Life Expectancy of Dynex Dux Synthetic Rigging

12 Nov

It’s about time I concluded (well, for now) my little series on Dynex Dux synthetic rigging. I’ve covered my installation, the tensioning process, and what I see as the great potentials of a return to fiber rigging. As I noted in the last post these benefits depend largely on the ability of this new fiber to hold up over time to the substantial stresses of life at sea. So far that’s a question without a definitive answer- this material, in this application, is so new that its working life has not been conclusively determined. Actually, as sailboat rigging it’s still at a point where an Atlantic crossing is logged as milestone (See Sailfeed writer Andy Schnell’s article on switching to Dynex Dux). But this isn’t a new material, only a new use of a material that has proven itself exceedingly strong and durable in applications far more demanding than those found on a small sailboat. Still, in the marine environment everything eventually finds a way to snap, shear, or crumble, the questions are merely How, and When?

Before we get into that, I want to report a measure of success on my rig- I seem to have sorted out the tension issues I was having. My problem was a combination of not cranking down hard enough (as I suspected) and of fretting more than necessary – my father’s verdict was that I had things ‘just a little loose, but close enough’! Well, ok then. While my father was here we also added a toggle to the forestay. This took all of twenty minutes, thanks to my deadeye and lanyard setup. The deadeyes allow a huge amount of adjustment and are compatible with nearly anything that takes a 1/2” cotter pin so modification of the rig on the fly is an easy prospect.

The original setup. Can you spot the problem?
With the previous setup which we had whipped up in the shop the stay is able to rotate forward and aft on the deadeye but there is nothing to provide lateral rotation. This means any stress in a lateral direction falls as a side load on the stainless plates- a recipe for eventual failure.

The solution was simple, we just installed a toggle so that the attachment could rotate laterally. This was so quick and easy to set up that I’m now contemplating adding a turnbuckle as well to the forestay and backstay to help with pretension.

The new arrangement

But the point of this post was to talk about the lifespan of Dynex Dux, so let’s get into that now. If every material on a boat has an Achilles heel (and they all do, except, maybe, high quality bronze) Dynex Dux’s is undoubtedly UV. Like any synthetic material Dux is susceptible to UV damage and in most cases this will be what curtails its working life. It helps that properly sized Dux is much stronger than wire because it is sized for creep rather than breaking strength. It can therefore lose a good deal of strength before it is at risk of failure. For example, my boat was originally rigged with 1/4″ and 5/16″ stainless wire with breaking strengths of 6,900lbs and 10,600lbs. The Dynex Dux I’ve replaced it with is a uniform 7mm and has a breaking strength of 16,500lbs. This means the Dux will need to lose well over 30% of its strength before the breaking load falls even with brand new wire. Pull-testing by Colligo Marine has shown that UV does the most damage in the first year and that UV-damaged layer then creates a sort of shield that greatly slows the rate of degradation. So UV does of course degrade this stuff but it can take it, for a time. John Franta from Colligo Marine has this to say about the lifespan of their rigging: “For UV we are saying 5-8 years in the tropics but data is still coming in.” Not bad, for synthetic fiber, especially if it turns out to be the larger of those numbers.

At 16,500lbs breaking strength this shroud can withstand a good deal of UV damage before I need to worry.
Still, this is significantly less than the working life of stainless, which is not uncommonly stretched to twenty years despite recommended replacement intervals of half that. But even if they fudge the numbers on the wire a bit any prudent sailor with a stainless rig ten to fifteen years old begins to regard their turnbuckles, toggles, and other hardware with a healthy dose of suspicion. Unfortunately you can inspect these all you want (and you should!) but with old rigging hardware even a careful examination will not always turn up a problem before it results in complete failure.

While Dynex Dux may not last as long as stainless wire there is an additional measure of safety in a rig anchored with deadeyes- an advantage which is only available through the use of synthetic line. Contrast failure-prone stainless turnbuckles and wire end fittings to the strikingly simple anodized aluminum deadeyes and eyesplices which anchor my standing rigging.  Being of less corrosive material and without moving parts I expect these to serve me well over 15+ years. For the same reasons, I also expect that any potential points of failure will be far more visible than they might be with stainless hardware. Even if I add a turnbuckle or two to the system the ease with which they can be switched out for any similar piece of hardware will make prudent replacement intervals simple and affordable.

Simple, strong hardware

As the owner of a pocket cruiser this is what appeals to me about Dynex Dux rigging. The weight savings aloft are but small benefit on a boat like mine and I will miss the ease of turnbuckles and replacement interval of stainless. But what is the value of the added measure of safety and simplicity that comes with fiber rigging? If I go through two sets of Dynex Dux line in the same period I could have been served by a single set of wire rope I would consider this a fair trade for the added confidence in my rig, especially since when it comes time for replacement I can do all the work myself for only the cost of a spool of easily-handled line. With Dynex Dux when the time comes to replace a suspect shroud, stay, or the whole rig all that is required is to cut off a length and put a splice in either end, then repeat as necessary – no more tools are needed than for basic marlinspike seamanship (Confession: I haven’t learnt this yet, but it does not seem particularly difficult, merely time-consuming.).

Dynex Dux is best spliced with a modified Brummel splice, I am told

 Dynex Dux is also comparable in price or cheaper than stainless wire and the price is likely to drop as its use becomes more widespread. While UV is the limiting factor on the life of this new rigging and the numbers are still coming in, I do not expect that these numbers will limit its users to the racing crowd, or to those with deep pockets. Of course I’m no expert on the subject- at best a well-researched amateur- but there are plenty of professional riggers who give credence to this statement.

So if we make the reasonable assumption that Dynex Dux rigging will have an acceptable working life we must then ask how to determine when it is reaching the end of that life. Though rigging hardware can and does fail without obvious symptoms, we can at least take comfort in knowing that wire rope nearly always ‘strands’ before it actually breaks. Any sailor worth their salt will know not to place much trust in any part of their rig when one or more of the wires display broken strands.

A broken wire strand is a sure sign that the entire rig is unreliable

 Fortunately, Dux also scores high in this category. While it should be a good few years before I can report directly on this us early adopters have the assurance of no lesser body than the US Coast Guard that we needn’t worry about hidden damage. John Franta says:

 “We just got coast guard approval for our rigging on a day charter cat.  The Coast Guard statement is that it is the safest standing rigging available as it is fully inspectable.  The 2 failure modes are UV and Chafe,  both of which present themselves in visual cues, i.e. the line gets fuzzy.”

 Dux, like any synthetic line, makes wear and UV damage very visible by becoming fuzzy and frayed. I have seen the initial symptoms of this in my forestay, which is a bit tight on the bronze hanks of my sails:

John has assured me that this is nothing to worry about, reminding me that this forestay has plenty of strength to spare. He acknowledged that used with bronze hanks Dynex Dux is ‘somewhat consumable’ and we decided to leave things as they are, in part just to see how long they last. Wile hanked-on sails seems to put me in a small majority these days anyway those with hanks who feel less inclined to experiment could consider switching to ‘softies’- hanks (or shackles) made of Dynex Dux line. They can be bought from Colligo Marine or are easy enough to make (Colligo has a instructional video) the only downside is that unlike bronze piston hanks they can’t be opened one-handed.

A softie hank in action (Photo: Colligo Marine)

Other than this specific situation, excessive fears of chafe on Dux rigging seem to me unfounded. I can attest that this stuff is incredibly slippery and doesn’t easily chafe and have read many testimonials on its resistance to chafe when used in heavy industry. There is the possibility of a downwind pole or similar curtailing the life of a shroud but such wear will be obvious long before the rig is endangered, allowing a better setup to be put in place. With this rig chafe is certainly something to think about and keep an eye on but I don’t expect it to be a serious issue.

A more catastrophic risk would be something severing a shroud or stay but again the material is very hardy and to cut it would take a viciously sharp object flying around at high velocity and just happening to hit the rigging – an unlikely scenario which is bound to cause some sort of damage if it comes about. Dux could also be cut almost instantaneously with a sharp enough knife but not having any enemies to speak of I consider this more of a benefit than a risk. It’s nice to know that if it ever came down to it a crew member could easily cut the entire rig away in minutes.

I do have a nagging worry as to how my rig would fare in a lightning strike. Being susceptible to high heat I imagine that a direct lighting strike could heat the mast tangs enough to melt the rig right off the mast and bring down the whole shebang. That said, a strike which produced that kind of heat would destroy so many other things that I would be lucky if the boat survived, a situation in which losing the rig becomes just one of many problems.  Iit’s also nice to know that the lightning won’t have a convenient path to the cockpit through the backstay as it would with wire rigging. Still, I am curious to see what impact, if any, lighting strikes will have on boats rigged with Dynex Dux.

In the meantime I’ll just do what most every sailor does in the face of lighting- hope it strikes somewhere else! I remain confident that my new rig is ready for whatever the sun and sea can throw at it (at least for the next five to eight years). When that time comes up? Well if I’m still on this boat in all likelihood I’ll be ready to pull out a fid and a roll of Dynex Dux and splice up a new rig, wherever I happen to be. Which is precisely why I think this new material is going to be the next big thing for cruising sailors, even those on small boats like mine.

This article was syndicated from Safe At Harbour But Meant For The Sea: DIY Sailing with Paul Calder


  1. Duncan

    As a rock climber I learned to always beware whenever one line runs over another, due to potential for wear melting through. People have been killed by running their climbing rope through a nylon or dynmeema sling and then lowering off it – melts right through in no time. In general, having one piece of dyneema running over another seems like a bad idea, which is why the “softie” hank idea doesn’t seem so great to me. Also, since Dyneema has a relatively low melting point, better be careful with that BBQ grill on the stern, right next to the backstay!

  2. Chris

    Hey Paul,

    Been scouring the internet for information on Dynex Dux, you’ve shared some great information here and I’ve much enjoyed reading your posts. Any further thoughts on the longevity of the stuff now that you’re a year or so into it?


  3. Wolfgang E Bernardy

    Thanks for the great article. You may want to take a very close look at your bronze hanks. I can see how even the slightest burr or roughness could cause the damage pictured.

Leave a Reply

Your email address will not be published. Required fields are marked*. Comments are moderated and generally will be posted if they are on-topic and not abusive. For more information, please see our Comments Policy.

More from the AIM Marine Group