayed, rotating rigs owe a lot to the round-section, unstayed rigs developed by Garry Hoyt, Mark Ellis, Eric Sponberg and Yves Tanton. Successful production boats by Freedom Yachts and Hinterhoeller (the Nonsuch catboat series) demonstrated that unstayed rigs could be a viable option for mainstream, offshore-capable yachts. In some cases, they also helped to establish the credentials of carbon-fiber masts during an era when this material was, to a large extent, banned from yacht racing.
As a dedicated sailing futurist, Garry Hoyt has long argued that stayed rigs are a throwback to the bi-plane era - a compelling notion, but one that tends to minimize some key differences between sailboats and aircraft. However, it’s been nearly three decades since the launch of Hoyt’s original Freedom 40 cat ketch with its thick, free-standing masts and rather uninspiring upwind abilities. We’ve finally reached the point where the all-around performance of the latest unstayed rigs is drawing level with most of the conventional alternatives. More important, these free-standing rigs are often coming out ahead in terms of functionality and overall user-friendliness. Unstayed rigs tend to bend in gusts, automatically de-powering the mainsail as needed. They greatly reduce boat maintenance because the usual assortment of toggles, turnbuckles, tangs, and wires - each a potential failure point - is entirely eliminated. Provided the engineering and construction are right to begin with, an unstayed rig should normally last the life of the boat.
But even with the latest advances in carbon construction, it’s so far not been possible to build free-standing wing masts as light as their stayed counterparts. On the other hand, the difference isn’t great, and in most cases will be largely offset by a lower center of gravity. As for relative cost, the extra carbon required, particularly to reinforce the butt portion of the unstayed rig, is offset by the absence of spreaders and standing rigging.
A major breakthrough in unstayed, rotating rigs for voyaging yachts came out of Britain when Carbospars Ltd. unveiled its AeroRig in 1991. This is a tapered, cylindrical mast with an integral cruciform yard that serves as both the mainsail boom and a forward-projecting strut to support the jib tack. The entire rig swings on two large bearings mounted at deck and keel level, respectively.
On a broad reach, the AeroRig really comes into its own because it can rotate and maintain optimal flow across the sails. By contrast, conventional rigs lose efficiency because the sails stall and the mainsail often blankets the jib. Thanks to a counter-balancing effect, an AeroRig gybes more gently than a conventional rig - definitely a worthwhile safety feature. Sail areas can be reduced by reefing or roller-furling (provided the main and jib are reduced in concert). The AeroRig is also reputed to deliver extraordinary control at low speeds and in close quarters.
AeroRigs have now been used successfully on a wide variety of boats from mega-yachts to production hulls by Beneteau and Catalina. But despite their proven virtues, it isn’t difficult to envision somewhat simpler, more aerodynamic unstayed rigs based on pivoting, foil-shaped spars.
Peter Goss’ wonderful but ill-fated Team Phillips catamaran featured two such rigs, one for each hull. Developed primarily by Barry Noble and Martyn Smith, who worked alongside the project’s chief designer, Adrian Thompson, the two 135-foot wing masts were based on huge, tapered carbon-fiber tubes with external fairings, and a free-floating mast-track system to accommodate mast bend. Ultimately these amazing rigs were evaluated a lot more thoroughly than the boat itself because one rig was tested on shore for several months while the big cat’s broken bows were undergoing a total rebuild. Aside from a relatively straightforward bearing problem that was cured before Team Phillips departed on her final, disastrous voyage into the heart of a North Atlantic storm, the rigs gave every indication of working very well indeed.
On a more down-to-earth scale, Eric Hall, co-owner of Hall Spars, has built three unstayed wing mast prototypes for a J/90 sportboat. This lively 30-footer has proven an excellent benchmark because several sisterships with standard rigs are actively raced in Hall’s neighborhood. Unlike either the AeroRig or the Team Phillips spars, Hall’s “Blackwings” have true airfoil mast sections, not a simple cylindrical or modified cylindrical masts. The first two versions were sloop-rigged with running backstays for better headstay control. However, the third is a so-called “uni-rig” - essentially a super-efficient cat rig with all upwind sail area concentrated in the mainsail but with provisions to set an asymmetrical chute for off-wind work. Experience with iceboats and high-performance catamarans has established that a wing-mast uni-rig is potentially more efficient than a sloop with equal sail area. Hall’s 30-foot Blackwings have shown good speed against similar, conventionally rigged boats, and plans for similar commercial rigs are now in the works.
Another interesting variation on the unstayed theme is represented by the work of the young French designer Juan Kouyoumdjian. During the last America’s Cup cycle, several syndicates experimented with twisting rigs as a way to gain some of the benefits of a rotating spar without running afoul of Cup Class rules that prohibit this feature. Under the International Measurement System (IMS), the same restriction applies. So, Kouyoumdjian dreamed up a 50-foot “rule-beater” that received credit for the drag of side rigging although it had no side rigging, and gained extra unmeasured sail area from its huge, twisting wing mast. Krazy K-Yote Two caused an enormous outcry at the 1999 Admirals’ Cup and, in the end, never raced. Now, however, Kouyoumdjian is back with a 61-foot voyager/racer that features a more advanced, but similar rig. The structural core of the twisting wing mast is a cantilevered, carbon I-beam enveloped by carbon-reinforced fairing panels. Fiber orientation is tailored to make the rig relatively stiff, both laterally and fore-and-aft, while allowing the topmast to twist off as much as 20°. Close-hauled or close reaching, it seems quite possible that a twisting wing mast of this sort could out-perform a “normal” rotating mast that lacks any provision to match the angle of attack to the local wind sheer. Someday, the ultimate may be a wing-mast rig that can twist and rotate simultaneously.
In any event, we should soon be learning more because the Kouyoumdjian 61 is currently nearing completion at Rhode Island’s Goetz Marine Technologies and should be racing this summer. It’s just one more indication that the “standard” sailing rig is entering a round of change.