Unveiling Bullseye Strops for low friction rings

[Seaworthy Lass]

I have changed the thread title. "Bullseye Strops" is what I would like to name these.
The term has a nautical connotation and as well it has the general current meaning of "hitting the sweet spot".

Thanks Dockhead and Stu .

SWL

[Dockhead]

Originally Posted by Seaworthy Lass

How about plain "Bullseye Strops"?
That is nice and simple and has a good ring to it. I like it very much .

They could be in the form of soft shackles or loops, retaining one or two objects or maybe more, I have not explored all the possibilities yet.

SWL

Distinct, yet nautically correct and with a very hold historical reference. Perfect.

[StuM]

Originally Posted by Seaworthy Lass

How about plain "Bullseye Strops"?
That is nice and simple and has a good ring to it. I like it very much .

They could be in the form of soft shackles or loops, retaining one or two objects or maybe more, I have not explored all the possibilities yet.

SWL

I think yo uneed to get the "diamond", weave" or "crossover" concept in there.
So how about "Bullseye Cross Strop"

[Alan Mighty]

Originally Posted by Dockhead

Concerning "vajra" -- an amusing and erudite word for this, but to my mind such fanciful appellations, referring to magical or religious concepts, do not add to clarity or understanding.

My arguments for vajra were sans magic and religion:

* it has a similar meaning to 'diamond',

* it has connotations about cleaving, defeating every other material, and

* the physical shape of a vajra: a diamond knob knot at one end and a diamond cage capturing the low friction ring at the other. A ready made icon for the brand and packaging.

[Alan Mighty]

Originally Posted by StuM

1540s, "to raise, lift, elevate," especially with a rope or tackle, earlier hoise (c. 1500), from Middle English hysse (late 15c.), which probably is from Middle Dutch hyssen (Dutch hijsen) "to hoist," related to Low German hissen and Old Norse hissa upp "raise," Danish heise, Swedish hissa. A nautical word found in most European languages (French hisser, Italian issare, Spanish izar), but it is uncertain which coined it.

Yes, that's the 'textbook' etymology. Sort of outdated thing you find in the OED or NED. Etymology has made progress since.

The story behind that, which explains why 'hoist' has no original language source, is what I wrote earlier - it is merely an exhalation sound used to coordinate effort among seamen who worked the North Sea together and came from different societies (and took the practice back to their own terrestrial communities - that's why versions of it show up in those languages).

[Seaworthy Lass]

Originally Posted by StuM

I think yo uneed to get the "diamond", weave" or "crossover" concept in there.
So how about "Bullseye Cross Strop"

I agree a good description would include "a cross over weave with a central diamond pattern to capture a bullseye", but the actual name need not be fully descriptive. I think most people will associate "bullseye" with "hitting the sweet spot". I had no idea that "bullseye" was a nautical term and I bet many other people don't either.

The name has lots of personal links for me as well, including shooting full bore on an intervarsity team many years ago. I think it is perfect.

I don't generally procrastinate . Rightly or wrongly, snap decisions are usually made when something appeals strongly or feels right. So "Bullseye Strops" are it .

SWL

[Seaworthy Lass]

Evans, you have missed out on the fun with naming.
Your input and load testing data has been invaluable, so thank you for all the hundreds of hours of work and for publishing the results online. Without the data (and the time you spend with your explanations), things like this cannot be easily designed, as it enables us to know what characteristics are necessary to maximise strength.

The usefulness of this Bullseye weave of course diminishes greatly without the previous extensive work put into making loops and soft shackles in dyneema, and by sailors like Dockhead making up these new systems and putting them through their paces and most importantly giving the rest of us feedback on the whole experience and ideas on how to improve things.

The constructive criticism offered by members here is also very useful. Comments by CruisingScotts when I was on the path of exploring lashings are what turned my thoughts right away from the whole idea of lashing a low friction ring to secure it in a strop, so I thank him for that. My darling husband just encouragingly repeated "there must be a solution, work on it, you can do it" and without that I would have given up. I am not known for my patience .

My weave pattern shown in post #1, which was developed based on all the above, is just one small step in advancing our knowledge of how best to work with dyneema.

Now we just need some load tests .

In meantime I will continue using a Bullseye soft shackle strop whenever we are sailing on our yankee sheet. Not a good spot for it, but the high loads mean it will get a good workout. It's only one test sample, but that is better than nothing.

SWL

[Cruisingscotts]

Great work SL!!!

Originally Posted by estarzinger

It seems a good solution. It just leaves the ring banging on the deck as an issue to be solved - I have seen racing boats with circular psa EVA pads under the rings to cushion them.

I've had good luck with a loose leather sleave over the ring and strop, it involves stitching... The sleave is slightly wider than the ring width and long enough to meet at the strop. you can stitch the courners tight in a way to make the inside of the sleave tight to the ring by coming in a little from the edge. This leaves the outer layer a little loose and makes a nice cushion. I'm sure the whole thing could be done with a synthetic material of choice on a sewing machine if leather and hand stiching was not your thing.

[Seaworthy Lass]

I have been looking more closely at predicting the strength of the Bullseye strops (all three).

Evans, your conservative prediction of 150% of line strength for the Bullseye soft shackle strop in post #1 seemed reasonable to me, given that the diamond stopper alone reduces the strength of soft shackles to about 175% of line strength in a 4 leg system (which all the common soft shackles seem to be, including that one).

Load testing will show exactly what this is, but I wanted to make sure I definitely had a good understanding of the effect of all the components in the system when it was actually in use, such as:

The attachment bend ratio
The bend going around the low friction ring
The throat angle
The diamond knot (the easy bit)
The Brummel lock
The noose
etc

I haven't got far .
No sooner than I think I am starting to get a grip on things, I find I am not .

Your two examples in post #90 were clear cut and what I had already come to understand , so I skimmed over example 3 in #91. I now went back to it and I am thrown:

Originally Posted by estarzinger

Let me add a third example . . . . A soft shackle, let's take a "not buried tails" design which put around two large bends will have a strength in the 150-170% (depending on construction quality) range of the tensile strength of the dyneema used.

If you put that around a small bend, it will reduce it by 50%, so 50% of original system tensile or 150% x 50% = 75% of line tensile.

So when we are referring to %, we need to be sure we are clear whether it is a % of original system strength or a % of line tensile.

Surely if the 4 leg system in a soft shackle (maximum potential strength of 400% of line tensile strength) is taken around a 1:1 bend, then the bend itself reduces the strength of the system by 50% to give 200% of line tensile strength not 50% of 150% to give 75% of line tensile strength, as you wrote above.

I think the strength of the soft shackle in your example should remain at 150% of line tensile strength going around a 1:1 bend, not halve.

Where am I going wrong?

A confused SWL

[estarzinger]

^^ take a look at post #100. I think I laid out the soft shackle case accurately there.

Yes, I agree that in the other post you cite I was wrong to take 50% of the knot strength rather than 50% of the main section strength (where the bend actually will be). . . . but see point just below - I do not know how far the knot and bend have to be to 'isolate' them from interaction. They need to be far enough that the load on the strands equalizes by the time it gets to the knot, and the outer strands of the bend are not still carrying disproportional load.

Unless the knot is very close to the bend - then there might well be an interaction between the bend and the knot. Then the outer fibers around the bend might then actually be breaking at the knot at 50% of the knot strength in that case. There have been some lab test results with lower than expected soft shackle strength, and I have suspected but not confirmed, that this might be the reason.

The question for your new design seems to me to be if the crossed strands effect the strength at all. Otherwise it is just a standard diamond soft shackle. I guess not and the knot is the weak point. But without testing I cannot say for sure, since I was surprised by other results.

[darylat8750]

Originally Posted by Seaworthy Lass

I agree a good description would include "a cross over weave with a central diamond pattern to capture a bullseye", but the actual name need not be fully descriptive. I think most people will associate "bullseye" with "hitting the sweet spot". I had no idea that "bullseye" was a nautical term and I bet many other people don't either.

The name has lots of personal links for me as well, including shooting full bore on an intervarsity team many years ago. I think it is perfect.

I don't generally procrastinate . Rightly or wrongly, snap decisions are usually made when something appeals strongly or feels right. So "Bullseye Strops" are it .

SWL

[Seaworthy Lass]

Originally Posted by estarzinger

^^ take a look at post #100. I think I laid out the soft shackle case accurately there.

Yes, I agree that in the other post you cite I was wrong to take 50% of the knot strength rather than 50% of the main section strength (where the bend actually will be). . . . but see point just below - I do not know how far the knot and bend have to be to 'isolate' them from interaction. They need to be far enough that the load on the strands equalizes by the time it gets to the knot, and the outer strands of the bend are not still carrying disproportional load.

Unless the knot is very close to the bend - then there might well be an interaction between the bend and the knot. Then the outer fibers around the bend might then actually be breaking at the knot at 50% of the knot strength in that case. There have been some lab test results with lower than expected soft shackle strength, and I have suspected but not confirmed, that this might be the reason.

Thanks. It was just post #91 that threw me. Post #100 was fine.

The above all makes sense, except for fibres breaking at 50% of stopper strength if it is very near the bend. That doesn't sound right as the stopper does not go all the way around the bend and therefore does not affect the entire bend, but I accept weird things may happen.

All this is very relevant to us, as for over two years we have been using a soft shackle as an attachment between our snubber and chain. Since starting to use a BB for this (30x line diam tail bury this year), out of curiosity every single day when diving I check it out underwater to see how it is behaving. It is always jammed right up the top against the bend.

If the stopper is in fact causing a 50% loss of system strength because it wants to settle near the bend (well, 40% loss in our case as we have a bend ratio of a bit better than 1:1 here), it is a considerable loss and needs to be taken into account.

Out of interest, I can report no soft shackles have ever broken, even with wintering at anchor in the Med the winter before last when we were still using an old style soft shackle with diamond stopper. 6mm dyneema have always been used, no thicker as it would not pass between the links.

SWL

[estarzinger]

Originally Posted by Seaworthy Lass

The above all makes sense, except for fibres breaking at 50% of stopper strength if it is very near the bend. That doesn't sound right as the stopper does not go all the way around the bend and therefore does not affect the entire bend, but I accept weird things may happen.

The cascade I am postulating is this:

(1)The "normal" stopper breaking strength (150-170%) assumes all the fibers going into the knot are roughly evenly loaded.
(2) The reason a tight bend reduces breaking strength is that the outside fibers are stretched and loaded (because they have a longer distance to go than the inside fibers) while the inside fibers are not loaded.
(3) So, if the knot is right up next to the bend, you might well have only half (the outside half) the fibers loaded going into the knot and the knot will then break at a lower load than if all the fibers were evenly loaded. The "outside" loaded fibers will break first and then the "inside" fibers get loaded and break. At extreme it would be as if one whole leg did not actually go into the knot - but I don't believe it gets to the half effect in actual practice.

I am pretty sure this effect is "real" to some degree, but I do not know its parameters - how much strength is reduced at what distances. And I don't have my test bench set up to examine it in further detail. But I am going to suggest from various tests that the effect could be up to 20% (of line tensile) - eg reducing a well build 170% down to 150, or a 150 down to 130. That is my best guess.

[Seaworthy Lass]

Originally Posted by estarzinger

The cascade I am postulating is this:

(1)The "normal" stopper breaking strength (150-170%) assumes all the fibers going into the knot are roughly evenly loaded.
(2) The reason a tight bend reduces breaking strength is that the outside fibers are stretched and loaded (because they have a longer distance to go than the inside fibers) while the inside fibers are not loaded.
(3) So, if the knot is right up next to the bend, you might well have only half (the outside half) the fibers loaded going into the knot and the knot will then break at a lower load than if all the fibers were evenly loaded. The "outside" loaded fibers will break first and then the "inside" fibers get loaded and break. At extreme it would be as if one whole leg did not actually go into the knot - but I don't believe it gets to the half effect in actual practice.

I am pretty sure this effect is "real" to some degree, but I do not know its parameters - how much strength is reduced at what distances. And I don't have my test bench set up to examine it in further detail. But I am going to suggest from various tests that the effect could be up to 20% (of line tensile) - eg reducing a well build 170% down to 150, or a 150 down to 130.

Oh, yes, I can see this scenario possibly happening if the stopper is right at the side of the bend. If it falls at the apex itself the problem disappears, as no fibres are actually going around the bend.

The stopper sits in the worst possible spot with our snubber. This may be recent. Looking at it, it is quite possible that the dreadful plastic thimble is making it worse, as it has squished together, not allowing the stopper to ride higher. Up until recently I had a largish SS thimble in there. I didn't have one on hand when I spliced the last eye on the snubber. I have kept meaning to fix this and have not got around to it .

The stopper very likely falls in that spot though as the person at the bow is leaning forward to attach it and secures the stopper closest to where he can reach. A high load is almost immediately applied when this is done, so it locks in the same position each time.

Anyway, for whatever reason the stopper is in the worst spot in an application where maximum strength is needed .

SWL

[Jim Cate]

SWL, if you don't want to use "diamond" in the name, you could substitute "rhomboid"...

Jim