Dux rigging and Forestay Tesnsion

[Brian Duff]

Ok,
So we all know Dux creeps. This means that any tune you put on it will evenetually 'bleed off' to slack.

How then , do you propose to keep forestay tension? I have always set up the rigs with either an adjustable backstay (or runners on frac rigged boats) or with foiless headstays that use halyard tension to set luff sag.

Who has thoughts or experience on this issue?

[Brion Toss]

Hi Brian,
I think you are begging the question here. As I understand it, creep only occurs when the relative load is more than 20% of break strength. Therefore it is important to size any consistently loaded stay so that it never sees 20% of break. Undersize forestays will creep.
Forestays are one of our frequent Dynex pieces, because their ease of stowage is really compelling to owners. In my experience, once you get rid of constructional stretch -- which does take some effort -- you can put a good tune on and not get creep. Because the relative strength is so high, you can tune to lower relative loads than with wire.
So how is the South?
Fair leads,
Brion

[Brian Duff]

Boat sales is going pretty well, but I just miss rigging so much I find myself always talking with folks about it. Thats where i got this one from.

Are you saying that you have found, as long as the loads are 20% of break or less, actual working loads, that NO CREEP is noticed? I didn't find that with the rigs I had a chance to do before leaving... And want to sort it before doing my boat becasue I want to do a swept spreader no backstay set up.

I have always used stainless for the forestays, but have seen on this boat that the sidestays are swept aft (catamaran) and meant to hold forestay tension, but don't seem to. The kit is quite new, two weeks old, so maybe now that the constructional stretch is completely out they can tune the rig and be good, with no tuning required from here on out? That was not the case on the boats I played with, they accepted slack leeward rigging OR frequent tightening of rigging...

?

[Gashmore]

Dynex Dux being a plastic it will creep some under any load but it can be controlled if properly sized. My 8 month testing of some 9mm seems to indicate that creep is insignificant below about 7-8% of MBL and starts to get out of hand around 14-15%. One odd result that I don't fully understand is that repeatedly cycling from 6% to 15% of MBL didn't increase the creep rate much over the static 6%. The test was 300 cycle of 45 minutes at 1500 pounds and 15 minutes at 4000 pounds. Theoretically the creep should have been a lot more than was measured.

If you can keep the pretension under 10% a turnbuckle should give enough adjustment for several years.

[jfranta]

Originally Posted by Brian Duff

Are you saying that you have found, as long as the loads are 20% of break or less, actual working loads, that NO CREEP is noticed? I didn't find that with the rigs I had a chance to do before leaving... And want to sort it before doing my boat becasue I want to do a swept spreader no backstay set up.


?

Use the creep tables on our website for setting the line size for creep. We have not seen any creep issues when referencing the creep tables to set the line size for no more than about 0.5 inches per year based on expected pretension. We have published numbers for ceep for sizes up to 13 mm but have in house numbers for line up to 23mm diameter. We also size for desired stretch. This is one of the differences from steel, stretch and/or creep are the limiting factors with polyethylene line so we need to design for them. Creep is relatively easy to design around but demands a little more understanding than when using wire. When sized correctly for Stretch and Creep Dux strength is usually at least 2-5 times stronger than 1x19 in the same application, so strength is the secondary (or tertiary) consideration. We can help anyone to size their line just send us an email.

If you want to do a backstayless rig we need to understand the pre-tension that you will need to size correctly as it will be relatively high.


John Franta, Colligo Marine.

[Mark Johnson]

#637
Mark Johnson
Registered User





Join Date: Sep 2009
Location: New Bern NC
Boat: Searunner 34 "Delphys"

Posts: 81
Replacing SS standing rigging with Dux?

--------------------------------------------------------------------------------

I need some feedback... You especially could help Jack.
I am considering using Dux rigging for my running backs for starters, but have a couple of reservations. One is the lifespan. They claim 5 years, as compaired to 8 for 316 SS. This confuses me... As a boatbuilder/cruiser, I don't have many racing friends, or for that matter friends with million dollar mega yachts. But none of the thousands of people I have known over 40 years of doing this, has changed out their SS rig @ 8 years old, just because! Mine, (316 1X19 wire), is 14 years old, and technically due for replacement, yet it looks perfect. (I use properly installed Sta Locs). In all of these years, and tens of thousands of miles, I have re-tuned only once. (almost no creep) In fact, as I replace my wires, I'd gladly have them destruction tested, and bet $1,000 that they would test out at 90% of their origional strength. At least I'd do it once. I can't afford to be wrong more than that!

With synthetics exposed to UVs, If & when it is determined that 5 years is the safe replacement interval, that's when I'd replace it! So this issue of having from half to one third the lifespan, makes the Dux look quite expensive by comparison to SS. Time will tell?

I have re-read Jack Molan's impressive volume of information on Dux and gather that replacing my too stretchy 1/4" wires with 7MM Dux would result in "creep" that would require regular Re-tuneing. However if I go with 9MM, I have VASTLY more strength at less stretch, and almost no "creep" issues. This is a plus, so I'd oversize to minimize "creep".

Also I see that there is a UV cover available with slightly more windage. (double the lifespan)? I assume that the splice over the terminator is left bare? Is this the case? If so, is it assumed that the line being thicker at the splice/terminator, makes it enough stronger here that the UVs don't make this area the stay's weak link.

Then there is windage... I know that due to the vortices created, things like a wire have far more wind resistance than their windage alone would indicate. This creates parasitic drag. (especially with our 12 wires) Has it been determined that the undeniably "lighter on her feet" motion of a lighter rig, is a bigger plus than a rig with less windage. I would assume that a fatter but way lighter rig wins out, but wonder if it is a fact?

Then there is one more concern. The terminators being of aluminum, and attched to the SS mast fork tangs by a SS clevis pin, (with the cheeks chaffing the anodizing), or my runner's SS pin attched snapshackle, makes for a corrosion potential. This may be purely cosmetic, or it may eat away enough material to make the terminators expendable, just like the line, in 5 or 6 years. (even more expensive)

Don't get me wrong. I like the idea of using Dux. I plan to give it a try on my runners... I hope this stuff really is a viable alternative to conventional SS wire. I know I need a less stretchy alternative to what I have. (1/4" 316 1X19 SS wire) I just have these reservations, and this is too new a technology to have a proven track record, at least as far as a replacement for a sailboat's standing rigging. (at a similar cost over time?)

Any feedback on the subject would be appreciated...
Mark J

[Mark Johnson]

Mark Johnson
Junior Member Join Date: Oct 2010
Location: New Bern NC
Posts: 3

Rephraising the question...

--------------------------------------------------------------------------------

I found the answer to some of my question... (at the bottom). This leaves me with one final question about using Compact Strand Wire.

I see that the Issue of UN screwing my StaLocs is moot, because it will actually tighten them as the wire tries to unlay..

If I have no hydraulic back stay, but have only cottered turnbuckles, I could install the wires with half a twist of "pre spin" on them, and presumably the turnbuckles cotter pins can easily resist the wire from unlaying and spinning the turnbuckle. Is this correct?
Is the tendency to unlay enough to overcome the cotter pins?

I don't want to have my turnbuckles making half a spin of turn when the rig is loaded up, only to return when it's not. The return spin could unscrew my Sta Locs.
Will the above method of installing the wire with half a turn of tightening pre spin, keep my turnbuckles firmly against their spin restricting cotter pins, and stay there, even under load & a trimarans more active motion at sea?

Thanks! Mark Johnson



Technical Notice - Dyform™ Wire with Hydraulic Cylinders

Unidirectional lay wire (such as Dyform™, or “compacted strand”) is used in rigging applications where designers desire a lower-stretch solution than standard 1x19 wire rigging. Several problems result from the use of this wire with hydraulic cylinders including lower effective stiffness, unwinding of the lay of the wire and unscrewing of the rigging fitting assemblies.

Dyform wire is twisted in only the left hand direction. This construction improves the strength and stiffness of the wire when compared to 1/19 wire of a similar diameter. However, Dyform tries to “unwind” as it is loaded due to this construction. Hydraulic cylinders have no provisions to prevent this unwinding rotation. As the Dyform unwinds, it grows longer and the stiffness is effectively reduced. When the load is removed, hydraulic cylinders may not allow the wire to fully re-wind. After several loading cycles, the Dyform wire may be significantly unwound. The residual torque from this condition can act to unscrew rigging fittings on the wire. Based on the points above, Navtec does not encourage the use of Dyform wire with hydraulic cylinders.

Dyform is generally recommended for use with the appropriate swaged and swageless fittings without hydraulic cylinders. Swaged end fittings prevent the unwinding by locking the wire. During loading, right hand threads, such as those in swageless end fittings are tightened by the unwinding of the wire and are not affected. When unloaded, the wire fully re-winds and there is no residual torque to unscrew the fitting. Of course, as is the case with all rigging assemblies, it is important that all threads be locked.

For boats that have Dyform with hydraulic cylinders installed there are several alternatives. One alternative is to replace the Dyform with the equivalent 1 x 19 wire, rod or Kevlar cable.

The other alternative is to continue to use the Dyform wire with the hydraulic cylinder. In this case, it is very important to be sure that the threaded fittings in the stay are reliably locked against rotation. Since there is no thread in a swage eye, the swage eye does not require extra measures for locking it. Of course, the threaded joint(s) in a swage stud or swage turnbuckle assembly require locking.
While Loctite is frequently used with good results, due to possible variations in application, we do not recommend Loctite alone as an adequate lock in this case.
Acceptable locking methods include:

1. Adequately sized cotter pins such as are used in locking turnbuckles.
2. “Dinging” such as has been used to lock noses in marine eyes and other such assemblies. This requires the use of a dinging press, which can be found at many Navtec rigging shops.
3. Set screws. The set screw must engage a recess in the inner (male thread) surface and the set screw must be locked against loosening by Loctite.If the decision is made to use Dyform wire with a hydraulic cylinder, as with all rigging, it should be regularly checked for signs of deterioration. Signs of excessive unwinding of the lay may include broken strands, kinks of the wire or strands, or significant unevenness of the lay or construction. In practice, we have not observed these effects and think they are unlikely.


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[Brion Toss]

[quote=Mark Johnson;5430]#637


I need some feedback... You especially could help Jack.
I am considering using Dux rigging for my running backs for starters, but have a couple of reservations. One is the lifespan. They claim 5 years, as compaired to 8 for 316 SS. This confuses me... As a boatbuilder/cruiser, I don't have many racing friends, or for that matter friends with million dollar mega yachts. But none of the thousands of people I have known over 40 years of doing this, has changed out their SS rig @ 8 years old, just because! Mine, (316 1X19 wire), is 14 years old, and technically due for replacement, yet it looks perfect.[/html]

First, the 5-year number is arbitrary, and deeply conservative (unlike the 8-year number for wire, but more on that in a moment). Actual testing in tropical conditions shows Dynex, at least, being in better relative shape than stainless in the same conditions. Some forms of Spectra are less UV-resistant than Dynex; that and the engineering tendency to err on the conservative side with new stuff accounts for the 5 number. In Northern climates, the lifespan of Spectra is much, much longer.
8 years, on the other hand, is a good number for stainless in the tropics, and this is based on many years of experience. Older than that, and the effects of fatigue, chloride corrosion, and crevice corrosion tend to result in wire failures. Yes, hardly anybody replaces their rigging after 8 years, even in the tropics, but it's a good recommendation. Again, in the North, with lower temperatures, lower salinity, and often lower average windspeed and boat usage, wire can last much longer; here in the Northwest, a rig can be in fair condition after up to 20 years, for example.

(I use properly installed Sta Locs).

Probably not, if you followed Sta-Lok's instructions. They specify too little of the wrong kind of sealant. Corrosion can kill "properly installed Sta-Lok's."

In all of these years, and tens of thousands of miles, I have re-tuned only once. (almost no creep) In fact, as I replace my wires, I'd gladly have them destruction tested, and bet $1,000 that they would test out at 90% of their origional strength. At least I'd do it once. I can't afford to be wrong more than that!

You'd probably win that bet. In fact, if the wires have lived North, you might find that their break numbers exceeded 100%, as stainless gets stronger (work-hardens) as it cycles. The problem is that it also gets more brittle, leading to sudden failures. Young wire is reliable wire. Oh, and regarding the "almost no creep" reference, actually you have had absolutely no creep; creep is not a characteristic of steel. If you had to retune, it was because your hull had deformed, or you moved to a higher windspeed area, or your hull loading changed, or, gods forbid, you exceeded the wire's elastic limit.

With synthetics exposed to UVs, If & when it is determined that 5 years is the safe replacement interval, that's when I'd replace it! So this issue of having from half to one third the lifespan, makes the Dux look quite expensive by comparison to SS. Time will tell?

Time has told, and Dux appears to hold up at least as well as stainless at a given level of safety.

I have re-read Jack Molan's impressive volume of information on Dux and gather that replacing my too stretchy 1/4" wires with 7MM Dux would result in "creep" that would require regular Re-tuneing. However if I go with 9MM, I have VASTLY more strength at less stretch, and almost no "creep" issues. This is a plus, so I'd oversize to minimize "creep".

It depends. Creep is time-dependent, so for your runners, you might not leave them up long enough (100 hours or so) for the effect to occur.

Also I see that there is a UV cover available with slightly more windage. (double the lifespan)?

Covered Spectra is basically immortal.

I assume that the splice over the terminator is left bare? Is this the case? If so, is it assumed that the line being thicker at the splice/terminator, makes it enough stronger here that the UVs don't make this area the stay's weak link.

Think this through. All the extra mass is inside the rope, and it is held in place by the outside. We serve the portions we can't get the cover over.

Then there is windage... I know that due to the vortices created, things like a wire have far more wind resistance than their windage alone would indicate. This creates parasitic drag. (especially with our 12 wires) Has it been determined that the undeniably "lighter on her feet" motion of a lighter rig, is a bigger plus than a rig with less windage. I would assume that a fatter but way lighter rig wins out, but wonder if it is a fact?

I don't have numbers for this, but my experience says yes, lightness winds out over windage, at least at this scale.

Then there is one more concern. The terminators being of aluminum, and attched to the SS mast fork tangs by a SS clevis pin, (with the cheeks chaffing the anodizing), or my runner's SS pin attched snapshackle, makes for a corrosion potential. This may be purely cosmetic, or it may eat away enough material to make the terminators expendable, just like the line, in 5 or 6 years. (even more expensive)

A little Tef-Gel where the tangs meet the terminals will prevent corrosion. The pin holes are bushed with a non-reactive material. Don't use thimbles, or snapshackles, on your runners.

Fair leads,
Brion Toss

[Brion Toss]

Originally Posted by jfranta

Use the creep tables on our website for setting the line size for creep. We have not seen any creep issues when referencing the creep tables to set the line size for no more than about 0.5 inches per year based on expected pretension.


John Franta, Colligo Marine.

Hi John,
Just a note to say that, as you and I have discussed some, tuning for Spectra should be much, much lower than with wire. The reason is that tuning is largely a matter of dealing with anticipated dynamic stretch; you need, for instance, to pretune uppers at up to 20% of break, with wire. But Spectra, properly sized, is far stronger, relative to the load, so can have much less pretension. That makes it vulnerable to creep only when under way, which is a small percentage of its life, even in heavily sailed boats. Once we stopped tuning like wire, creep dropped off immensely.
Fair leads,
Brion

[Brian Duff]

Brion,

WE are also finding here that the pretension is not needed. IT seems that even though the lee rigging is a bit slacker when sailing, we still don't get any 'bouncing ' like I have felt with wire rigs....