Issues with synthetic rigging?

[Mark Johnson]

Can any of you guys with years of experience using synthetic rigging, fill me in on the following?

The comparison that I would like to see between Dux and 316 SS wire, is @ 18 or 20 years old. Of the countless thousands of boats in our area, (Eastern NC), there has only been one dismasting in the last 5 years to my knowledge, and it was a new racing boat under extreem conditions. If one removes from the conversation the < 5% who are cruising all over the world, or live full time in the tropics... The other 95% around here spend winters in the Bahamas, are daysailors & local cruisers, or make a couple of one or two year Caribbean cruises... still spending the majority of their years in our moderate lattitudes, and brackish water. Of this 95% of cruisers, almost all go over 18 or 20 years before changing out their rigging, some even go to 30 years, (admittedly at their own risk)! Has your accelerated UV testing made a compairison to wire at this 18 + year life span, under the above circumstances?

Another point I am curious about... I have switched to some DUX synthetic rigging 6 months back, they are for my running backstays, and DUX seems like a perfect application here. I normally leave them "made up" and fairly snug, to use as a handhold when boarding the boat. When using the staysail, I will put 4 more turns on the "quick adjust" handle turnbuckles, but so far, haven't given them the acid test.
I go to the boat daily, and have noticed that @ 75 degrees F, the runners are quite snug, but @ 40 degrees F, perhaps that same morning, they hang completely limp. Since solid materials expand when heated, and contract when cooled, it can't be that the DUX has gotten longer on a cool morning. I assume that the metal mast has contracted at a rate vastly higher than the DUX, creating loose runners in the morning. Presumably with wooden or composite spars this is less of a problem,. My wire rigging has never done this "changing tune with temperature", and I imagine that it's because the wire expands and contracts at a rate somewhat similar to the metal mast.

With aluminum mast that are long & skinny, (like mine), and dependant on consistant shroud tension to keep the mast in column, wouldn't this become a problem if I tune the rig in the summer, then go sailing on a cool fall day? Has anyone else noticed this characteristic? I have done a LOT of reading on synthetics, and have yet to see this subject brought up...

Best regards, Mark

[benz]

Hi Mark,

I´m only at about 18 months with my Vectran rigging, but I too have observed the tune to vary with temperature, as have other sailors I´ve spoken to with aluminum sticks/Dux rigging. Less of a concern with my gaff-headed rig, since all my shrouds are less tight than a bermudian´s, but I´d also really like to know. Perhaps Mr Franta of Colligo will chip in soon.

[Chorine]

Poly aramids (Kevlar, Vectran) have a negative coefficient of thermal expansion. I wonder if this applies to the Dynex type materials? If so then the rigging would actually be getting longer in the cold as the mast gets shorter.

[John Stone]

Mark,
I too live in Eastern NC and we do get wild temperature swings in a single day. Your question about how temperature affects the dux is interesting and I would sure like to hear more about it from the professionals. I have zero experience with dux but have been reading a lot about it and am very much considering rerigging my 36' cutter with it. I have heard from a sailor that rerigged his 35' yawl with dux about 18 months ago. He had a lot of good things to say about the dux but he also mentioned the same thing about temperature changes affecting the dux tension. He said it was annoying. Overall, I think he is very pleased with it.

[jfranta]

Originally Posted by Mark Johnson

Can any of you guys with years of experience using synthetic rigging, fill me in on the following?

The comparison that I would like to see between Dux and 316 SS wire, is @ 18 or 20 years old. Of the countless thousands of boats in our area, (Eastern NC), there has only been one dismasting in the last 5 years to my knowledge, and it was a new racing boat under extreem conditions. If one removes from the conversation the < 5% who are cruising all over the world, or live full time in the tropics... The other 95% around here spend winters in the Bahamas, are daysailors & local cruisers, or make a couple of one or two year Caribbean cruises... still spending the majority of their years in our moderate lattitudes, and brackish water. Of this 95% of cruisers, almost all go over 18 or 20 years before changing out their rigging, some even go to 30 years, (admittedly at their own risk)! Has your accelerated UV testing made a compairison to wire at this 18 + year life span, under the above circumstances?

Another point I am curious about... I have switched to some DUX synthetic rigging 6 months back, they are for my running backstays, and DUX seems like a perfect application here. I normally leave them "made up" and fairly snug, to use as a handhold when boarding the boat. When using the staysail, I will put 4 more turns on the "quick adjust" handle turnbuckles, but so far, haven't given them the acid test.
I go to the boat daily, and have noticed that @ 75 degrees F, the runners are quite snug, but @ 40 degrees F, perhaps that same morning, they hang completely limp. Since solid materials expand when heated, and contract when cooled, it can't be that the DUX has gotten longer on a cool morning. I assume that the metal mast has contracted at a rate vastly higher than the DUX, creating loose runners in the morning. Presumably with wooden or composite spars this is less of a problem,. My wire rigging has never done this "changing tune with temperature", and I imagine that it's because the wire expands and contracts at a rate somewhat similar to the metal mast.

With aluminum mast that are long & skinny, (like mine), and dependant on consistant shroud tension to keep the mast in column, wouldn't this become a problem if I tune the rig in the summer, then go sailing on a cool fall day? Has anyone else noticed this characteristic? I have done a LOT of reading on synthetics, and have yet to see this subject brought up...

Best regards, Mark

Hi Mark, please see the FAQ's on our site about Colligo Dux Rigging.
We now have enough data to say 5-8 years for a replacement interval of Dynex Dux in the Tropics. This data is still coming in and we are watching it closely. As an engineer and a sailor, I can tell you that I wouldn't feel comfortable going offshore with a stainless rig on a saltwater boat over 10 years old unless, possibly, I knew it was washed with freshwater almost daily. Maybe with stayloks that were completely inspected, certainly not swage fittings. To my knowledge, most of the wire rope manufacturers recommend 8-10 years as a replacement interval for stainless wire. I am sure Brion has a valuable opinion here.

On the tuning, 2 things.

1. The coeficient of thermal expansion (COTE) of dyneema is less than that of aluminum, so you get a difference in expansion rates in the temperature ranges you see on a boat. If you do some calcs on an aluminum mast you would probably be surprised on how much growth you can expect. The COTE of Steel is also different than aluminum but not as much and is usually masked by the higher amount of pretension with turnbuckles.

If you use turnbuckles with some amount of pretension you will usually not see the loosening of the shrouds, if you use lashings than you will probably notice it as the amount of pretension will probably not be enough to cover the thermal expansion of the mast. Some of our customers have noticed this and after tensioning in colder weather they have enough pretension to not see the issue again. If you have a rig that requires more pretension (or better control of tension) we recommend using turnbuckles for pre-tensioning.

We also now have Loos gauge calibrations for several sizes of Dux to help with setting the tension.

You will have a little more maintenance with Colligo Dux, especially with lashing tensioners, but you should expect this as you need to inspect for chafe more (than steel) also. All synthetics, PBO, Carbon, Dyneema, Aramids, etc put more responsiblity in the hands of the sailor as there are alot of unknowns as none of them have been used as long as Steel.

You will not find a synthetic rig that will give you the same amount of confidence as steel for probably about another 100 years or so.

John Franta, Colligo Marine

[Brion Toss]

Hello all,
We are in the process of returning to a world where sailors are a living part of their rigs, responsible for design and fabrication, as well as maintenance and use. Part of that process requires familiarizing ourselves with the assorted materials, and the interactions thereof. The expansion issue being discussed here is a piece of that.
As John notes, the pretension required for a (proper) tune with wire masks differences in expansion rates for aluminum and steel. But if you put a tension gauge on the wire on a cold day, and then a warm one, I think you'll be surprised at the difference. In the Northwest, we can use this to our advantage, as the colder days usually have higher windspeeds.
With Spectra, very little pretension is normally needed, so there's less "travel" needed for the rigging to go slack. This might mean more frequent or seasonal adjustment, and it might mean finding an average pretension -- under the "creep" level -- to tune to.
As for longevity, it looks like uncovered Spectra will last at least as long, safely, as stainless in the same climate. Covered Spectra, which costs about 40% more and is more difficult to splice, might still end up being long-term cheaper, as it will basically be immortal. That's why I'm recommending it to cruisers who expect to be in the Tropics for any length of time. Might make a difference in resale value, too. And even with the extra cover weight, it's still lighter than wire.
Fair leads,
Brion Toss

[Mark Johnson]

Hi Brian,
Your explanation about my Dux runners "seeming" to have a larger temperature induced expansion differential than the wire ones did, being partly because, unlike the rest of the rig, I had them snug, but with no pre tension, makes good sense.

The thing is... when my runners were wire, I had the exact same practice of having them rigged up "just" snug as a hand hold, and putting 4 or 5 turns on them for the rare occasions that I needed my staysail. (I have folding handle, "quick adjust" turnbuckles on the runners).

When I had the previous wire runners, and there was a difference between morning temps, to 35 degrees hotter that afternoon, the difference in wire tension was small enough that I couldn't tell without using a tension gauge. I never noticed it at all in fact. With the Dux, starting with the exact same tune, they hang completely loose in the morning, with some slack as well, and that afternoon, if it is 35 degrees hotter, they would be REALLY tight! (So much so, that to oppose my staysail stay, I might only put one more turn on them! The difference between the two materials behavior, at least in my admittedly limited observation, is pronounced!

It is of no consequence in my application, with such easily adjusted turnbuckles, and I think my runners is an ideal application for these lighter synthetics, but for the rest of the rig, I thought that this observation would be useful for others in deciding where they apply and where they don't... (like a short fat extrusion with all shrouds at similar pre load, VS a long skinny one with really tight uppers and fairly slack lowers. Just something to consider...

Mark

[steveR]

If the mast were composite............would there be any issues along these lines???

[echidna]

So let's look at some actual data for coefficients of linear expansion:

Aluminum 6061: 24E-6 per deg C
Stainless steel 316: 16E-6 per deg C
Dyneema: -12E-6 per deg C

I'm not sure how accurately the value I found for Dyneema applies to Dynex Dux, but I'll assume it does.

So, if for the sake of simplicity, we assume a shroud of equal length to an aluminum mast (as would be a good approximation for a deck-stepped, masthead rig), we have the following differential coefficients of linear expansion between mast and (cap) shrouds:

SS 316 rigging: 8E-6 per deg C
Dyneema rigging: 36E-6 per deg C

So the effect of differential expansion is 4.5 times greater for Dyneema in this case.

To get an idea of what this means with Dyneema/Aluminum, consider a variation in temperature from 0 to 30 deg C. This gives a relative length change of 30*36E-6 or 0.0011. Assuming all the elasticity is in the Dyneema (i.e., neglecting elasticity of the hull and mast), this corresponds to a change in load in the shroud of order 6% of breaking strength, based on the Colligo data. This value is probably greater than the pre-tension acceptable in terms of creep.

For comparison, with a SS 316 shroud, the change in load would be of order 2.5% of breaking strength, which should be compared with a typical pretension of say 15% of breaking strength for SS.

I worked these numbers quickly, so I’m open to correction on the math, but assuming it’s correct, the difference between Dyneema and SS is quite significant in this regard. Obviously I’ve made a number of simplifications in my model, but I think the general results will be reasonably valid.

[Brion Toss]

Hi,
And thanks for the numbers. I can see that this might be an issue, but would like to throw in some qualifiers. First, the range, in rational measure, is from freezing to 86 degrees. Not likely to happen in a day, or in a given season. Next, the 15% tension you give for stainless is typical for long wires, like uppers and jibstays. Next, it seems to all depend on what kind of pretension the Dux would be set at. If these numbers are accurate, one could have shrouds at about 6% when slackest, and 12% when tightest, which would keep it under the worst creep levels. In my climate, this varying tension works out for stainless, as the winds tend to be highest when temperatures drop, so this could actually be a feature.
Anyway, looking forward to further documentation and analysis. And to the adaptations we come up with in response.
Fair leads,
Brion Toss