The Offshore Voyaging Reference Site

The Unknown Unknowns


Andy’s recent two posts on Dux high modulus rope rigging were fascinating. He did a great job of communicating his enthusiasm, without being a fanboy blindly extolling the virtues and ignoring the drawbacks of a product, as you see so often on the Internet.

He also wrote that he would explain:

why [Dux] can be considered to have already passed John’s 20-year field test.

And that’s what I want to explore in this post. But first, understand I’m not writing this to set some young whippersnapper straight. In fact, I have huge respect for Andy’s opinions.

That said, my rule in question is probably the one that has contributed most to our track record of successful voyaging—in 25 years we have only altered, or even delayed, our plans once due to a gear failure*.

Here’s my rule:

If your primary goal is to get out there and stay out there voyaging, don’t install any gear on your boat, at least if it’s mission critical, that has not been in common use for at least ten years and preferably twenty.

As you have probably guessed by now, I believe that high modulus rope standing rigging (Dux or otherwise) does not pass this test. Read on for why.

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Drew Frye

I built chemical plants for many year. Unreliable = unprofitable, but 50 year old tech also = unprofitable. So every time I was trying something new. Perhaps it been used somewhere else and adapted. Perhaps I’d run a pilot plant. Perhaps the engineering was well understood and it just wasn’t really much of an unknown, just a change. Mostly I was right, and a few times I was not. But I always left myself a way back. Some reasonable way it could be fixed during a scheduled shut down. A little “hidden” capacity or some manner of adjusting the process later. And you can bet that anything mission critical got special attention; not just discussion, but real testing and real contingency planning. Over engineering is traditional!

I think the same applies here. In the case of Dyneema, it’s generally practical to go way over strength and flog chafe to death. Inspections increase with new gear; that is part of the science. With some gear you will always carry a spare anyway. Sometimes traditional gear is really pretty poor even after 20 years. Safety gear, for example, is so seldom really tested that some stupid designs became traditional. Certain inflatable PFD and jacklines designs come to mind. So we inovate when the status quo is unimpressive.

But yeah. I just finished an article on repairing sails with adhesives, which included a good bit of lab testing. The a few days later I hauled my genoa down and spent 4 hours on hand-stitched repairs. Yeah, I just trusted it more.

Stein Varjord

Hi John and Drew

I think you have very good points, of course. I like to go properly into the experimental zone of new solutions, often trying to develop new ideas. Working on racing boats that’s necessary. But most ideas don’t live long, even in the mind. I assume one of a thousand “good ideas” prove to actually be good, and mostly are quite small steps. And I’m quite proud of my creative thinking ability. 🙂

Without actually using it here, you both point to an English word I’m fond of: Redundancy. Preferably all critical elements of a boat should have a backup. If something fails, it will not make significant other damage and it will be easy to get up and running again. On racing boats, which are still my measure for optimum functionality, one always try to apply Johns “both belt and braces” rule unless that’s gonna slow the boat significantly.

Look at the Vendee Globe Race going on right now. Solo, nonstop, round the world, no assistance, 60 foot extreme boats cruising steady over 20 knots. Now close to Cape Good Hope. Fascinating! The leaders have lifting hydrofoil wings. “Rock star” sailor Alex Thompson on Hugo Boss has been leading for about ten days. Some days ago his sb wing hit something in the water and broke off. Very bad, but the boat also has the normal daggerboards, so he’s now not loosing ground. Redundancy. Soon he can gybe and fly on the port wing.

The main reason i prefer rope rigging is exactly the possibility to have more redundancy. It is more vulnerable to chafe, etc, but also shows any such problem clearly before it fails. (Steel doesn’t). It’s light and affordable enough to have more spares. It’s very much easier and quicker to exchange worn elements. Many key spots will allow doubling up without much penalty. For me, a complete sailing nerd, rope rigging is way more reliable than a steel version. For sailors who are not into inspecting the boat continuously, i think steel rigging is more reliable and will remain so for some time…


Good post. On the subject of synthetic rigging we recently chatted with a rigger in New Zaealand where we currently have the boat. He mentioned that he had recently resigned two boats that had tried synthetic rigging and had suffered an unacceptable degree of deterioration from chafe and perhaps UV. Our wire rigging is still going strong after 17000 ocean crossing miles and 7 years use.

Eric Klem

Hi John,

Well said. I worked on the other end of what Drew discusses when I was designing industrial machinery and it was really interesting to see how plant managers viewed our stuff. We could develop a new model that would save them 10’s of thousands of dollars a year in energy costs with extensive reliability testing and they had no interest in installing it unless we installed an old proven model right alongside ready to start up if the new one had any issue. Understanding their thinking has been very helpful to me and has helped a lot with knowing what to buy and what spares to own.

On the other hand, I think that sailors can get too obsessed with tradition or what the local chandler is selling and end up with a far from great solution. I fabricate a lot of my own stuff because I can’t bear to buy something which I know is flawed and will likely break at a bad time. I do my best to fully understand the requirements of what I am building but sometimes the flaws don’t show up for quite a while and they are not at all what I would expect.


Rob Gill

Hi John,
Rumsfeld’s quote possibly originated from the JoHari Window : which has been around for many years as a model for examining problems and seeking solutions in many fields, including the US military I suspect.
The wonderful thing about the Johari Window, is it outlines a simple but powerful concept for sharing of ideas by people with different viewpoints and levels of understanding. In doing so, the so called “Arena” window pane for the parties becomes larger, the “Blind-Spot” and “Facade” become smaller. Sometimes serendipitously the “unknown-unknowns” become “known”, simply through open Q&A and free sharing of information.
A bit like this site really!

Edmond Rees

Hi John

thanks again for your earlier assistance! Made it from Toronto out the St. Lawrence to Newfoundland and then down to NS where we left the boat in Chester Basin for the winter. Epic sail for us!

So, next question, near Montreal we ran aground hitting the bulb of the keel at 6 kts – stopping the boat dead. No water and no stress cracks in the bilge and the bolts look fine.

No after hauling we see the strike and more questionably the more obvious gap between the keel and the hull. Is this a matter of just filling in the gap and recoating the bulb or should we be more paranoid? Unknown unknown… 🙂


Ed Rees

Keel gap 1.jpg
Stein Varjord

Hi Edmond,

To know exactly what the situation is, a thorough investigation is needed, but from your description I would certainly drop the keel and look at all relevant areas with renewed suspicion. 6 knots to full stop is a lot of force. The fact that there is a gap is definitive proof that there has been movement and something has changed.

That again means that something might have been weakened (or not, but it needs to be checked), and that there is now room for more movement. That’s never good. The keel needs to be seated with zero room for movement and minimum flexibility. There’s no way one can fill the gap well enough without dropping the keel, even if all structural elements were to be totally fine.

From my armchair it’s easy to tell others to do big jobs on their boat, 🙂 but in this case I actually think this is urgent. In my opinion, there’s no other option than:
– Drop the keel
– Check/reinforce the hull
– Check/change keel bolts
– Reseat the keel properly.
– Sail with a good feeling the coming years! Good luck!

Edmond Rees

Thank you both – will do right now.

Edmond Rees

Thanks again John – Marley Field performed an investigation of the keel just now and gave it a clean bill of health! Checked the rudder as well and no issues there either.

Absolutely relieved on this end and really appreciate you connecting me to the right guy to make it easy to execute – perfect!

Edmond Rees

and the second picture to match…

Bob Hodges

I’m going to add a belated reference point to this thread regarding Dux and Dyneema rigging solutions. Like John, I am a small boat sailor at heart and prior to getting our current Dragonfly 32 trimaran, I owned a Corsair Sprint 750 trimaran that we raced and daysailed on Lake Pontchartrain and all along the Gulf coast. The boat was stored mast up 99% of its life with me and I owned it from late 2006 to October 2022 so nearly 16 years. We switched to our first set of Dux standing rigging from Colligo in 2008. John Franta at Colligo was fantastic to work with and he knew how we stored the boat. That was early days for Dux and John thought that a reasonable life expectancy was 3 years so I followed his recommendations. I sent my old rigging back to him when I replaced it and he tested it and it still had over 75% of its failure strength and at that level still a very conservative safety factor. It was also economical to replace the rigging at that time (less than $500 for shrouds and a forestay). Since then, John has developed some coverings for additional UV protection so recommended lifespans are longer.

I have also been an active A-Class catamaran sailor since 2001 and I currently sail the foiling version of these incredible boats. I use both Dyneema forestays and shrouds and we tension our rigs pretty high. I’ve never had a failure and I’ve only seen one failure in over 12-13 years since I’ve seen A-Class sailors using Dyneema products for standing rigging.

The applications are certainly different for offshore racers and cruisers but I think the main challenge is to properly address chafe. Our 2016 Dragonfly 32 has all Dyform standing rigging (except the forestay) including the mast jumpers and diamonds. We will be due to replace this rigging in 4 years and I’m pretty sure we will use Dux for the two shrouds and go back with Dyform on the jumpers and diamonds. We’ve also replaced some wire rope systems with Dyneema on this boat.

I think when applied properly, it can be a very reliable option.