Lets talk about rope....

Daimond

Super Anarchist
4,118
0
SF Bay Area
Talked to a local rigger/boat owner/racer and he told me that stretch or creep or elongation is not necessarly linear. If a line has .5% stretch @ 40% working load it could have .4% stretch @ 10% working load. He thinks that orientation of the core strands has a lot to do with it.

 

NED28

Member
@Christian: thanks for clearing that up!

@Savoir: Please do your homework before posting: Spectra and Dyneema are both HMPE fibers, Hence of the same family. Dyneema is made by DSM using their proces, Spectra is made by Honeywell (to my last account) on license using their own processes. They have different characteristics and are thus not the exact same fiber, although they share origins. This is similar to all the aramid-family fibers such as kevlar, technora, twaron etc..., same family, different characteristics, different fibers

Creep comparison Spectra vs Dyneema.jpg

 

dacapo

Super Anarchist
13,841
1,683
NY
madonna mia.............my head hertz

can't we all just go back to hemp :ph34r:
If you think your head hurts now, wait until you smoke some hemp...

How's the charity regatta coming along? I'll nudge Julien.

Cheers,

MikeR
:lol:

Charity regatta is moving along. NoR will be out next week, I have a local beer distributor already signed on to sponsor (I may have Capt. Morgan's rum soon too...)

I've got commitments from about 15 boats so far, but I'm sure that number will go up as soon as NoR is posted and registration forms/sponsor forms are all printed and distributed

 

Tucky

Super Anarchist
3,502
33
Maine
Creep is the PERMANENT plastic deformation (think clay or play dough)

Stretch is temporary elastic deformation (think rubber band)
Waaaay back in the day, when I was younger, folks used to take a plastic six-pack holder (the bird killer kind), fold it so all six rings were concentric, grab in two hands and try and pull apart. Strong folks could snap the rings in two, but for most the plastic would stretch and deform, going from milky to clear and gaining strength in the process. If it didn't snap quickly, even the strongest couldn't snap the clear stuff.

I think we were manufacturing UHMWPE or something, if only I'd known. I never could snap the stuff.

Always the experiment, never the control.

 

Weyalan

Super Anarchist
For what it is worth, I think that "creep", strictly speaking, refers to non-recoverable deformation resulting from cyclic loading where the load is relatively small in comparison to the yield strength of the material. Non recoverable (plastic) deformation is usually associated with loads up around the yield strength, but a load that, if static, wouldn't even begin to cause plastic deformation, can cause creep deformation if applied cyclically.

 
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savoir

Super Anarchist
4,914
201
Creep is the PERMANENT plastic deformation (think clay or play dough)

Stretch is temporary elastic deformation (think rubber band)
Waaaay back in the day, when I was younger, folks used to take a plastic six-pack holder (the bird killer kind), fold it so all six rings were concentric, grab in two hands and try and pull apart. Strong folks could snap the rings in two, but for most the plastic would stretch and deform, going from milky to clear and gaining strength in the process. If it didn't snap quickly, even the strongest couldn't snap the clear stuff.

I think we were manufacturing UHMWPE or something, if only I'd known. I never could snap the stuff.

Always the experiment, never the control.
You were right. Plastic six pack holders are made from Spectra.

 

Mikel_new

Member
208
6
Bilbao
100% agreed.

Yet nobody mentioned U/V.

PBO would just desintegrate in minutes (or thereabout) wothout a cover; vectran is a bit better, but should not be used without cover.

For most applications, dynnema is the most flexible and reliable fibre, in my opinion, except for standing rigging. Even AC-32 boats carried PBO halyards only on the real races, dynnema for training, etc.

Even the new 3Di sails use a lot of dynnema (plus Carbon) in the laminates, since they behave long term much better than aramids.

Couple of thoughts on the replies above

  • Creep vs Elongation: if I understand correctly: Creep is a function of time and load and reversible (when you take the load of there is no more creep), considering the race time (day of W/L races) and loads on typical 30-35 foot racers creep should be non-existent for most of us. Elongation is the irreversible lengthening of a strand of rope. this happens over a long period of time (probably unnoticable during a day's racing) and results in a permanently longer strand of rope. This is also why typical lines are pre-strectched at the factory. The numbers in the table I posted earlier refer to elongation.
  • Creep in halyards in first windward leg: maybe you've already tried or disproven this, but I have found on numerous occassions that if the halyard tension drops this has nothing to do with the halyard material, but with the quality/state of your stoppers. When we left the halyard on the winch there was no tension drop any longer (which has its own annoying side effects).
  • Vectran vs Spectra: Here in NL the typical store only has Polyester rope or Dyneema (and let me restate that Spectra is not the same as Dyneema), so I have never seen or touched Vectran and have no idea of the cost. But knowing how some people make buying decisions: Could it be that on the typical yacht people use Vectran rather then Spectra or Dyneema because of price? Same why we wouldn't (yet) buy SK90 for our round-the-cans racer but rather SK75 as the price difference is so much greater then the noticable added benefit to us
Few corrections:

Elongation is just another word for getting longer - can be either temporary (elactic) or permanent (plastic)

Creep is the PERMANENT plastic deformation (think clay or play dough)

Stretch is temporary elastic deformation (think rubber band)

Spectra and Dyneema are two different brand names of the same chemical rope material.

Vectran has about the same stretch as SK75 Dyneema and much less creep. It is price wise close. Dyneema has better UV and abrasion resistance. Choice of one vs the other obviously depends on the application. An example: My main halyard is a 2:1 Vectran with (at the working end) a Dyneema tip - this way I have the low creep Vectran but with the exposed parts running over the sheave and the main shackle (when hoisted or stored) in Dyneema. Works wonders. I had problems with a pure Dyneema halyard hence the switch.

SK-78 is getting close to Vectran in terms of Creep - but still not as good

SK-90 Don't know about creep as it hasn't been released but the expectation is that it is not better than SK-78 as the emphasis of SK-90 over SK-78 was breaking strength increase more than anything else. Would also expect a bit less stretch as it is really just a heat treated 78 (a'la DUX but done before braiding) - expect a bit more constructional stretch due to the construct.

At lease that is my $ 0.02
 

erdb

Anarchist
786
575
- initial "stretch" isn't stretch. It's the application of load to align a suboptimal structure. How much a length stretches depends on it's construction, to include the weave and splices. Maybe better called set-lengthening.
Great discussion, especially because I'm planning to replace the backstay on my 23' boat with ultrex. I was wondering how much initial stretch/set-lengthening should I calculate for a 30' piece of 3/16 line with two eye splices on the ends? While I don't have to match exactly the length of the original wire, I'd like to be reasonably close.

Another question - which eye splice would you recommend for this? Tail burried or brummel? I've read somewhere that brummel can reduce breaking strength as much as 40%. Is that true?

Thanks!

 

owlslick

Member
485
0
No one mentioned "modulus" data as a measurement of line / fiber characteristics. It may be a better value of a finished line characteristics vs the characteristic of the raw material used in a line / fiber and in it's final real world application.

Using high modulus line is a way of reducing stretch which goes to easier less demanding sail trim and...not chasing sail trim as the loads change improving the entire racing or cruising experience. It is not a "free lunch"going to higher modulus lines. The shock loads go up significantly which can lead to blown blocks and other stress related rig failures. In dingys that is not much of an issue, but increases as the size of the boat and loads go up. When upgrading lines to higher modulus lines, it is good review the load ranges of the various blocks etc to avoid any surprises. Low stretch is the sailors friend.

 
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Young's Modulus, or Elastic Modulus is the slope of the elastic portion of a materials stress-strain plot. I mentioned it from the start. It is exactly what I think is necessary for people to make intelligent informed decisions. I agree that published data should be of the finished product, and not of the material... however that would be a great start. There is much more information than breaking strength which goes into material choice.

I don't think the backstay length will change much, especially since its probably on a purchase that can be trimmed easily.

I do not believe that brummel splices reduce breaking strength any more than a non-locking splice. The tail gets buried whether the splice is locking or not.

 
very interesting and informative topic. What then to use as stays for an a-cat (leave the wires for the diamond out of the question) with low tension most of the time (it can more or less be rigged by hands). Can I use spectra/dyneema or shall I go for vectran/PBO?

Regards

Lars

 

erdb

Anarchist
786
575
I don't think the backstay length will change much, especially since its probably on a purchase that can be trimmed easily.

I do not believe that brummel splices reduce breaking strength any more than a non-locking splice. The tail gets buried whether the splice is locking or not.
Thanks, I decided to use the simple tail bury with long tail, long taper and lock stitched the hell out of it. I found conflicting info on the brummel. Some say it's just as strong as tail bury, others talk about 40% loss in strength. Maybe it depends on who makes the splice. Would be nice to see a test with the two types of splice on the ends of a line to see which breaks first.

 
I don't think the backstay length will change much, especially since its probably on a purchase that can be trimmed easily.

I do not believe that brummel splices reduce breaking strength any more than a non-locking splice. The tail gets buried whether the splice is locking or not.
Thanks, I decided to use the simple tail bury with long tail, long taper and lock stitched the hell out of it. I found conflicting info on the brummel. Some say it's just as strong as tail bury, others talk about 40% loss in strength. Maybe it depends on who makes the splice. Would be nice to see a test with the two types of splice on the ends of a line to see which breaks first.
The loss of strength in the Brummel splice does not come from the bury or lack thereof. The Brummel method locks the line and the line experiences loss of strength similar to a knot. The percentage of strength loss was all over the board. Some were around 20% some around 40 (hardly consistent). Regardless, sometimes Brummels are necessary when you're dealing with a line which is too short for a real single braid splice.

All of the chatter in this thread is great to read and wonderful know but on the water, I’ve seen guys using Vectran beating guys using PBO and guys using Spectra beating guys using Dyneema. All of that has nothing to do with charts or graphs and everything to do with going the right way.

 

sloansailing

Anarchist
855
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Anacortes
The loss of strength in the Brummel splice does not come from the bury or lack thereof. The Brummel method locks the line and the line experiences loss of strength similar to a knot. The percentage of strength loss was all over the board. Some were around 20% some around 40 (hardly consistent). Regardless, sometimes Brummels are necessary when you're dealing with a line which is too short for a real single braid splice.
My understanding is if the bury and taper are correct with a brummel it will be no less strong than a straight bury since the bury will hold the load and the "locking" function of the brummel will not point load the fibers. That said I don't like brummels either unless absolutely necessary. Where did the line break in your tests?

All of the chatter in this thread is great to read and wonderful know but on the water, I’ve seen guys using Vectran beating guys using PBO and guys using Spectra beating guys using Dyneema. All of that has nothing to do with charts or graphs and everything to do with going the right way.
+1

 
The best sailors will always win no matter what the equipment. For a lot of yachts and sailors, materials should simply come down to an economic question. However, in order to make an informed decision when the consumer wants to try and benefit from a materials advantage, you cannot avoid this subject.

Case in Point. I sail 505's. We often want to be able to use the best material for any given application so that our boat goes faster. A guy in the fleet decided that he needed a new forestay. The maximum rig tension used on the boats is 700 lbs at the dock, lets say a factor of 1.5 for sailing loads. So that means the most the boat would probably ever see while sailing is 1000 lbs in the sidestay. Convention tells us that loads in the forestay are about half of the sidestays. So, for his forestay, he needed a line with little stretch, good UV resistance, and light weight that operated at a maximum load of 500 lbs. I believe he ended up choosing 1/8" dyneema (sk 75). The tensile strength of the line is listed at 2,500 lbs.

Should be fine right? There is no way that line would ever get loaded enough to break while sailing. The "stretch characteristics" of sk-75 are 0.75% of elongation at 30% of the breaking strength. 500/2500 is 20%. To make the math easy, for a 20' forestay, he could expect 1.8" of stretch at maximum sailing loads, plus whatever length the splices set. Thats great! He made the forestay, put it on the boat and maxed out his rig tension for the morning to set the splices and remove "constructional stretch", calibrated the boat (i.e. had to know exactly how long the forestay was) and went sailing hoping to enjoy his upgraded material for evermore.

But thats not what happened. The conditions were light...call it 6 - 10 knots. At 12 kts of breeze, the boat is fully powered and just starting to plane. We don't like to crack the rig back before 12 kts of breeze. In the light, for some reason, his pointing got worse and worse. Then he noticed his boom was getting lower. Wait a minute! That's what happens when we rake! Back to the dock, measure the boat, sure enough, that forestay had elongated so much that he was raked nearly 4"....uh oh, thats more than the 1.8" of stretch we calculated earlier.... must have been the splices. Ok, lets shorten the forestay by tying knots, re-calibrate, and get back on the water... they didn't want to waste time with this as we were getting coached by an olympian and world champion in the 470 class. So, solution implemented, they go back on the water....

Same thing happens. They end up doing this fire drill 3 or 4 times and totally waste their day on the water.

So what went wrong? If you go by the manufacturers rope selection guidelines, they did nothing wrong. What they missed however was the yield strength of their line choice. UHMWPE lines are notorious for their low yield strengths....its about the worse hi-tech line you can choose for standing rigging. You have to size it way too big if you want it to stay a consistent length throughout its life. Its great for things that are easily trimmed though which is why its so awesome as a sheet or for other running rigging

Sorry that story was so long, but it goes to show...terms like stretch, constructional stretch, creep (when used in the manor that sailors use it) are all bullshit and don't tell you a thing about the material.

If you are making a technical materials decision, you have got to suck it up and get technical yourself.

 
Sorry that story was so long, but it goes to show...terms like stretch, constructional stretch, creep (when used in the manor that sailors use it) are all bullshit and don't tell you a thing about the material.

If you are making a technical materials decision, you have got to suck it up and get technical yourself.
Sorry man but I have to disagree, I think that there is enough information available to make an educated decision about lines today. After reading what you wrote about your friend, the bottom line is that even given all of the information available today, your friend still didn't make an educated decision otherwise he wouldn't have picked a line for a headstay that experiences creep.

The 505 used what 1/8" 1x7 wire headstay? Well while 1/8" dyneema may have higher load ratings, etc... you have to go up a size when going from wire to rope in order to get the same working affect as the wire otherwise you will experience a LOT of movement.

Yacht Rigging has never been and never will be an exact science.

 

sloansailing

Anarchist
855
0
Anacortes
The 505 used what 1/8" 1x7 wire headstay? Well while 1/8" dyneema may have higher load ratings, etc... you have to go up a size when going from wire to rope in order to get the same working affect as the wire otherwise you will experience a LOT of movement.

Yacht Rigging has never been and never will be an exact science.
The question is what caused the movement? The topic of the thread was to identify and agree on defining terms. If it happened in only an hour of sailing then it is not "creep" as "creep" takes long periods of time at high loads to occur. Most likely it was "constructional stretch" as the braids of the line slowly compressed upon each other and thus the length of the line got longer. Presumably if this "constructional stretch" was eliminated by high enough loading for long enough time the line would not get any longer, but might start to "creep" if loaded enough for long enough, which is unlikely (IMO). Further, some of the "constructional stretch" might actually recur if the line is unloaded for long enough and the braid is allowed to loosen. This will happen with any 12 strand, regardless of fiber type.

Agree that rigging will never be an exact science and also that 12 strand rope (of any fiber) is NOT the best choice for standing rigging!

Where did the line fail in your tests of brummel splices?

 
Creep was not the mechanism. Constructional Stretch is a made up term. You size up from wire to rope because all synthetics have a much lower yield stress than wire. Yield stress is not a published number, if it were, it'd be a very obvious decision.

I know and understand that real world problems in any field are not merely solved by the science involved with them. It takes an artistic application of experience to truly find an elegant solution.

 




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