Really short dyneema with two eye splices

[sully75]

Yeah I don't think the issue with the bowline is that it will come loose but that you kill the strength of the line.

Btw regarding the short length of these tethers, on a small boat a 24" tether will have me fully over the lifelines. A 12" tether would allow me to go forward crouched most of the way and then I would tie into fixed tethers at the bow and mast that would allow me to stand up. Estar style. I'd only be using the fore and aft tethers in nasty weather anyway. I may end up having a 24" on my harness full time and leaving a 12" permanently attached to each jack line.


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[sully75]

Other issue is I have a lot of dyneema and a lot of time but no money.


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[fjwiley1]

But Sully, look at all the Fun you are having......that is better than money......

Life is good if you Keepa Smilin.......




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[sully75]

No complaints!!


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[UNCIVILIZED]

Hey guys, not trying to sound overly negative on this, just thinking aloud. That & I've a small touch of hope that those newer to sailing will learn something about the amazing miracle of Spectra/Dyneema, & it's exotic cousins. Plus a few of it's limitations.

First off, I can surely get where you're coming from, wanting a SHORT tether. Ones in the 3' & under category definitely come in handy for things like being the right length to lean against to be able to work at the mast (base). Whether you're reefing, or just trying to sort out the snarls which can form there from the 2 dozen or so lines in that vicinity.

So... that said, I'm thinking that a Loup would work if you serve both of the long legs together. The bits where the shackles aren't. As then there won't be any line hanging loose to snag on anything.
Or, in lieu of serving it like this, just take a spare piece of (outer) line cover, or tubular webbing, & slip the long "legs" of the Loup through it. Tossing a bit of stitching into things, to keep the cover in place.
- If I were to use this option, it'd be tempting to just purchase a Loup of the length & diameter of choice, pre-made (and with a built in cover, plus a built in load/wear marker, if I could find such).

And a short, say 2' tether, would work in theory (meaning likely give you sufficient length for bury) if you go with a sufficiently thin piece of Ultra High Modulus Dyneema. Like SK-90, New England Ropes - Heat Set Rope, Dynex Dux, or one of the other brands with a similar strength to diameter ratio.

The catch being, that to get a tether that short, spliced out of Spectra, & still get a decent amount of bury after you're done splicing, you're literally restricted to stuff not much thicker than dental floss. Like say 5mm (3/16") +/- .

And it'll be "fun" trying to lock stitch something that skinny & slippery on a sewing machine ;-) . Even the ones which some riggers possess, with the curved/tunneled out presser feet.

While I have ZERO hesitancies about using all/any of the ultra high modulus ropes for control lines, lashings, & hell, even rappelling (in an emergency on the tiny stuff). For me, 5mm +/- is just too skinny for me to have peace of mind in on a harness tether. Especially given how slippery the stuff is (both for me to grab onto, & ditto for the splices).

This coupled with the fact that the splices will only really be tested when things are in extremis, & encountering severe shock loads. Which isn't the splices' strongest suit. That, & for me at least, there's not a lot of "meat" in a 5mm or 6mm line to deal with abrasion. Okay, yeah, I'm officially a wuss... I'll give 6mm & up a try.

Also, anyone who's worked with the stuff, I'm sure, has seen how these lines fuzz up when put into service. And while this fuzzing doesn't do anything immediately catestrophic with regard to the strength of the line, how do you tell when it's time to retire a harness tether which is starting to do this?
Plus, I'd reckon that the fuzzing likely becomes more, & more significant, the smaller the line diameters to get.

I'm going off of swiss cheese memory here, but I think that in one of the more recent works, the Dashew's speak of using Spectra to make their own harness tethers. But obviously ones longer than 2'.

Aw shoot, enough of this thinking through a plan, & worrying about the strength etc., let's just use PBO. KIDDING !!!!!

[hugosalt]

[QUOTE=estarzinger;1661369]It would be reasonably slick if you bought one of the dyneema webbing climbing slings, and then ran a row of stitching down it, sewing the two sides/parts together but leaving the ends as loops. Not much extra to catch that way.

I make up various Dyneema tethers, storm mooring pennants(attach to
3 strand nylon pennant outboard of chock for less chafe issues)
as continuous loops (tethers) and eyes (mooring pennants) on each I
put tubular webbing. On the tethers makes nice loops on each end and
protects line inside webbing from wear/catching and with just a stitch or 2
to hold in place(sometimes no stitch) makes for easy inspection of
dyneema inside.
Put a lock and stitch tail of bury, not for strength but to help with slip
on bury.

[UNCIVILIZED]

If I at all gave the impression that stitching, or lock stitching a splice, or the buried tail of a splice was to be done to strengthen things, such wasn't my intent in the slightest.

I was always taught that in any type of braided rope which was spliced, the splice was lock stitched. And that it was even more important with the more exotic fibers, as when the load goes onto & off of a splice in something like Spectra, ironically it's under the lightest loads & when the load comes off of such a splice that it's more likely to come loose than when it's under any kind of real load, or an exceptionally strong one. It seems counter-intuitive, but I have no reason to make up such a thing...

So the stitching is there to hold things in place, in the structural framework of a splice in the cores of high modulus fibers, together, when they're lightly loaded..

This was taught to me personally, by Brion Toss. And he went so far as to show me, firsthand, with a non-lock stitched, quality splice in Spectra. Done not 2 minutes earlier in his shop, how a light cyclical loading could (and did) cause said splice to come apart AKA fail.
And when I say light, I mean quite literally, a few ounces to a few pounds (at least in that demonstration).

Also, the stitching isn't just to hold the splice together. Nor am I speaking only of High Modulus core splices here. You also do a bit of stitching as needed, by hand, & or machine (yes, at times both) to clean things up, and to have them remain that way. Particularly as, if you have a piece of cover or bit of core, hanging out of a splice, then right there is both the location, & opportunity for parts of the line to get snagged. And such is where the line/it's splice may begin to be taken apart by cyclical action. As well as friction (internal & external caused by said loadings/action. Regardless of rope type.

[hugosalt]

yes, yes very detailed civilized explanation coming from uncivilized.
I also just recently tested, to show my son, a no lock stitched splice on 1/2 dyneema to excess of 2,000 lbs. and then proceeded to take apart with 2 fingers. He gets it now.

[UNCIVILIZED]

One important thing came to mind about this topic recently. And it has to do with the care & stowage typical of/for harnesses & their tethers. Given that much of the time they're pulled out to be worn, it's usually pretty nasty on deck. Enough so that when you go below, if you have a foulie locker, especially a heated one, your harness is going into it right alongside your foulies.

The thing is, at temps above 160 degrees Farenheit, Spectra/Dyneema begins to permanently loose some of it's strength. And the higher the teemps, the worse this gets. So if your trick new Spectra tether goes into the drying locker with everything else, there's a risk. A small one, but one, none the less.

So if you've got custom Spectra/Dyneema tethers, please keep this in mind. And given that, why not make them out of Vectran (?).

[estarzinger]

I honestly doubt dyneema is going to see enough heat in a wet locker to lose any significant strength. 170F will not do it - see purple line on graph below (from Samson). And you are not likely to see more than that in the wet locker because the normal operating temp for the desiel engine is 180F.



However, if you prefer it, vectran would be fine, with a caution about UV - It is less slippery, so the bury splices are a bit more secure. It's only major knock is poor UV resistance - so if you were going to be wearing it A LOT outside in strong UV, dyneema might be preferred.

[UNCIVILIZED]

It's not something that I'd personally worry about. I just thought it prudent to put the information out there, as it's news to some folks is all.

The crazy thing about Spectra is that if you look at some manufacturers info, it starts to loose strength once it gets up to between 10 - 20 degrees C.

[estarzinger]

Originally Posted by UNCIVILIZED

The crazy thing about Spectra is that if you look at some manufacturers info, it starts to loose strength once it gets up to between 10 - 20 degrees C.

Source? Data?

Pretty much everything I have seen to-date (lie the graph I posted above from Samson) suggests you need 80C to have any significant impact on strength, but I am eager to learn if there is some real test data to support a lower 'caution temp'.

Paper with a bunch of test data here:http://www.bethandevans.com/pdf/dyneemaheat.pdf

[UNCIVILIZED]

First, to be clear, I'd be more concerned about throwing my Musto & Henri Lloyd gear into a drying locker than the other bits (including tethers). Smocks & Drysuits are Expensive... Spectra & Vectran etc., I can replace for a few $. That, & personally, I prefer a tether which I can get a grip on. So that when King Neptune's washed me to the end of mine, needs be, I can use it to haul myself back up to whatever I was working on at the time.

As to Spectra/Dyneema's heat sensitivity, the bottom line is that it's already lost some of it's strength by the time you & I have broken a sweat. Not permanently, or much, it needs to get a bit hotter for that. However, if you look at page 8 of the linked PDF which you site, http://www.bethandevans.com/pdf/dyneemaheat.pdf, one can see that the strength's' already beginning to drop off, really before they even begin to chart it, at 20 degrees C. And it goes down from there.
You can see a better picture of what happens to it strength wise here, on page 2 http://www.pelicanrope.com/pdfs/Dyne...Tech_Sheet.pdf in the graph over on the right hand side. And again, by the time it's warmed to 20 degrees C, it's physical properties are already headed downhill.
Here's another product spec sheet, from Honeywell, on Spectra & it's physical properties. http://www.honeywell-advancedfibersa...ide&download=1
At 60 degrees C, it's lost 20% of it's strength as compared to when it's 23 degrees C. And by 100 degrees C, it's lost about half.

I'm not up for the online, or phone call digging to find someone who both remembers this, & is also willing to admit it. However, not too long after Warpspeed came out, there was a cry by owners (owners with big $) to change the color of the jacket away from white, as being inside of the carbon fiber masts was causing it to look dirty.
Sampson was at first reluctant to do this as they were worried about strength loss via elevated temperatures. However, in the grand scheme of things, a few percent, which was primarily temporary, didn't prove to be a big deal. Particularly as witnessed soon thereafter, by the whole rainbow of colors of Warpspeed, & Spectra/Spectra blended cores & ropes which came out.

Still, what I was taught with regard to it, is not to leave it anywhere you wouldn't want to be yourself. Like say, shut in a car on a hot, or a very, very cold day. As in such circumstances, temps can & do get to the point where permanent damage can be/is done to the material.

[estarzinger]

^^ it is a not exactly clear, but I think we are mixing up two properties.

The one I was talking about was permenant strength loss at "normal operating temp" after a high temperature exposure.

I believe what you are pointing at is strength loss while at the high temp.

Those are two quite different things. And I believe your wet locker example more closely fits the first - heated in the wet locker and then used at "normal" temps.

In any case . . . It's not something I personally consider significantly worrysome for a harness.

[seandepagnier]

bowline and other knots will slip out before the rope breaks with dyneema.

It is best to use a figure 8, but other knots work.

I use short pieces of dyneema with a eyesplice in one end and a knot in the other for sail hanks.