On my “Good Ideas To Do At Some Point In The Future Maybe When Things Quiet Down” (GITDASPITFMWTQ) list there has been an item that’s been hovering near the top of the list (above “Right grate American novel” but below “Close the door you’re letting all the heat out” ) has been a bench test to see how the different materials, treatments and brands of rope we use here at CYR perform in one of the most important metrics we have: stretch.
As cordage evolves, it almost always trends in 2 positive directions: lower stretch and higher strength. In the last couple years strength has become less relevant as the finished size of the rope becomes the limiting factor. If we really wanted to, we could have 4mm cores on 35′ racing boats and not be worried about it blowing up. Stretch has become more important. If you look at the “flavors” that Dyneema generations come in, the most recent iterations have become more and more stretch focused.
Dyneema SK60 (most similar to Spectra 750) was strong and light, but stretched, crept and wasn’t significantly stronger than the aramid fibers it was compared to. SK75 (Spectra 1000) was lower creep and much stronger. SK78 was lower creep, but not stronger (this is now the “standard” Dyneema from most marques). SK90 was stronger but no better on creep than 75, so has been supplanted by SK99 (better in creep and stronger). DM20 is… weird and I’ve never used it.
In the past year, I’ve made halyards with each of the ropes shown below. All of these are 3/16 or 5mm so comparable in size and would yield a ~5/16″ halyard. From the top:
MARLOW SK78 MAX The MAX line of Marlows Dyneema cores is their version of heat setting.
Defining characteristics: It’s black! The black comes off on your hands. Second stiffest rope in test. Looks cool. The braid angle is exactly average in this sample set.
Sizing: The 5mm core measured 4.4mm after being loaded. Round? Not really, unloaded it measures 5.3 one way and 3.69mm the other
Dumb observation: If this were a car, it would be an Audi A3.
ALPHA ROPES D CORE XTM 78
Defining characteristics: Silver. Not as stiff as HSR or Max, but stiffer than STS78. Longest braid angle. Smells nice.
Sizing: The 5mm measures 4.6mm loaded. Round? Meh. It measures 4.73mm one way and 4.2 the other.
Dumb observation: If this were a football player, it would be Odell Beckham Jr. Never heard of XTM either, but it’s good.
NEW ENGLAND STS78
Defining Characteristics It’s white (comes in 7 colors too) it’s floppy compared to the Vectran and the Heat Sets. Very shallow braid angle. Gets super stiff once loaded.
Sizing 4.9mm under load Round? Round!
Dumb Oberservation While typing this up, I dropped all the samples on the floor. I could tell the STS78 just by feel. I bet if I were to total up all the STS78 (aka STS75 aka Endura 12) I’ve spliced, it could go to Belmont harbor from the shop and back. Lets put that on the GITDASPITFMWTQ list!
Defining characteristics Gold! Much more abrasive than any of the Dyneemas.
Sizing 4.2 under load. Round? NO. 2.9mm one way, 4.6 the other.
Dumb Observation I totally forgot I had any Vectran in stock. It’s gone from about 40% of my high tech cordage to exactly .8% ( I have sold one Vectran rope all year) If this were a car it would be a Pontiac, because in a few years people will be all “Pon-Tee-Yak? What’s that?”
NEW ENGLAND HSR
Defining Characteristics It’s stiff! Really stiff. When you put a cover on it properly the crew all hates you for the first race because it only gets stiffer when covered.
Sizing: 5.1mm under load Round WOAH, they make round rope! 5.2mm one way, 5.3 the other. About as round as it gets.
Dumb Observation If this were a car it would be a WRX. Not exactly pretty, some people don’t like how they feel but does everything really well. And I sometimes cover it with orange cover, and WRX’s are often covered in tacky aftermarket gear as well.
So how did they do? Well, nothing broke and no one got hurt, which is good. Before I share any results though, lets talk methodology. Before we talk methodology, lets make a bunch of disclaimers for how rudimentary my testing methods are. Before we do that, have you listened to Astronautalis? He’s great, and I think it’s a damn shame that the yanswer to the previous question is always “who?”
METHODOLOGY I spliced all the samples into 10′ lengths. Then loaded everything to 1000lbs with a dwell of 30 seconds. The samples were length checked, and respliced to 10′. Why respliced? The construction stretch on new rope is huge. Even heat set ropes lose some of their “set” when coiled and handled. Splicing takes up a long length of rope, but then releases some of that once it’s under tension. Everything was loaded again and checked again.
To test stretch, I loaded all the samples to 200lbs, did the CYR Load Distribution Procedure (hit rope with mallet, kick hydraulic cylinder) then then loaded everything to 100lbs. A clamp was made off at the dogbone holding one end of the sample. Then the tension was added slowly until 1000lbs was reached and stable. The distance between the clamp and dogbone was then measured using a digital mic. The samples were then tested in reverse order after being left flat on the bench to minimize bending the rope. After that test, all the samples were taken to 2000lbs with a dwell of 1 minute, then retensioned to 1000lbs.
|ROPE||Stretch @1000lb||Stretch @ 1000lb 2||Stretch @ 1000lb after 2000lb load|
|Marlow MAX SK78||21.64||19.52||11.64|
|Alpha Ropes D Core XTM 78||24.32||17.53||9.78|
|New England STS78||29.9||22.93||14.33|
|New England HSR||20.35||14.42||8.84|
There is lots of interesting information here. All the ropes developed less stretch after being loaded, with the benefits increasing with the amount of load applied. This fits with what conventional but often ignored wisdom, as most riggers recommend preloading your halyards before use. For mains I like to load the main halyard around the boom at the mainsheet strop, then tension the mainsheet as hard as possible. For genoas, jibs and code sails I use the tack fitting, tension with a winch, then “banjo” the halyard from the foredeck by pulling aft on the line. For spinnakers I go get coffee and think about the weather.
The vectran stretched more, significantly more, than all the flavors of Dyneema. This is not a surprise, but keep in mind that Vectran should in theory have less creep than Dyneema SK75 and below over time, although SK78 and Vectran are supposed to be comparable. I will be modeling this, but since creep takes a long time to develop, I’ll be loaded the samples over a weekend and checking on Mondays.
The non heat set STS78 showed the next most stretch, but comes with a caveat. When setting the lengths to 10′ on the samples, I took nearly 100mm of initial set out of the STS78, whereas every other sample was more like 5-60mm after the splices were set. This means that if using regular Dyneema for length critical applications like strops or pennants, it needs to be set under tension. For best results I usually exceed the working load by 3x and have had good results with regular Dyneema after that.
The Heat Set Dyneemas all performed very well. The Alpha XTM stretch a lot initially but settled down after hitting our target load, and did particularly well after getting tensioned to 2x the test load. The Marlow MAX started better than the XTM but was overtaken after it was tensioned to 2000lbs. If you’ve got lots of experience with rope, this is very intuitive after handling the lines; the XTM starts out being much less stiff so it stands to reason that it would stretch more initially. The XTM braid angle however, is much more parallel to the rope, so once all the stretch is removed, it makes sense that it would show less load stretch.
The New England HSR did the best, especially once tensioned. This again fits with the “feel” one gets from the rope, as the HSR is the stiffest running rope I have ever used.
This was a fun test and will be updated as the creep results come in. The good news is that all the Dyneema lines performed really well compared to the state-of-the-art-circa-2005 Vectran. If we accept these numbers, and assume a boat like a T10 has these ropes on the main halyard. The T10 sailors, being good preppers and not tired from the party, preload their halyards before sailing. It’s windy out, but the ropes only stretch: Vectrus 130mm, MAX78 56mm, XTM78 47mm, STS78 69mm, and HSR 42mm.
As always, let me know if you have any rigging related bits for the GITDASPITFMWTQ list.
The overnight time on the bench has been surprisingly tied up, first with a steering cable and now with loops over the weekend, so I’ve decided to do some shorter term testing. Figuring that on a bad day, a windward leg of a race takes 30 minutes, I let each sample dwell on the bench for 45 minutes at 1000lbs after a 1500lb set. As it turns out, not much at all happens in 45 minutes.
|ROPE||LENGTH CHANGE IN MM||REMAINING LOAD @ 45 MINUTES|
|Marlow MAX SK78||0||982|
|Alpha Ropes D Core XTM 78||0||982|
|New England STS78||0||980|
|New England HSR||0||986|
The ropes didn’t move. Even a little. Testing was done with a metal square clamped to the bench even with the dogbone, and after the first sample I kind of knew the score, and that this test wouldn’t be very exciting. The most interesting thing is that the load numbers at 45minutes were down off of 1000lbs, but I’m willing to chalk this up to the bench itself, as there is always some movement and it’s not particularly exact as a dedicated testing rig would be. An interesting proof to this is that once the ropes were taken to 1500lbs, and then tension released to below 1000, then brought back up to 1000lbs, the numbers actually went UP before they went down. Could be the load cell itself, the loops, the winch, the tensioning rope (1/2″ vectran)
Here are some videos of the best and worst stretch from the test. This was done after the actual testing, so the clamp zero is a bit off, and the camera isn’t in line, but even so you can see the huge difference in stretch
With no change in dimension and negligible change in load, it seems like creep in the context of something like a windward/leeward race is not a significant factor. My understanding on creep is that it takes a combination of load/time and temperature to occur, and that it happens on the order of days and not minutes or hours. If I ever end up going upwind with the same tension on a halyard for days, please send help, as not only MIGHT creep be a factor but that sounds like an absolutely boring race and I don’t want to do it.
The interesting observation from the setup for this test was how much all the ropes initially moved when being spliced and set to 10′ lengths. So, for kicks, I also took a 6′ piece of STS78 and did the same test. This piece of rope only had a quick 1500 set, then was taken to 1000lbs. This one did grow, by about 28mm, and dropped tension to 658lbs. This fits my own experience in that prestretching any halyard on the bench makes it perform better once on the bench. Heat Set Dyneemas only really needs the ends stretched after splicing, and Vectran doesn’t seem to either (Dr. Bam Miller of Oyster Bay Boat shop thinks this is due to the higher coefficient of friction with vectran, but he’s not a real doctor and I don’t think Bam is even his real name.) Regular Dyneema does grow by quite a lot, the splices set as well as the rope itself elongating with load. The good news is that this settles down with a decent prestretch or lots of use.
My news for customers is this: get a Dyneema halyard. If you want more performance get a Heat Set Dyneema halyard. If you really want to come in and talk about creep for a boat that does buoy racing, please excuse me while I bang my head on the test bench.
Creep Update 1 HSR heat set Dyneema
The HSR sample was left on the bench at 1000lbs from Friday afternoon through Monday morning, the length was unchanged and the load was at 960lbs. Over 60hrs with no dimension change is pretty good! Assuming you were on a J105, and this was your main halyard, and the ENTIRE Mac race was upwind on the same tack in the same amount of breeze, you still don’t have to worry about creep in a halyard. So far this testing just reinforces my recommendation for heat set Dyneema halyards, aft standing rigging and critical control lines.
Creep Update 2 STS78 Dyneema
On Monday I loaded the STS78 sample to 1000lbs and planned to leave it there through Wednesday. As it turned out, it was left until this morning, so about 60 hours just like the HSR. In theory, this would be the most creep prone sample. Heat setting as a process removes the constructional stretch, but in theory also reduces creep since it accelerates it during production and aligns both the fibers and the molecuslar structure of the rope. Regular Dyneema should show considerably more constructional stretch, as well as more dynamic strech and definitely more creep. The constructional stretch on this sample should have been mitigated by all the cycling (multiple times to 1000, 1500lbs, once to 2000lbs) but I was still expecting to see some creep as compared to the Heat Set.
Instead, the sample is exactly where it was left on Monday, showing no dimension change. We’re at about 16% of break load. Although normal working loads for racing/cruising running rigging are about 20%, I feel that 1000lbs in this case is pretty indicative of a typical max-normal halyard load on a boat that would use 5mm Dyneema core.
UPDATE CREEP IN STS78 AT HIGHER % OF BREAK LOAD
Over the weekend (OH THE BEARS…) I decided to continue the creep testing by going with a higher-than-recommended working load on the STS78 sample. So far, the loads tested for creep have been loads you would likely see on the water with a 5mm piece of rope. No creep has been observed in any of the Dyneema lines, even in STS78 which is non heat set Dyneema and should in theory show creep. The fact that this piece has been prestretched by being cycled to 1000 (many times with long dwell), 1500 and 2000lbs has made stretch pretty minimal, but I was a bit surprised we couldn’t generate any creep (OR ANY PASS RUSH, BEARS).
To try and generate creep, I loaded the line to 40% of the breaking load (2440lbs). This is well above any SWL for running rigging, and would not likely be encountered on the water. After round 55 hrs the rope had elongated by just under 1mm (UNLIKE THE BEARS SECONDARY WHICH ELONGATED ENOUGH FOR 48 POINTS).
This is still really good! There was no prestretch beyond getting the rope to tension, so you’re likely seeing construction stretch as much as anything. Getting <1mm over 3048mm at this % of break load is incredible. You could debate whether we’re seeing construction stretch (probably) or creep (unlikely) but it’s nice to have this data (AND THE INEVITABLE TOP FIVE DRAFT PICK IN 2016).