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Brion Toss

Member Since 26 May 2007
Offline Last Active Jul 16 2014 04:34 AM
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Posts I've Made

In Topic: Rope/knot/splice load testing

05 June 2014 - 03:21 PM

The good news is that NER finally broke all the shackle and splice samples that I sent in. The bad news is that there was a serious mixup in the lab, and the results are essentially meaningless. Sigh. They'll be sending more rope, and I'll be assembling more samples.
Still awaiting results on some rope seizings tests, which apparently went better. Will keep in touch.

In Topic: Rope/knot/splice load testing

01 June 2014 - 05:21 PM

Anyone who's had to deal with a foul belay under extreme loads knows how important it is to belay correctly. The trouble is that there is such a plethora of opinions on what "correct" is. Fortunately, this can be quantified. I believe that a belay, by definition, can be applied to hold any magnitude of load, up to the break strength of the rope, can be left unattended, and can be eased and cast off , regardless of load magnitude. This can be done with a variety of belay tools, impromptu and otherwise, but cleats, belaying pins, bollards, etc. are highly-evolved items; it is just up to us to use them correctly. The initial turn, touching the far end of the belay first, is key. So is making a "C" turn first, instead of going straight to figure 8's (or making an "O" turn), in order to avoid binding. And I think that a finishing hitch is important, but only if there are enough figure 8's to generate enough friction that, regardless of the load, the hitch never gets loaded. Obviously this involves skill and judgement on the part of the operator, as different loads, rope consistency and belay point characteristics affect how much friction you need.
It seems likely that the reason there are so many demonstrably lousy belays out there is that sailors seldom encounter the kind of extreme circumstances where a lousy belay can kill you. But if you always take the trouble to belay well in normal circumstances, you will automatically belay well when it matters.
PS,
In case any of you were waiting to hear about the rope tests at New England, the samples have been there for a while, but have been bumped by paying clients. They assure me that they'll be breaking our stuff soon. Stand by.

In Topic: Rope/knot/splice load testing

19 May 2014 - 01:39 AM

Robc, on 12 May 2014 - 22:55, said:
With regards to dogbone loops,
You do gain strength as there is no knot to reduce strength, you end up with a much stronger set up, as long as the dogbone can take it.

Strength numbers for these aren't all that impressive, actually. For instance, a Harken Loupe, 10mm, has a working load of 5,645lbs. Much weaker than what we've seen in tests here, assuming a 2:1 safety factor. Granted, that 10mm includes the cover, but then you have to have the cover -- and the dogbone -- to make the thing work.

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Two other reasons to use them, apart from ease if use with cold hands;
They are much more slimline when you start using bigger diameter rope. A button knot can be a great thing to catch halyards on when prepping for a spin hoist for example.

We have differing experiences here. At least the self-closing shackles seem as easy as dogbones, cold hands or no. And it might be that oversize shackles will be more likely to snag things...

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Also when it has been heavily loaded, a big button knot hitting you in the head hurts just as much as a carbon dogbone in my experience

Actually, anything can have a damaging or fatal impact if it hits you at sufficient speed. Limbs and necks have been broken by flogging ropes, and we usually think of that as soft. The difference with a soft shackle is how unlikely it is to cause damage if it hits you at relatively low speeds (which are more typical, I think).

In Topic: Vang - preventing twisting on 8:1 purchase

04 May 2014 - 11:47 AM

One other factor is how the rope is coiled; "normal" coiling, evolved for 3-strand rope, will put twists into braided rope. Work any twists out of the whole run, then either coil over-and-under, or figure-8. Or don't coil at all.

In Topic: Rope/knot/splice load testing

04 May 2014 - 01:02 AM

[attachment=206241:Segmented Otto Shackle.JPG][attachment=206241:Segmented Otto Shackle.JPG]Attached see a segmented soft shackle/sling, courtesy of Matthew Otto, a rigger who is currently finishing a new gang for the whaling barque "Charles W. Morgan," at Mystic Seaport. Otto is also an all-around gifted rigger, and innovative as heck to boot. The shackle/sling addresses the frequent need to have an adjustable-length sling. Yippees and Whoopees also meet this need, but not nearly as handily. One downside to the Otto sling is that it will undoubtedly be much weaker than the competition, but this can be taken into account when choosing material size vs. load.
As you can see, it is a series of carefully-spaced locked Brummels; the lanyard knot can fit into any space. Note also that the lanyard knot has a long tail left on it, to make it easier to grab the knot and pull it through.
A related note: you can find descriptions and instructions for the knots and splices being discussed here, plus many more, at http://www.animatedk...matedknots.com. Recently, for instance, the host co-authored a paper on the use of a Constrictor knot for surgical ligatures (!).