Soft rigging for voyagingAug 6, 2010
During a break while delivering a catamaran in the Baltic Sea this summer, I took the opportunity to walk the length of the marina in Cuxhaven, a small town on the Elbe River in Germany. The boats tied alongside were the usual mix of Mom, Pop and dog cruisers all enjoying a perfect summer sailing the North Sea.
One boat, however, caught my eye. The boat itself was no different from the rest; a slab-sided fiberglass monohull with plenty of interior space and a spacious cockpit. It was the rig, and rigging, that held my gaze. Instead of the sturdy looking 1:19 wire commonly used on production cruisers, this boat had a spindly high-tech mast held up by some equally spindly high-tech rigging.
I knocked on the hull and a tall, handsome German man appeared. We talked about his rig. He was an engineer, and a sailor, and while he acknowledged that his boat was no racing machine, he told me that the change in the boat's rig had made a big difference to his sailing pleasure. By his estimation he had saved about 30 percent of the overall weight of his original rig. Without all that extra weight aloft his boat heeled less and more importantly to him, since he usually sailed in the North Sea where the shallow water kicks up a short, steep chop, the boat pitched significantly less.
This all got me thinking. First it was interesting to once again see that new technologies pioneered on the extreme racing edge slowly trickle down to the rest of us average sailors.
And second, I wondered just how much of an application high-tech rigging would play in the sailing pleasure of most voyagers. Would there come a time when formerly exotic Vectran shrouds and Spectra running backstays were as commonplace on a small cruising boat as the now ubiquitous roller furling gear?
Traditional wire rigging
Most of us are familiar with traditional wire rigging. These twisted strands of stainless wire with swaged end fittings have held up our masts for decades, mostly without incident. Why then consider anything different? Before you plunge into the world of high-tech rigging and decide if it's right for you, let's take a look at some of the forms of rigging currently in use.
There are three most common types of wire rigging; the 1:19 stainless wire, a seven-strand wire and Dyform, a relatively new type of wire rigging. The ratio 1:19 refers to the fact that the wire is made up of 19 small wires twisted together to form one strong wire. While this kind of rigging has been in use for decades, it‚Äôs not without its drawbacks. The strength-to-weight ratio renders it only applicable to cruising boats and those racing classes that insist on the cost saving of traditional wire. When measured against a high-tech piece of rigging, wire is bulky, heavy and stretchy. The stretchiness comes from the twisted wire trying to untwist as a load comes on it. That, along with some inherent "give" in the wire strands themselves, means that new rigging has to be adjusted over time to compensate for the stretch.
In order to adjust wire rigging to keep the right tension on each piece of rigging from the longest cap shrouds that run in some cases from deck level to the top of the mast, to the shorter "diagonals" that lend support to the mast column itself, turnbuckles are used. These turnbuckles can be made from a variety of metals such as bronze, chrome plated bronze or stainless steel. Use a good waterproof grease such as Lanocote to keep the threads lubricated. For stainless steel screws in stainless bodies a grease containing molybdenum disulfide should be used. This is extremely effective but be aware, the grease is black and could stain your sails.
The wire, end fittings and turnbuckles all add up to a hefty package with lots of windage. For those who care not about performance, but want reliability at a reasonable price, this is the rigging for you. Those sailors who are looking for a bit more performance from their rigging can consider rod rigging. Instead of strands of wire, the rigging is made from cold drawn Nitronic-50, a nitrogen strengthened austenitic stainless steel. This metal has higher concentrations of chromium, nickel and manganese than regular stainless steel giving it much better corrosion properties. The strength to weight ratio of rod rigging over wire is significant, as is the amount of windage since the rods are much smaller, for an equal strength, than their wire counterparts. There is some initial stretch in rod resulting in the use of turnbuckles to keep the rigging properly tensioned. Rod rigging is sized according to its rated breaking strength and is measured in pounds. According to Navtec, one of the companies that produces a significant amount of the rod rigging found on boats, the prefix "-" is called the "dash size" and is placed before the rated strength in thousands of pounds. In other words a -12 (dash twelve) rod has a rated strength of 12,000 lbs.
Made from yarns, not metal
Rod and wire still dominate the rigging market, but their share is steadily being eroded by some new, innovative and highly engineered rigging, the so called soft rigging. This rigging is soft because it is made from yarns rather than extruded metals and is manufactured in a completely different manner. Instead of a single material being used, a composite piece of rigging can be made from any number of different materials, in any number of forms. Just as the sailmaking industry before it, the rigging industry has discovered many choices of high tensile yarns that when properly engineered can result in low stretch rigging with incredible strength-to-weight ratios. This new rigging has revolutionized the racing market and proven its reliability in extreme offshore conditions such as the double-handed Barcelona World Race and the Volvo Ocean Race.
Let's take a closer look at the makeup of soft rigging. There are three main parts to it; the inner core, the outer covering and the terminals. The inner core yarns are the load bearing yarns and can be whatever the engineer deems best for each particular application. The most common yarns are Vectran, carbon, PBO and Kevlar. Each of these yarns have their strengths and weaknesses and each piece of rigging is engineered with these differences in mind. For example, Kevlar, PBO and to some extent Vectran are all extremely sensitive to UV degradation. Their tensile properties are amazing, but as soon as any light comes into contact with the yarns there is immediate degradation. This problem is alleviated by encapsulating the delicate yarns in an outer cover that serves three main purposes; to protect the inner yarns from the elements, to bundle the lot together into a length of rigging and to provide a rugged chafe protective covering so that the rigging can withstand the abuse of a tough offshore passage.
Navtec has been at the forefront of soft rigging. In 1997, they pioneered PBO rigging in a product called Z-System. The "Z" stood for Zylon, another name for PBO. By bundling PBO strands together in differing amounts, the engineers were able to precisely customize a specific piece of rigging to meet its needs. This kind of precision means that the size of each piece of rigging is kept to a minimum, an important consideration given the drive to reduce windage. The cost is also kept down. The individual yarns are expensive. Precise engineering means that there are no extra yarns along for the ride in any given piece of rigging.
For the outer cover, Navtec uses a woven Technora. Technora is impervious to sunlight and is highly chafe resistant. By weaving the outer cover you are able to create a surface that, when tensioned, bears down on the internal fibers giving the piece of rigging its desired rigidity. This outer braid protects the delicate inner fibers from sun and moisture. The ends are created from a carbon composite that binds the outer braid and the inner fibers around a titanium thimble to seal and protect the piece of rigging allowing it to be attached to a mast or deck fitting.
Tackling the same issue of creating a lightweight, extremely low stretch piece of mast rigging, the Composite Rigging division of Southern Spars has taken a different approach. Instead of PBO or Kevlar as the load bearing yarns, Composite Rigging has engineered its cutting-edge rigging using bundles of carbon fiber in a product they call Element C6 (EC6). The EC6 cables are made from bundling 0.043-inch-diameter pultruded T800 fibers sheathed in a jacket that can be made from a variety of different fibers. The T800 carbon yarns are what they call an intermediate modulus fiber, meaning that it is engineered to provide the optimal combination of strength, stiffness and stretch resistance. One of the weaknesses of carbon is that the wrong modulus can result in yarns that are too brittle for standing rigging.
The outer cover serves to protect the delicate carbon yarns and to provide the piece of rigging with chafe resistance and overall durability. One of the fibers that Composite Rigging uses for its covers is Spectra, an extremely rugged yarn that resists abrasion and withstands UV and humidity better than most other yarns. In some applications Southern Spars will use a regular polyester braiding for the outer cover. They also produce cabling with a braided stainless steel cover.
While all these different engineering techniques, each claim superior stretch resistance and strength-to-weight ratio over the other, it would seem as if the EC6 product does have an advantage when it comes to windage. The carbon yarns are extremely strong, meaning that fewer individual yarns can be bundled together to make a single piece of rigging, resulting in an overall smaller diameter for the rigging. On a racing yacht where there are a dozen or more pieces of standing rigging holding up the mast, the accumulated benefit over a long passage makes a big difference. The drawback, however, is the prohibitive cost of carbon.
One of the great benefits of soft rigging is the ability to precisely engineer a product that meets a variety of different requirements. The engineer can consider not only the perfect blend of yarns, but also the budget of the person buying the rigging. It may be that for some applications an extreme, cutting edge product is not necessary. The requirements may be more modest and less expensive load bearing threads that can be used along with a basic polyester cover rather than Spectra or Technora. The result is still a light, low-stretch piece of rigging. Someone looking to trick out their sailboat with higher technology than wire is not saddled with carbon as their only option.
Where heavy old fashioned turnbuckles were used to attach wire rigging to the deck and to allow for some adjustability, new sleek, low windage turnbuckles are being used for the soft rigging. Add to that the archaic steel shackle is no longer seen aboard a high-performance yacht. Instead the riggers have gone even further back in time for a solution. Soft rigging is usually tied together with a lightweight lashing, a means of attachment that was used on old clipper ships. The result, however, is a cheap, extremely reliable and super lightweight means of accomplishing the same thing.
Just as roller furling needed to go through a few years of intense testing in some rough sailing environments before the equipment was deemed suitable for the rest of us to use with full confidence, soft rigging will also need to prove itself. Indeed it has already proven itself in some of the most extreme environments. The Open 60 Paprec-Virbac had EC6 for standing rigging for the gruelling Barcelona World Race, a double-handed sprint around the planet; non stop. The rigging was returned to the manufacturer for a complete test once the race was over and the results were remarkable. With the exception of a cut in the cover of one of the shrouds the rigging was in great condition. There was no discernable degradation in either the strength of the rigging or in its stretch resistance.
To illustrate the performance gains by using the EC6 system, consider that the carbon rigging is a quarter of the weight of an equivalent strength rod rigging. Consider that the Barcelona World Race is 29,000 miles long and physical weight savings coupled with most of that weight being over 50 feet off the deck along with the significantly reduced windage and you start to see a cost performance benefit that knows no equal. The same can be said of Navtec's PBO rigging as numerous boats competing in the last Vendee Globe used the latest custom engineering from Navtec without failure. If anything is keeping sailors from upgrading to high-tech soft rigging, it's the cost, not reliability.
Brian Hancock has recorded 250,000 offshore miles. His most recent book is Grabbing the World.