Loopie sling break strength

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you guy are still getting to deep. go shallow. both create a " chocking effect on the load bearing surface. in one "choke" the woopie sling has a part of line going through the bight. in the loopie the "choke" has two parts going through the bight. the bight is the cause of the reduced efficiency in the line. the rope will fail were the greatest amount of rope efficiency is lost. being that a cut in the line, a knot in the rope, a snag, or bight. most knots in the line cause a 50% efficiency drop, most hitches cause a 20% reduction in efficiency. a "chocker" effect on the line causes a 40% reduction in efficiency.

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Hi,
Some truth to what you say, but I don't think it accounts for results taken in the absence of any "choke".
Fair leads,
Brion Toss
 
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Okay, sorry I asked. It seems I've opened a can of worms. I was simply questioning the comparitive strengths of the loopie and whoopie. Thanks for all the info. It does help me to understand it a little better. I still cannot understand how a line running over a block, with each leg supporting 100# does not have 200# effectively applied to it at the top, as this is the amount of force applied to the blocks anchor point.

However, I am satisfied that you got the math right. I have no way of proving one way or the other. I just wanted to make sure that I was staying within the proper working load limits of the loopie. As I said before, I perceive the loopie's eye and the whoopie's eye as being the weakest point, as that's where the block's sheave is going to impart all its force.

Thanks for all the input, and by all means, if anyone has anything to add, keep the discussion alive.

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Hi there,
Thank you for opening this particular can of worms; it has been most instructive for me as well. As for comprehension, keep chewing, you'll get it. It might be helpful to imagine that, as a line goes around a corner, it "deposits" energy, expressing it as compression. So in the case of that eye, the line doesn't take it, uninterrupted, all the way up to the top of the eye, and then suddenly collide with forces coming the other way, and decide to make a right angle turn. Instead, it starts "dropping off" energy as soon as it passes tangent with the bearing surface, much as the weight of flowing water is distributed throughout the arc of a curved pipe. You are correct in seeing that the load has to go somewhere, it's just going to unsuspected places.
Fair leads,
Brion Toss
 
First of all, I really appreciate that you are willing to take the time to engage in a lively and very technical discussion! I love this stuff, so I will probably drink you under the table.

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And neither the bight (by which I assume you mean a choked attachment) nor the tree keep the core from pulling out,per se. That is,it is easy to achieve maximum splice efficiency without the presence of either, though they can provide backup security.

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No, I did not mean a choked attachment, but I probably could have been clearer. I was trying to point out that the loopie is not intended to be used as an open loop. If I wanted to really put a loopie to the test (as I have done a number of times in one form or another), I would hook it up as an open loop and make sure that the spliced part was straight, not part of a bight, and finally I would make sure I installed pulleys at the two load points, not a shackle of some kind. This is the worst possible case, and the loopie will slip. Introduce some friction by using shackles (not girth hitched) at the load points instead of pulleys, and maybe the loopie will hold. Introduce more friction by putting a bight in the spliced section and applying the load there, and it will almost certainly hold. Add a mountain of friction by bending the whole works around a tree and further bend the shackle-holding bight through the spliced-section bight, and God can't pull it apart. The point is all those curves are doing something useful, and without some help the loopie can slip.


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Oy. First, the absence of the eye at "T" changes how the load is applied so much as to make "T" meaningless. In a conventional splice or a whoopie, half the load is applied by what is more or less an appendix in a loopie. But in all cases, the splice works because of friction generated along the entire length of the splice. Stitching in a conventional splice has no bearing on ultimate splice efficiency; it is there to make sure that the splice doesn't slip before enough load comes on to clamp the outer part around the inner. It serves no other purpose.

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Caramba. I agree that in a normal eye splice the stitching is just there to keep your dog from pulling the splice apart. But we are talking about an eye splice (loopie) where half the eye has been cut away, leaving just the appendix you mention. Now there can be no tension on the appendix, the missing leg of the eye, and we have a whole different animal on our hands. As I remarked in an earlier post, the loopie is like an eye splice with the entire load on the buried part. Here the stitching does do something.

I have done the following experiment several times with consistent results: Take two pieces of Tenex or Amsteel Blue and bury one in the other as if to make a splice. Now measure the force it takes to pull the core out, making sure the spliced area is not disturbed in any way. Let's say it takes 8 lbs to cause slippage. Repeat the exact same experiment, this time with 3 stitches of 2-lb. test sewing thread applied to the throat of the "splice." Now it takes 100 lbs. to pull the core out! Repeat again, this time with the 3 stitches near the end of the buried tail. Now it takes maybe 15 to 20 lbs. to pull the core out.

This experiment is precisely the worst-case loopie test--a straight pull to extract the core and no friction within a mile to help out. Anyone can repeat this experiment with a couple of pieces of rope and a bathroom scale.

So, back to the case at hand, if we apply this result to the question of where we should put a bight in the loopie sleave for the purpose of applying the load, it would seem it should be near the throat end, where I placed the arrow, not near the other end with the "T." The assumption is that this loaded bight is a bit like stitching--it creates friction that tends to lock the core and cover together. It should also have the big multiplier effect seen in my simple little experiment.

Hooray for the loopie. Not only is it a cool working tool, but a cool experimental one as well. The normal eye splice is such a well-behaved and predictable structure the inner physics is somewhat concealed. With the loopie it is all out there in the open, ready for someone with time on their hands to try to figure out the puzzle.
 
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this is a very boggling concept.

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i agree...i want some video of some testing pick some cars up with some loopie slings
 
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...I was trying to point out that the loopie is not intended to be used as an open loop.

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Oh, I don't know. It certainly needs serious attention to prevent slippage when used this way. I think of it as analogous to installing cable clamps to form an end-to-end splice, instead of an eyesplice. There, just as with a loopie, all of the load comes on one leg. This means you need to generate more friction for the clamps to hold, as some folks have discovered to their misfortune. With an eye -- in cable or rope, only half the load is going into pulling the end out,while the other half, at least in braided rope, is busy tightening the splice. But with an in-line configuration it is all trying to pull the end out. Since the splice can't resist this until there's a lot of tension on the line, you have to have some means of generating friction meanwhile. With a conventional splice you can use stitching, or a locked Brummel better still, but these options would disable the loopie's versatility. Thus getting the splice on a bearing, and massaging the slack out, and maybe taking an extra long tuck for good measure. You also might want to keep it away from your dog.


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...if we apply this result to the question of where we should put a bight in the loopie sleave for the purpose of applying the load, it would seem it should be near the throat end, where I placed the arrow, not near the other end with the "T." The assumption is that this loaded bight is a bit like stitching--it creates friction that tends to lock the core and cover together.

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I see what you are saying, and it might in fact make a difference. So far I've been more concerned with keeping any slack from reoccurring after I've massaged it out. If the "throat" is down and the standing part that exits the splice is up, and I put the bearing on the throat, then the weight of the standing part can easily cause slack in the splice. So I have been putting a Rolling Hitch around the throat leg with the appendix, to keep it in place, massaging the slack towards the running part, and then positioning the bearing just shy of the running part. The heaviest thing I've picked with this setup was probably the mainmast out of "Odyssey" -- less than two tons -- so field experience has not been on the extreme side. But I did send a couple of samples to New England Ropes for breaking, and as I recall they held, in the open, to something over half the ultimate load before slipping. I hope to repeat the tests, soon, this time playing with putting the splice on various bearing points, and also to set up a protocol for massaging slack pre-test, whether the splice is in the open or not. Other tests (by Yale and others) amply justify their double-what-a-Whoopie-can-do rating.
Fair leads,
Brion Toss
 
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