Low Friction Ring strop methods survey

[Breaking Waves]

Better tapered whipping - eliminated the pin end weakness and improved resistance to whipping sliding.



Has a cross over bury, which is hidden around the ring.

Middle whipping of doubled 1mm Dyneema fixes the geometry from this whipping to the LFR, so the tapered whipping can be made to the exact geometry to hold ring while not squeezing the strop (if it squeezes the strop it will be under pressure and either slide or break when the system gets highly loaded.



The tapered whipping of 275 para cord - a little stretchy so it can adopt a little when things load up. Only thing I dont yet like is how I finished these ends - not very elegant yet.



And the pin end, is the two separate strands to improve D/d, over what it would be if one were buried inside the other.

[Breaking Waves]

In terms of strength per construction effort, this seems pretty hard to beat.



The webbing is a Dyneema climbing loop - pre-sewed. This is 8mm wide, you could use wider with bigger rings.

This 8mm climbing loop is rated at 22kN (4945lbs). This is a double loop, so let's say around 9000lbs.

To hold the ring in place I have just sewn Dyneema thread back and forth inside the ring edge.

[Breaking Waves]

Here is the plan for the follow-up test with improved strops:



Sample sets:

A1 - Tapered whipping - loop around pin
A2 - Tapered whipping - cow hitch to pin

B1 - Loose double splice - loop around pin
B2 - Loose double splice - cow hitch to pin

C1 - Tight double splice - loop around pin
D1 - Soft shackle - loop around pin
E1 - webbing - loop around pin

Sample sets A & B will give us information on cow hitch strength,
Sample C will give the worst case information on 'too tight' loops - these are designed to break at the splice neck.

All designs have double strands full around strop to try to eliminate the pin end breaking we found in the last test.
These designs (except the webbing which is dead easy) are a bit more complex to make & require a bit more skill, but they are not rocket science and pretty much anyone can do it.

Note: the ring in the bullseye in the photo is a placeholder. I will replace it when I get a couple more of the bigger tylaska ones.

[thinwater]

Originally Posted by Breaking Waves

In terms of strength per construction effort, this seems pretty hard to beat.

Attachment 193467

The webbing is a Dyneema climbing loop - pre-sewed. This is 8mm wide, you could use wider with bigger rings.

This 8mm climbing loop is rated at 22kN (4945lbs). This is a double loop, so let's say around 9000lbs.

To hold the ring in place I have just sewn Dyneema thread back and forth inside the ring edge.

Attachment 193468

In fact, I've done that and variations for many years.




For smaller sizes, take your ring with you to the climbing store, and often the ring will pop right into the sewn loop on the end of a quick draw, giving you a 30-second, $6 solution. I often seem to have extra draws, so this is free! (the cheapest way to buy carabiners is often in quick draw sets, and you don't need all of the slings).

[Breaking Waves]

Originally Posted by thinwater

In fact, I've done that and variations for many years..

Is there test data in the climbing community on how much strength loss in that cow hitch to a bail (and is it different to the loss in cow hitching two loops together)?

That throat - is it a whipping or sewing, or some of both?

I thought the “inside the rim” sewing I did was reasonably good - holds the ring well, not loaded so does not need to be anything special and not creating any (significant) stress riser in the webbing.

[Seaworthy Lass]

We have been busy the last few days antifouling so my mind has been free to wander (always dangerous ).

Breaking Waves, I keep going back to this post of Starzinger’s:

Originally Posted by estarzinger

This is a bit more complicated that that - for instance if a loop is around a 1:1 padeye, the strength is 100% (or 95%). But if that loop is around a payeye in a cowhitch it would be 85%.

You say this comment was not based on load testing as I thought, but instead on Samson’s findings with a rope cow hitched on a rope, so I tried to find the source.

Given your recent load test results, my instant reaction a few days ago was that Starzinger must have been referring to system strength with the latter percentage, as the cow hitch on the LF ring (essentially a big bail) did not break even at 180% line strength, but reading Samson’s actual comments, this seems not the case. It is line strength he was referring to.

I have reproduced Samson’s remarks about cow hitches below.
Both the diagram and photo to the right of it do not show a “proper” cow hitch at all, it is in fact what I have recently found out is called a “strop bend”.

If seems that absolutely no load testing results have ever been reported on actual “dressed” cow hitches, whether they are rope to rope or rope to hard object. Are you aware of anything at all?

I am speculating that there is a small chance that a dressed cow hitch may be stronger on a rope than an undressed one ie a strop bend. The reason for this is that a dressed version creates an “eye” where the line is doubled up, reducing load. For me this would explain why your cow hitch on the LF ring did not break at 180% of line strength.

What do you think? My understanding of how ropes behave it still very weak despite a keen desire to better this, so my comment above may be another of my stupid ones made while struggling, but to me it seems not impossible.

I am raising this issue as apart from the fact that cow hitches are used so widely by cruisers when attaching soft loops to objects or other ropes, it is very relevant for series drogue construction. I would very much like to make the correct choice there regarding knot construction so this issue is bothering me.

SWL

[Breaking Waves]

Originally Posted by Seaworthy Lass

antifouling

You are probably better at that than I was. I always got just about as much on me as on the boat. What is the latest best stuff to use on an aluminum hull?

Cow Hitch . . . .

On the recent LFR result . . . be aware of two things:

#1 these samples were gaskets and had bury around the ring, unlike in a normal spliced loop - so it is 4 strand strength as the baseline rather than the two strand strength base in a spliced loop.

You could try to extrapolate the samson 85% to this 4 strand case - 85%/200% = .425, and 400% x .425 = 170% strength in the 4 strand case, and 170% of 5400lbs (5mm strand strength) = 9000lbs. Which is higher than it actually broke at, probably because of this . . .

#2 The Huston guys reported it did not break at the cow hitch but rather at a metal crimp/kink formed when the LFRs distorted - it would have been stronger on a solid pin. I did not personally see this happening, so is harder for me to assess. The bury's were also perhaps not exactly equalized in length to the covers - I did not do any sort of special pre-tensioning on them, but that would be a secondary effect.

Both of those things make this result difficult to interpret as a test of cow hitch strength.

I am including cow hitched samples in the next test, but one of them include tapered overlaping bury's which are perhaps even a bit more difficult to interpret for pure cow hitch strength than the pure bury's in the prior sample. The other includes 4 pure naked strands - and might be a bit better but we are going to have a question about how well/perfectly the strand lengths were equalized. The cow hitches will all be on a solid pin, so we will at least not have any crimped rings at the cow hitched end this time.

Bottom line is these will not give a pure and clean insight into cow hitch strength. We need a test with simple loops without burys on solid pins to do that.

As to other tests - It seems clear that Samson has conducted several rope on rope tests - but I am not sure using what fibers (and it would make a significant difference) nor what combination of strop vs cow form. I don't see any sign they have conducted rope on pin cow tests. It also seems the climbing world has conducted rope on rope tests but not (that I have seen) rope on pin (or carabiner). Starzinger did do some cow hitch testing, pulling on one strand, to see when/if it slipped, as in use to connect a continuous jib sheet to jib clew - my memory is the cow hitch did slip but some other hitch (prussik) did not - but that is a quite different use case.

Bottom line cow hitching to a pin is not used much in high strength applications so (seemingly) has not been tested much (there must be some testing somewhere sitting on some shelf but I am not aware of where), and I don't know what the strength should be.

breaking wave

[StuM]

Originally Posted by Seaworthy Lass

I have reproduced Samson’s remarks about cow hitches below.
Both the diagram and photo to the right of it do not show a “proper” cow hitch at all, it is in fact what I have recently found out is called a “strop bend”.

I am speculating that there is a small chance that a dressed cow hitch may be stronger on a rope than an undressed one ie a strop bend. The reason for this is that a dressed version creates an “eye” where the line is doubled up, reducing load. For me this would explain why your cow hitch on the LF ring did not break at 180% of line strength.

SWL

Grog's comment (under Girth Hitch) is relevant:


https://www.animatedknots.com/girth-hitch-knot



The Girth Hitch should seem familiar because tying it employs the procedure we use to link two elastic bands. This familiarity provides a useful lesson. The two bands can be dressed to resemble either a Square (Reef) Knot or to take the form shown in the animation. To preserve strength when linking two slings, the knot must be arranged to resemble a Square Knot when it is then known as a “Strop Knot“.

Note, we all use the term "cow hitch" very loosely if you go by Ashley:


#1802 The COW HITCH differs from the STRAP or BALE SLING HITCH in that the pull is on one part only and the knot is tied in the end instead of in the bight.


(The strap hitch that we commonly call a "cow hitch" is ABOK #1694)



Here's some data using webbing:


QC Lab: Connecting Two Slings Together


It agrees with Grog's comment that the square dressed strop knot is significantly stronger than the undressed girth hitch.

[Breaking Waves]

^^

I just sent grog a note asking if he had a source or reference for his girth strength comments. I know he is busy redoing large chunks of his site but he usually responds pretty quickly.

I also talked with an engineer at Samson. And he said that the "85%" number had been around a long time and comes from tests well before Dyneema (and other high modulus ropes) were in widespread common usage. We do not know for sure but he speculated that the worst case dressing in Dyneema would be worse than this, which would be further explanation why the cow hitch in the recent LFR test failed before 170%.

We had just been looking at that climbing test in another discussion here (on scaling). Webbing does have meaningful different geometry and characteristics than rope. I'm not sure how applicable these results are to rope - they may be or they might not be. If I had to guess I would think they would be directionally/qualitatively the same but the numbers would be different - but that is just a guess.

The closest set of samples in this test would seem to be the 8mm dynex to 8mm dynex - it is still webbing to webbing but smallest width and both sides dyneema. It has (% of loop strength, NOT percent of webbing strength) Girth = 57%, Strop = 53% and climbers = 56%. I would honestly consider those statistically identical. Lets say 55% of loop strength, which equals 110% of single strand webbing strength - compared to samson's 85% (with we guess medium modulus rope). Honestly that is probably not then extendable to rope, and goes to show that webbing is better at small bends than rope.

It is interesting . . . . if yachting actually has a 'bend radius problem' . . . high strength webbing should probably be used more frequently. The drawback with webbing is it needs sewing rather than splicing, which (I think) takes more skill and care to get full strength.

[Seaworthy Lass]

Breaking Waves, many thanks for the explanation.
I know it takes time and patience to respond to basic questions.

Originally Posted by Breaking Waves

You are probably better at that than I was. I always got just about as much on me as on the boat. What is the latest best stuff to use on an aluminum hull?

“Smurf” has been my middle name the last few days .
The wet sanding actually had me looking the bluest (and it was the bit that was most exhausting), although that did at least scrub off skin a little more easily.

We used the old tried and “moderately true” Trilux 33 again (we have applied that ourselves each time over the last dozen years, except when this last boat was first built), but one of the alu boats that will cross the Atlantic this year has just had Sea-Speed V 10 X applied. It is two pack silane-siloxane compound that needs just one coat sprayed directly on freshly ground bare alu. It gives a glassy smooth coating that is clear. It will be interesting to hear how effective it is.

The only problem is that if it is less good for cruising yacht type usage, it would need to be ground back to bare aluminium fairly aggressively to get every spec off before anything else could be applied.

SWL

[Seaworthy Lass]

Originally Posted by StuM

Grog's comment (under Girth Hitch) is relevant:


https://www.animatedknots.com/girth-hitch-knot



The Girth Hitch should seem familiar because tying it employs the procedure we use to link two elastic bands. This familiarity provides a useful lesson. The two bands can be dressed to resemble either a Square (Reef) Knot or to take the form shown in the animation. To preserve strength when linking two slings, the knot must be arranged to resemble a Square Knot when it is then known as a “Strop Knot“.

Note, we all use the term "cow hitch" very loosely if you go by Ashley:


#1802 The COW HITCH differs from the STRAP or BALE SLING HITCH in that the pull is on one part only and the knot is tied in the end instead of in the bight.


(The strap hitch that we commonly call a "cow hitch" is ABOK #1694)



Here's some data using webbing:


QC Lab: Connecting Two Slings Together


It agrees with Grog's comment that the square dressed strop knot is significantly stronger than the undressed girth hitch.

Hi Stu
Thanks for all the info.

Looking at the strop knot’s far less “stressed” looking structure compared to the tight bends and highly compressed cow hitch, I had assumed this to be the case and so a variation of strop knot was I had decided to use at the Y junction of our series drogue bridle instead of the usual cow hitches used by the drogue manufacturers and DIY cruisers.

However, I know what the term “assume” breaks down to , so the results of the load testing on LF rings brought on doubts regarding my decision.

SWL

[thinwater]

Originally Posted by Breaking Waves

Is there test data in the climbing community on how much strength loss in that cow hitch to a bail (and is it different to the loss in cow hitching two loops together)?

That throat - is it a whipping or sewing, or some of both?

I thought the “inside the rim” sewing I did was reasonably good - holds the ring well, not loaded so does not need to be anything special and not creating any (significant) stress riser in the webbing.

I've seen numerous test. I think the average is about 75% strength. The more serious problem for climbers is that it changes the leverage on a carabiner. Not relevant on a u-bolt.


Just a whipping for retention. The WL on this eye is about 750 pounds, so not very high. In other applications (no photo) I've just pressed the LFR into the quickdraw eye.


The key is not using the strongest method, but knowing the load and knowing the strength of the methods you use.

[Breaking Waves]

swl,

I was just looking at that climbing webbing test a bit more closely, and there is a bit of odd procedure in a critical important footnote to the numbers:

"Note: For ease of comparison, strength values and reductions are compared to 22 kN—which is the CE minimum requirement for a NEW sling—so these numbers aren't actual reduction in strength of the slings, because it's possible that they are stronger than 22 kN when new—follow?"

This means these numbers are NOT compared to strand strength, but rather to a fixed standards number. This number is rather different than the actual strand strengths, for instance, 10mm dynex runner has an actual 27.4 kN strength - rather than this 22 they use in these calculations.

So, you need to be super careful when interpreting these numbers. For instance, this would probably totally screw up the size/scale comparison you were trying to do.

from an educational perspective - this observation was quite useful "It's interesting to note that when webbing sizes are mixed and tested in slow static pulls, the nylon failed, however under drop tower dynamic situations, the thin webbing failed. That just verifies that the rate at which loads are imposed on a system can make a difference in ultimate failure load and mode."

the climbers are much much better at considering and testing dynamic loading effects than anyone in sailing.

[Seaworthy Lass]

Originally Posted by Breaking Waves

swl,

I was just looking at that climbing webbing test a bit more closely, and there is a bit of odd procedure in a critical important footnote to the numbers:

"Note: For ease of comparison, strength values and reductions are compared to 22 kN—which is the CE minimum requirement for a NEW sling—so these numbers aren't actual reduction in strength of the slings, because it's possible that they are stronger than 22 kN when new—follow?"

This means these numbers are NOT compared to strand strength, but rather to a fixed standards number. This number is rather different than the actual strand strengths, for instance, 10mm dynex runner has an actual 27.4 kN strength - rather than this 22 they use in these calculations.

So, you need to be super careful when interpreting these numbers. For instance, this would probably totally screw up the size/scale comparison you were trying to do.

Oh, yes, I have now found that note. What a bizarre way of presenting figures!
I just cherry picked what I read in that article and so I missed that note entirely.

When comparing percentages I am learning the super hard way that assumptions can’t be made regarding what the % refers to .

Originally Posted by Breaking Waves

from an educational perspective - this observation was quite useful "It's interesting to note that when webbing sizes are mixed and tested in slow static pulls, the nylon failed, however under drop tower dynamic situations, the thin webbing failed. That just verifies that the rate at which loads are imposed on a system can make a difference in ultimate failure load and mode."

the climbers are much much better at considering and testing dynamic loading effects than anyone in sailing.

Not when it comes to snubbers. I think most cruisers are pretty good at considering dynamic loading then .

[Seaworthy Lass]

By the way, interestingly they also looked at a girth hitch (what I have been calling a dressed cow hitch).

Statistical significance is not listed, but there appears to be no difference between the girth hitch and strop bend for 8 & 10 mm dynex webbing connections.
Weirdly also no strength difference between 8 & 10 mm dynex as a % of 22 kN .