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Relative amounts of creep #161713
12/02/08 12:51 PM
12/02/08 12:51 PM
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Michigan
PTP Offline OP
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making a screecher and it has a luff pocket meant for wire but of course I am going to use line... and I have a question
which one of these has the least amount of creep?

amsteel blue (dyneema sk-75, not "standard" spectra)
vectran
AS-78
technora (tech 12, ultratech, T-900)

No one seems to quantify creep (they quantify stretch but it is not the same)
the amsteel is probably out due to high creep but thought I would throw it in there for discussion.

Secondly- if you pull the creep out- relatively easy to do- especially if it is tensioned like a halyard, does the line recoil when the tension is removed? I guess that would be stretch though... so then, theoretically if you get the creep out then it is out for good?

Last edited by PTP; 12/02/08 12:51 PM.
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Re: Relative amounts of creep [Re: PTP] #161733
12/02/08 04:02 PM
12/02/08 04:02 PM
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Originally Posted by PTP
if you get the creep out then it is out for good?


There's a joke in there somewhere....I just can't find it. grin


If your havin girl problems i feel bad for you son
I got 99 problems but my beautiful wife ain't one
Re: Relative amounts of creep [Re: ksurfer2] #161734
12/02/08 04:05 PM
12/02/08 04:05 PM
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Eastern NC, USA
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tshan Offline
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What is the old saying?? "You can take the boy out of the creep, but you can't take the creep out of the boy...."

Something like that.....


Tom
Re: Relative amounts of creep [Re: ksurfer2] #161737
12/02/08 04:44 PM
12/02/08 04:44 PM
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Jake Offline
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Originally Posted by ksurfer2
Originally Posted by PTP
if you get the creep out then it is out for good?


There's a joke in there somewhere....I just can't find it. grin


Creep has a logarithmic relationship with time and loading. For all practical purposes, after a certain period of time, it does effectively go away when considering steel or synthetic rigging. You will be plagued with a good bit of creep early in the life of the rigging. It will not be of much concern some time later. Steel creeps much less than synthetic rigging but it does creep and stop.

Creep (particularly in steel structures) can be beneficial by allowing highly localized (pin point) pressure areas to "creep" and deform slightly, without failure, to help distribute the high loading over a larger area.


Jake Kohl
Re: Relative amounts of creep [Re: PTP] #161739
12/02/08 05:09 PM
12/02/08 05:09 PM
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Hi PTP,

from my expierence with synthetic shrouds (sk75), I think initial creep is about 5%. I used them for half a year (mast up all the time), in the hope that the creep settles. However it found the shrouds to elastic in strong winds and got tired to retension the shrouds so often. In this time it doesn't settle.
I think that one part of the creep comes from the braid and will affect any braided line. But it should settle after first use. In addition to that some materials like dyneema creep.

Creep does not recoil, by definition.

Actually I don't know about AS-78 and technora, but vectran was designed to have "no" creep (rumors say as towing line for sonars). You need about three times the diameter as the wire to get the same stiffness, if I remember right.

Not sure how your sail is rigged. Is a screacher a flat cut genaker or suoer sized jib? Normally you have the luff line attached to the head and tack shackles of the sail. In this case, the creep of the line means that the luff of your sail has to carry more load (the luff keeps its original length, the line gets longer). Then, increasing the halyard tension stretches the luff more than the line, which might be mean to your sail... However on land you can shorten the length of the line from time to time.

I am a lazy guy and resetting some line in sails keeps me from sailing. I would take a "non creep" line. Like polyester or vectran if you want to save 100g or so for some $$$ more.

Actually I have a "hooter" or screacher or whatever (a flat genaker...) and I use polyester as luff line.

Hope that helps.

Cheers,

Klaus

Re: Relative amounts of creep [Re: Jake] #161740
12/02/08 05:16 PM
12/02/08 05:16 PM
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Hi Jake,

creep is permanent deformation even under low loads. "Plastification" is the permanent deformation under very high loads (e.g. your steel example). I know that some people says that dyneema creeps only under high loads, but my expierence with (high quality) ropes of sk75 is a different one. Creep is a killer for the trim of your standing rigging. At least my feeling about it.

Cheers,

Klaus

Re: Relative amounts of creep [Re: Smiths_Cat] #161764
12/02/08 08:41 PM
12/02/08 08:41 PM
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yeah, basically a large genoa actually.
You hit on the problem precisely. The line has to be "crept" until it reaches the length of the luff of the sail so I am not tearing the new sail in half. I have heard of people tugging on the synthetic line with their car/truck to get some of the creep out. Wonder if a truck could break a 5k breaking load line (slowly of course, sure it could with a jerk)?

Re: Relative amounts of creep [Re: PTP] #161778
12/03/08 05:10 AM
12/03/08 05:10 AM
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Brisveagas
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"What ever makes you happy... What ever you want.."

Dude you have to tell us what sort of boat you're putting it on. And im aware of the fact that its probably a Cat. The loads on the luff of an off the beach cat screecher would not be high enough to worry about creep in either poly or spectra or vectran.

Make it adjustable and you wont have to worry about it. Or get a qualified sailmaker to do it.

"i wish i was special.... your so f---ing special..."


Aido
Viper 288
Re: Relative amounts of creep [Re: PTP] #161789
12/03/08 09:39 AM
12/03/08 09:39 AM
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There' been entire volumes written onthis subject, but I'll try to summarize it.

It all depends on the size and loading percentage of breaking strength. If you're trying to maintain minimum diameter then wire is the way to go. If you're trying to save weight synthetic is the route.

Amsteel (sk75) is not appropriate for a luff wire unless you have a way to retension it - too much creep

Vectran has low creep, but has very low chafe and UV resistance - good for halyards, but not good for running or standing rigging.

AS-78 is an improved version of SK75, has excellent chafe and UV resistance, but still exhibits creep when loading at 60%+ of breaking strength.

Technora has low creep characteristics but absorbs moisture causing the fibers to swell. Once the fibers start swelling, it creates internal chafe within the braid and starts breaking down. You won't see it until the rope breaks, and it looks hollow on the inside.

There's a relatively new product out - Dynex Dux 75. They take SK75, heat and draw it through a die process. It realigns the chrystalyne (sp?) structure resulting in it being 40% stronger than SK75 and only having 3% creep at 90% load. 7mm Dux 75 weighs only 3.4 kg per 100 meters, and has a breaking strength 15,000 lbs.

Its pretty cool stuff, I've seen it used on ORMA 60's and Volvo 70's for standing rigging, strops, etc. I've used it to create backstays, inner forestays, and halyards for big monos.

Currently, I'm in the process of replacing all of the standing rigging on a R33 to reduce the weight aloft.

Re: Relative amounts of creep [Re: mikekrantz] #161796
12/03/08 11:21 AM
12/03/08 11:21 AM
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I20RI Offline
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I use dynex Dux for the standing riggin on my S 23 and it has 0 creep. I have spliced it many times making rigging for big monos and put it on a test bench to pull out the slack in my splice and can definitively say it has no creep whatsoever. It is heat treated and annealed under load, which makes it really stiff (maybe not the best trait for a leach cord.) It is also expensive. Regular dyneema or Vectran has almost no creep, but Vectran is UV sensitive and should be covered or painted with rope paint. If it is a luff or leach cord it should be fine since it is out of the sun. DUx seems like overkill for this application. I'd go with vectran. Amsteel creeps too much and technora is relatively stretchy (and a pain in the butt to work with)

Re: Relative amounts of creep [Re: I20RI] #161811
12/03/08 01:51 PM
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Small diameter vectran will fit your bill. Most vectran now has a coating for uv resistance but that is not an issue as it will be in the luff of the sail. As for abrasion vectran is strong in this department so no worrys there. I can tell you that pulling with small high tech line is interesting. I work at a car dealership and upon receiving a package from APS containing 5/32's vectran line and commenting on the breaking strength of the line I was told I was full of it. Money was wagered and we picked up the front end of a wrecked pickup truck by looping the line under the truck and then tieing it to the arms of a vehicle lift. The dry weight of a silverado is 4780lbs and we only picked up half the vehicle, but it was the heavy half with the engine.


Collin Casey
Infusion Platform + C2 rig and rags = one fast cookie
Re: Relative amounts of creep [Re: I20RI] #161819
12/03/08 02:50 PM
12/03/08 02:50 PM
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Like Mike said Dynex Dux definetly still has creep. Lots of people claim it doesn't but in practice it does. Doesn't mean its not cool tho.

A double braid polyester luff line would be fine in the luff of a screacher for a small boat. Cheap and you wouldn't put enough load on it to stress it out too much.

How big is the Boat PTP?


Aido
Viper 288
Re: Relative amounts of creep [Re: Aido] #161821
12/03/08 02:53 PM
12/03/08 02:53 PM
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Jake Offline
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I think he's talking about an F31.


Jake Kohl
Re: Relative amounts of creep [Re: Jake] #161826
12/03/08 03:05 PM
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Creep probably is an issue then. Any of the three or four PTP mentioned will do. Like i said it has to be adjustable. If its not you'll rip the sail in half. If you dont know what your doing you'll probably rip the sail in half any way.

Anti torque rope is what i would use so it can be furled and handled easily. It has relatively low creep too.

Who would've guessed a tri sailor on Catsailor.


Aido
Viper 288
Re: Relative amounts of creep [Re: Aido] #161828
12/03/08 03:25 PM
12/03/08 03:25 PM
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Originally Posted by Aido


Anti torque rope is what i would use so it can be furled and handled easily. It has relatively low creep too.

Who would've guessed a tri sailor on Catsailor.


I have a cat too.
Dynex would be ideal but the smallest size it comes in is 9/32 which is too big, IMO, for the luff. My tri has 9mm dux shrouds which do exhibit some creep when it is setting (although hard to determine, more likely the splices settling than overt creep).

What do you mean by anti-torque rope?

Re: Relative amounts of creep [Re: PTP] #161842
12/03/08 04:14 PM
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I don't remember if it is layline or APS but one of them I seem to recall offeres prestretching line, would that have the same effect at reducing creep? If so I might employee them to deal with my neighbor, talk about creeps.


Collin Casey
Infusion Platform + C2 rig and rags = one fast cookie

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