temporary fixing of dyneema

[markxengineerin]

Ignore the van- it was only used on the first attempt as a moveable anchor point. I'm using 2 trees with a 3 ton come-along and can adjust the load to +/- 10 pounds of a target very easily. I am making and pulling the shrouds the same way, to the extent of my ability, but only done 2 splices so far, and they are 6 inches different. I think I must have made a typo or math mistake, trying again tomorrow.

I bet the issue w/ the Dyneema is that it's not round, something I noticed when it was coiled, but possibly also true under load. If that's true, I might get better results if I always measure on the smallest diameter, and hopefully it's consistent. Otherwise, the way this gauge works, I'll have to calibrate it for different non-roundness or accept the error.

[Benz]

^^ Six inches is pretty huge; with material as stable as Dux you should be able to come within a half inch.
What sort of boat are you rigging?

[markxengineerin]

Pacific Seacraft 37. A single cable clamp holds 2000 pounds, when torqued down with a 3/8" ratchet and a vice grip to counterhold on the clamp. A lot more than I expected!


It's not the source of my huge error, which has to be a typo, but I think 3 of these cable clamps in a row is going to be a better solution than the finger trap style bury for a "temporary grab" as originally posted. The finger trap (aka whoopee sling) isn't as efficient because it messes up the set of the line, which matters unless you have 3-4 extra feet to waste on every line. The set is only restored by 2000+ pounds of force. I removed 0.5" of it at 650 pounds, then got another 1/8" at 2000 pounds, and called that the point of diminishing returns. The finger trap can be used, but then you have to pull on it again anyway w/ the cable clamps or other method to restore the set, so might as well just go right for the cable clamps and save a step. 3 cable clamps probably wastes 3-4 inches tops when the affected area is cut off, will find out soon.

[Breaking Waves]

Originally Posted by markxengineerin

A single cable clamp holds 2000 pounds,

Interesting - that is something I never tested.

But jfyi . . . . a waterbowline will hold ~45% of breaking strength, or almost 5000kg in your 11mm.

You would prefer to 'proof' pull these near their max working load, and I would guess 2000lbs is a bit light.

[markxengineerin]

I am going up to 4000 pounds each, and using 3 cable clamps per end for grabbing. Going from 2000 to 4000 stretched the line/splice combo out by another 3/8". I would like to go even higher, but have to draw the line somewhere, and my setup is limited to 6000 pounds anyway.

I ran into a problem today with not having enough line- need to get that worked out w/ Colligo before I can continue, but this stuff is still baffling me. It changes size slowly just by sitting there, very annoying when trying to get precise lengths. I'm sure it will be fine in the end, but there is a significant learning curve.

[Breaking Waves]

Originally Posted by markxengineerin

using 3 cable clamps per end for grabbing.

If you get a moment, I would be interested in a photo of how you have set up the 3 clamps in series. It is an interesting technique to have in the back pocket, and I should test it sometime.

You are using heat set dyneema I presume? I am surprised you seem to be having qa variation between sections off the same spool. A spool is usually pretty uniform.

New Dyneema under tension will grow and bleed off tension for several hours - if you really want to take the max pre-stretch out you need to leave it set up for like 12 hrs and pump the tension back to spec hourly. That is only worth doing if you really really need it nearest possible to the final length.

[markxengineerin]

Nothing fancy, just 3 in a row

A single one seems to take 1500-2000 pounds
A double slipped off once for me at 3300
I was going for 4000, so went up to 3, never had issues at 4000 pounds with 3 clamps.
A water bowline would do the job but I think waste more length. These fit in 3-4 inches.
Best part: the cable clamps are 70 cents each. I carry many of them in different sizes because they are so useful.

Yes, Heat Stretched Dyneema SK75 from Hampidjan, through Colligo.

"New Dyneema under tension will grow and bleed off tension for several hours - if you really want to take the max pre-stretch out you need to leave it set up for like 12 hrs and pump the tension back to spec hourly. That is only worth doing if you really really need it nearest possible to the final length."

I only want to be within +/- an inch, and don't hope to spend more than 10 minutes with tension on each one. Hopefully that's enough to produce a decent result. I saw the scale creeping down slowly with time (maybe 25 pounds every 5-10 seconds), but thought that could just as easily have been the chain digging into the trees. I did not spend long enough at 4000 pounds.

[Benz]

^^^If length is critical, I find it useful to leave the piece under tension as long as possible. Usually there will be one batch of loops or whatever under tension while I work on something else, and I give the tensioner another hit every so often. I'd think that it'd be worth it to ensure you don't bottom out your turnbuckles too soon.

[markxengineerin]

Ok. Coming back to the tension gauge issue- the dyneema is not round under load. Measuring .044" on the small axis and .053" on the large axis at 1800 pounds.
This varies the tension meter result by 0.009" translating to roughly 360 pounds.

Does anyone know if 11mm dyneema is expected to stay oval shaped or does it become more round with time? Anyway, the "error" looks easily correct-able by taking the average of 2 readings on long and small axis once they are identified.

[Breaking Waves]

Originally Posted by markxengineerin

Nothing fancy, just 3 in a row

Thanks. That did answer my curiosity - you are using the clamps basically as a stopper knot. Usually, with wire they clamp the tail to the standing part and make a loop. But the way you have used them is clever, it does minimize compromised rope length.

jfyi - to put in your tool kit in case you ever need, there is one actual stopper knot which will hold in bare dyneema - the "estar stopper" - would use less rope than the water bowline, probably around as much as your clamps perhaps a few cm more. It holds around 50% of line-breaking strength.

Originally Posted by markxengineerin

the dyneema is not round under load.

Does anyone know if 11mm dyneema is expected to stay oval shaped or does it become more round with time?

Interesting, if it is oval at 4000lbs, it sounds like it may be due to the braiding technique. If so, I would expect it to stay oval. I have not used Dux much, and the NER and Plasma heatset spools I have appear to be round.

[markxengineerin]

Good to know, I'll have to look that one up. Typos above, the diameter of the rope measures .440 to .530 not .044 and .053. It was about the same at 4000 pounds.

[Breaking Waves]

Originally Posted by markxengineerin

I'll have to look that one up. .

https://www.animatedknots.com/estar-stopper-knot

[markxengineerin]

i had not seen animated knots- really nice way of showing it.

I may have spoke too soon on the cable clamps: they started to break apart after the last disassembly today. They were holding 4K pounds, but crumbled when un-torqued. I'm not sure if it was a result of the tension or if I torqued too high. A better material is needed..



I finally figured out the cause of my inconsistency issues. This line absolutely must be pre-tensioned up to whatever max load is later going to be used (4k lbs in my case) before making any measurements. There's a 1% "permanent creep" after tensioning the new line, which means that if this isn't taken out, it totally messes up the initial understanding of how much a splice "uses up". This is a 6 inch error in 50' !!

A splice per Colligo's instructions in 11mm "uses up" a little over 41"


After pre-stretching to 4K pounds, and relaxing it, after 30 minutes, an undisturbed/untensioned line shrinks back down by 0.1%. 0.6" in 50 feet.

All of the above makes this a very time intensive process, lots of room for error, easily justifying the $45/splice fee Colligo charges. I don't think DIY is practical at all, if using turnbuckles and trying to hit perfect lengths, but I had no choice due to wanting to use my own terminators.

[Benz]

Originally Posted by markxengineerin

Ok. Coming back to the tension gauge issue- the dyneema is not round under load. Measuring .044" on the small axis and .053" on the large axis at 1800 pounds.
This varies the tension meter result by 0.009" translating to roughly 360 pounds.

Does anyone know if 11mm dyneema is expected to stay oval shaped or does it become more round with time? Anyway, the "error" looks easily correct-able by taking the average of 2 readings on long and small axis once they are identified.

The oval shape is an accident of the pre-stretching: the hot rollers they put it around tend to make it flatten as it's treated. I never bothered to look at a long-used piece to see whether it rounded up again.
The ones that stay round are passed though a final die to return them so after being pre-stretched, I suppose.

[Flagfish]

A floor jack did a bangup job for me.