1/4" dyneema lifeline questions

[rdykiel]

Thanks - AmSteel and STS-12 have the same breaking strength (8.5k lbs in 1/4) so I was wondering the difference. So many things to learn, so little time :-)

[Brion Toss]

Hi again,
Actually, STS is much stronger than the Samson (12,000lbs vs 8,600), but the most significant difference for this application is constructional stretch, which isn't stretch at all, but rather the effect of strands settling into place under load. For the Samson, you can likely count on about a foot for every 50ft. of run; for the STS, a third or less of that.
Note also that your splices will cause the rope to shorten by an inch or more, again depending on the material, as well as the length and degree of taper in your splices. A little experimentation will reveal how much shrinkage you get from your splices.
Ain't learning grand?
Fair leads,
Brion Toss

[rxc]

I am doing the same project for my boat, and have a problem with one of my gates. It is only about 23 inches wide, so I cannot do the standard 72 diameter bury on both ends . I am using 7mm dyneema.

Does anyone think that it would be OK to do a 36 diameter bury on each end and then stitch the tails and sieze the throats of the eye splices? This gate is across the stern of the boat - not the sides.

Edit: I just realized that I could also do a Brummel splice with a short tail, which could even be stitched, as well. Any thoughts?

Edit 2: Upon more thought, it has finally occurred to me that I could use a long bury eye splice to insert a thimble around the bails on my bow pulpit, where the original lifelines were attached. I have found a source for 316SS thimbles that are not closed, so it appears that I could make the eyesplice around the thimble and thru the bail, thus eliminating the need for lashing. I could even stich this splice for extra safety. Does this sound like it would work? I have an eye-stud at the other end to do adjustments on the lifeling tension.

[benz]

For something like lifelines, especially with such thick line, you need not take the bury to 72 diameters. A neat trick is to taper shorter than the 72 diameter splice allows, then have the tapers overlap one another a little in the middle of the standing leg. I have tried making this sort of thing with no taper at all so that the line ends butt against each other inside the piece, but unless you can put a serious load on before you trim the ends of the buried lines, it's very hard to get just right.
However,for your purposes, a brummel and short bury should be just fine. I always like to put a whipping on even a brummelled splice.
Ben

[Brion Toss]

Hello,
This is a now-classic problem for Spectra lifelines, and we have tried a variety of methods to address it. One is the short bury option, and it makes some sense, given the relative loads. But it is, I think, a slippery slope; you can get away with it here, and then you see reports of tests showing even shorter splices holding to high efficiencies, and then splices get shorter and shorter until one fails, reminding us too late of the value of deep redundancy. I know, I know, it's just a gate, but my other objection is that cramming those two splices together is just ... inelegant. My usual practice is to make the upper and lower gates from a single piece, with the end passed through the standing part where it turns corners. But I also like the idea of a multiple Brummel, with a short bit of end buried for neatness.
No matter which option you choose, the really challenging bit is to have the gate come out the right length. Not much takeup available in those hooks.
Fair leads,
Brion Toss