Ask Sail: Dynex Dux Fiber Rigging after 6,000 Sea Miles

When we were sailing from the small French island of St. Pierre off Newfoundland before making landfall in Crookhaven, Ireland, 2,000 miles to the east. At the time, Arcturus was the first boat to cross an ocean fitted with Dynex Dux synthetic rigging
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In July 2011, my wife, Mia, and I crossed the Atlantic in our yawl, Arcturus. We spent 23 days at sea, sailing from the small French island of St. Pierre off Newfoundland before making landfall in Crookhaven, Ireland, 2,000 miles to the east. At the time, Arcturus was the first boat to cross an ocean fitted with Dynex Dux synthetic rigging (see “Dynex Dux Across the Atlantic,” October 2012).

Three years on, I remember how difficult it was to sleep when we first set out, worried as I was about how the boat and rig would stand up, particularly since Mia and I had done the work on all the critical systems by ourselves. Would the mast remain upright?

Needless to say, the boat and her systems performed flawlessly, particularly the rig, which is what I was most concerned about. For the next two sailing seasons, we thought nothing of it, trusted it completely and enjoyed a double-handed North Sea crossing from Scotland to Sweden in 2012, and then a season in the Baltic last summer. I’m now fully confident in this new rigging material, which had its genesis in the Alaskan fishing industry and has since made significant inroads into sailing, cruising in particular, thanks mainly to John Franta and Colligo Marine.

Rig Design 101

Most modern cruising boats are equipped with 1x19 wire rigging, which I worked with extensively during my time as a rigger at Southbound Cruising Services in Annapolis, Maryland.

Breaking strength is the prime factor to consider in these situations. First, you must calculate the RM30, which is defined as the “righting moment,” or the amount of force in foot-pounds needed to heel the boat 30 degrees, using the boat’s beam and displacement.

However, while the RM30 serves as a good baseline for a rig’s normal working loads, few ocean-going boats remain within the realm of “normal working loads” under sail. Shock loads from falling off big waves, the added load of a knockdown or capsize, and other stresses all need to be accounted for, so a safety factor is added to create an RMmax. (Racers typically use a smaller factor to save weight, while cruisers use a larger factor for security.) These RM30 and RMmax numbers are then used to determine your wire diameter (and size all the other fittings in a boat’s rig, like mast section, spreaders, mast tangs and chainplates). Put simply, wire rigs are designed around breaking strength.

Dux, however, is fundamentally different, because the stuff is so strong you can ignore breaking strength. Instead, Dux is sized on creep. Creep, unlike stretch, which is an elastic deformation from which a material “rebounds,” is the permanent elongation of fibers over time under load. Like pulling taffy, Dux fibers that have crept will not rebound. If sized incorrectly, a Dux rig will eventually go slack under its pre-tensioned load.

To make sure this doesn’t happen, you need to look at a Dux creep chart. The key is to determine the typical pre-tension load carried by the rig, and the diameter of Dux that will not creep at that load. Again, strength is inherent—you’re inevitably going to end up with rigging that is far stronger than the wire it replaces. As a real-world example, Arcturus’s wire rig called for ¼in shrouds. Her Dux rig calls for 9mm shrouds— that’s a breaking strength of 7,300lb for wire versus 26,400lb for Dux.

Working & Sailing with a Dux Rig

Colligo Dux is marketed as “rigging reduced to its essentials,” and as such many riggers forego the use of turnbuckles in favor of old-timey (and cheaper) deadeyes and lanyards, like Colligo’s “Terminator” end fittings–solid aluminum thimbles, sized so that the radius of the eye-splice around them is large enough to avoid weakening the line.


A Dux end fitting on a lower shroud


“Old-timey” lashings are an option, but they make it harder to get in the right rig tension

However, before leaving the Canadian Maritimes I made the switch back to turnbuckles. An aluminum mast expands and contracts with the changing temperature, and with lanyards it’s impossible to get enough pre-tension in the rig to prevent it from going slack in the cold. This is true even on a small boat like Arcturus, and owners of all but the smallest boats should consider this before switching to Dux.

People have asked how often we need to tune the rig. “Doesn’t the Dux stretch?” they say. No, it doesn’t. Less than wire, in fact. “Doesn’t it go slack when it’s cold?” Only if you don’t tune it correctly. “What about when it sits for the winter?” Nope.

In fact, Arcturus sailed 2,500 miles to Northern Ireland, spent the winter on the hard there (with the mast up), then sailed another 1,200 miles up the west coast of Scotland, across the North Sea, down and around the Swedish peninsula and into the Baltic Sea as far as 60 degrees north, without us so much as touching a turnbuckle. After the initial tune in Baddeck—when I bought some galvanized turnbuckles from a fishing supply store—the mast remained in column and the rigging was snug all the way to Scandinavia. It wasn’t until we downrigged Arcturus at the end of the 2012 season that I made any changes.

Some Science

Coincidentally, that’s about the time I became curious as to how the rig was really holding up. In practice, I felt it was bulletproof. I’d figured out most of the chafing issues and knew how to fine-tune it. But what was going on inside the rope’s braid that I couldn’t see? How much strength was the sun’s UV rays sapping from our shrouds? Were my splices done correctly to ensure maximum strength?

To find out the answers to these questions, I got in touch with John Franta at Colligo Marine, and arranged to bring him two of Arcturus’s shrouds, a port upper and a starboard lower, which were light enough to pack in my luggage for the trip home from Sweden. I dropped them off, and he promised to do some pull testing for me and report back on the data.

“This is one of my least favorite things to do,” he wrote me in an email when the results came back. “Trying to make sense of real world data, that is.”

John went on to explain that there are a lot of variables associated with this kind of study. “First, you have the line, and the way it is manufactured and the manufacturer’s variables. Then you have the post-processing of the shroud or stay, splicing, cutting, end-fitting design and so on. You also have how it is handled, has it been kinked, folded, what about load conditions and cycling? Then you have the exposure variables: UV, temperature, moisture...” A heck of a lot to swallow, indeed!

John then proceeded to tell me about Arcturus’s shrouds specifically: “One shroud broke at 20,765 lbs-ft and the other broke at 17,692 lbs-ft.”

In other words, one shroud lost a hair over 21 percent of its original breaking strength (26,400lb), while the other lost just over 32 percent.

“The other data that we have shows this on the low side of the fitted curve. Average [breaking strength for 9mm] after about two years exposure is around 22,000 lbs-ft,” or a loss of about 16 percent.

But therein lies the beauty of Dux—even a 32 percent loss in breaking strength in the three years since fitting the shroud (and the thousands of miles it sailed) leaves us with a shroud that is still 8,292lb stronger than a brand-new piece of 9/32in wire! Our built-in safety factor, thanks to designing around creep, allows that same shroud to lose 65 percent of its strength before it approaches the strength of the wire it replaced.

Five Years Later

Last summer, I finally got around to replacing our galvanized turnbuckles with classy polished bronze fittings from Hayn. Otherwise, what’s it like to live with a Colligo Dux rig, now that we’ve had some experience with it?

In practice, I’m not losing any sleep over the strength of the rope itself. Franta’s pull-testing results confirm that. Although there are simply too many variables in play to explain the difference in strength lost between the two shrouds he pulled for us, the rig is still much stronger than a wire one.

Still, we control what variables we can. For example, I’m meticulous about splicing the ends. One thing Franta noted after his tests was that both our shrouds actually broke at new splices he had to put in. “Your shrouds were too long for the tester we used,” he explained, “so we had to re-splice one end of them.” This suggests that in reality, the shrouds, when fitted on the boat, were likely stronger than the pull tests indicated.

Franta has seen this before, but doesn’t have enough data to reach firm conclusions. For now, it’s a guessing game, and he speculates that re-splicing old line might decrease its life expectancy. Colligo’s estimate, which is intentionally conservative due to the lack of data, is that new Dux has a working life of 5-8 years in the tropics.

To protect my rig I also prevent chafe wherever possible, using tried-and-true methods like parceling and serving, just like they did on square-riggers—laying down a layer of black self-amalgamating rigger’s tape (the “parceling,” minus all the messy oil and cotton) and then wrapping it with tarred nylon twine, using a serving mallet to get the turns super-tight (the “service”).

Now that Arcturus is hauled out for upwards of nine months in frigid Scandinavia, we take the spars down each winter and renew this chafing gear at the spreader tips before re-rigging each spring. We also keep a close eye on wherever the sheets and sails touch the rig. Furthermore, our spreader tips are lashed to the shrouds with sail twine rather than seizing wire. All of this takes time and effort and knowledge.

At the end of each season I’m reminded why I like Dux so much. In Sweden, most boatyards are DIY, and many have fixed hand-operated cranes dockside. In the fall, folks take turns pulling their boats alongside and using the crane to pluck their masts before carting them over to a parking lot storage area.

Downrigging the boat and stowing all the shrouds (and on our double-headsail, double-spreader yawl, we have a lot of them) is an easy task. The standing rigging is decidedly lighter—a boon when sailing the boat, but especially noticeable when handling the rig in the fall. No fighting to coil up stiff wire rope, and I can hold all the shrouds from both masts in one hand. It’s that light. The shrouds spend the winter coiled neatly in the V-berth.

This summer, we’ll re-step Arcturus’s mast in Öregrund, a small coastal village north of Stockholm and plan to sail south and back around the peninsula toward the west coast. We’ll stage the boat near Gothenburg, some 700 miles from where she is now, in preparation for a run up the west coast and fjords of Norway. The goal is Svalbard by 2016. That will be year seven on the Dux rig, and, perhaps, an even greater test of its durability in the Arctic climate.

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