Unveiling Bullseye Strops for low friction rings

[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.

[estarzinger]

And, if a long bury section is taken around a bend, I never tested to be sure, but am going to agree with SL's general assumption that it is the total diameter of the buried section that is relevant to the bend ratio - that at least is a conservative assumption. That is certainly the case of a Dacron double braid rope, and a burried section is similar to a double braid. But it might/may not be exactly correct - in a double braid the core and cover each take 50% of the load and that is probably often not exactly the case in a bury section.

In a rope construction with a high modulus core (like a dyneema core and Dacron covers) I presume it is the diameter of only the core that is relevant to the bend ratio, since the core takes all the load . . . But I have never tested that nor seen it discussed.

Interestingly in all the double braid ropes with dyneema core and dyneema cover I have seen - like NER wr2 - the core takes near all the load and the cover is there for chafe protection. So even in this case, it would be only the core diameter that determines bend ratio and not the total diameter of the rope.

[Dockhead]

Originally Posted by estarzinger

And, if a long bury section is taken around a bend, I never tested to be sure, but am going to agree with SL's General assumption that it is the total diameter of the buried section that is relevant to the bend ratio - that at least is a conservative assumption. That is certainly the case of a double braid rope, and a burried section is similar to a double braid. But it might/may not be exactly correct - in a double braid the core and cover each take 50% of the load and that is probably often not exactly the case in a bury section.

OK, so bottom line --

We need to avoid thin bails where possible. Maybe there is some kind of thimble we could use. Because most of the strops and shackles we are looking at achieve more than 50% of the theoretical strength (theoretical maximum strength is 2x the strength of the dyneema raw material), which means a thin bail can be a weak link.

AND

Make sure any tight bend is done with the thinnest part of the shackle or strop, not the part with a buried tail in it.


AND MAYBE

Be practical about all of this -- we might not care about the difference between 12 tonnes breaking strength and 15 tonnes of breaking strength if maximum possible load is 5 tonnes. Or if some other part of the system is weaker.


Is this all correct?

[Seaworthy Lass]

Originally Posted by estarzinger

^^ the confusion is based on what "100%" is . . . In some cases it refers to "100% of line strength - eg the rated tensile of the dyneema", and in other cases it refers to "100% of the system without any bends - eg a strop/ loop has twice the strength of the dyneema tensile, without any bends" so 100% in this second meaning is actually 200% in the first meaning - lol - is that at all clear?

Two examples . . . A line with loops on each end. With the loops around large bollards (big bends), that "system" will be as strong as the line tensile. The loops are double strength (eg 200% of line tensile) and the middle section between the loops is obviously line strength (eg 100%). Note- I am simplifying a bit here because the loop bury and taper does actually usually reduce the strength a little bit (5% or so) and this two loop large bend system almost always breaks at the end of the bury taper. . . . .now let's put small bollards with 1:1 bends on those loops, what happens to system strength . . . . The strength of the loop is reduced by 50%, but that loop was 200% (of line and of system strength), so those loops are now 100% (50% x 200%), and the whole system is still at 100% - note again it is actually all at about 95% because the 1:1 bend is actually just slightly worst than 50%).

Ok, second example - the entire system is a loop. Put around two large bollards, that loop is 200% of line tensile. Put around two small bollards with 1:1 bends that system is reduced by 50% and is now only 100% of line tensile (but you see it is still "100%" that is where the confusion is, but it is 100% of line tensile and not system tensile - now 50% of original system tensile).

Clear?

This is confusing - even colligo got this wrong.

I can see I will have to use my language more carefully.

Yes, that's clear. Thanks. That is basically what I wrote in my "Edited to add" above, after I figured it out.

That is what I meant in post #2 ie if the bend radius is 1:1, the strength of the diamond removable strop is reduced by 50% (I just confused everyone by writing "line strength"). The removable strop in this case has 4 legs, so potentially it could be 4x stronger than "line tensile strength". A 1:1 bend means it halves, so this reduces the removabke strop strength to 2x "line tensile strength".

I need to be more careful with my language too, as I confused you before you confused me .

Basically though, this means the removable Diamond Short Strop probably has a strength roughly twice that of the type of loop strop Dockhead is using if they are attached with a 1:1 bend. Is this correct? After your earlier comment that I misinterpreted, I assumed they would be similar if the same thickness of dyneema was used for both, as I interpreted incorrectly the 1:1 bend was not limiting the system.

SWL

[Seaworthy Lass]

Originally Posted by Dockhead

OK, so bottom line --

We need to avoid thin bails where possible. Maybe there is some kind of thimble we could use. Because most of the strops and shackles we are looking at achieve more than 50% of the theoretical strength (theoretical maximum strength is 2x the strength of the dyneema raw material), which means a thin bail can be a weak link.

From Evans's graph in his load testing doc:
Load testing
(graph attached below), a turning object (bail, thimble etc) with a diameter 3x line diameter would still only achieve roughly 70% of the strength of the dyneema loop you are using, that is 140% of "line tensile strength" if you could avoid the cow hitch. It would need about 6.3x line diameter to achieve 80% strop strength ie 160% of "line tensile strength". That is getting mighty big (a 50mm wide thimble for 8mm dyneema). Far too impractical.

I think you could stick to a 1:1 ratio and probably have around 170% of "line tensile strength" with the removable Diamond Short strop (trying hard here ).

[Tayana42]

SWL, Dockhead and Evans, I am so very impressed to watch you developing a new piece of sailing technology in public, right before our eyes. I've no doubt this will find its way onto many cruising boats in the near future.

Amazing...and it has no printed circuit boards😉.


S/V B'Shert

[Seaworthy Lass]

Originally Posted by Tayana42

SWL, Dockhead and Evans, I am so very impressed to watch you developing a new piece of sailing technology in public, right before our eyes. I've no doubt this will find its way onto many cruising boats in the near future.

Amazing...and it has no printed circuit boards��.


S/V B'Shert

Great guys to work with and very unstinting with sharing their time and knowledge.

I have had fun .

This Diamond Short strop needs load testing though. Any volunteers?
Given three things: the difficulty in restraining the low friction ring without a tight throat when a simple loop of dyneema is used, the losses in strength trying to connect this loop to the deck, and the fact that short not long connections are usually more necessary, I think the Diamond Short Strop potentially is very useful

A slightly longer version can be made that is a bit stronger if the tails are buried (use Evans's Overhand/Loop stopper or Brion Toss's Button stopper). Two Brummel locks would be needed for this though and I think a decent gap would need to be left in the locks to allow for load distribution if this is to work well. It would potentially be around 30% stronger I think.

SWL

Edited to add: is "strop" the right word for this system? I can't find a good definition of "strop". Relying on you here Dockhead .

[Dockhead]

Originally Posted by Seaworthy Lass

...

Edited to add: is "strop" the right word for this system? I can't find a good definition of "strop". Relying on you here Dockhead .

"Strop" is a proper nautical word for a short and strong piece of rope.

Here is a very old definition of "strop" which shows that it's an even far more proper word for this system than I imagined:


"nautical*A piece of*rope*spliced into a*circular*wreath, and put round a*block*for hanging it."

http://topmeaning.com/english/strop


How do you like that?


Sent from my SGP521 using Cruisers Sailing Forum mobile app

[Seaworthy Lass]

Originally Posted by Dockhead

"Strop" is a proper nautical word for a short and strong piece of rope.

Here is a very old definition of "strop" which shows that it's an even far more proper word for this system than I imagined:


"nautical*A piece of*rope*spliced into a*circular*wreath, and put round a*block*for hanging it."

strop meaning and definition


How do you like that?


Sent from my SGP521 using Cruisers Sailing Forum mobile app

I knew I could rely on you . All I came up with was references to razors.

Strop is not the right word then, this has not been sliced into a circular wreath, nor is it necessarily hung, although it could be. Nor is it a soft shackle. What would you call it?

[estarzinger]

Originally Posted by Seaworthy Lass

[B]Basically though, this means the removable Diamond Short Strop probably has a strength roughly twice that of the type of loop strop Dockhead is using if they are attached with a 1:1 bend. Is this correct?

OK, this is a useful example.

Dockhead's strop is relatively easy. The system with 'big' bends and excellent end to end splice should be 200% of line tensile. If it is spliced thru a 1:1 bail it will be reduced (by half) to 100% of line tensile. If it is cow hitched thru that same 1:1 bail it is reduced a bit further - Samson says to 85% (I never did a big enough sample to have a statistical result on that specific case).

The diamond strop (a 'conventional' soft shackle) around 'big bends' with excellent construction will be 170% of line tensile. The weakest point here is at the diamond knot. The noose is about 220% strength and the 'body' of the shackle is 400%. So if you put the body around a padeye with a 1:1 bend, that part of the shackle is now 200%, the noose is still 220% and the knot is still 170% - and the weak point is still the knot at 170% so that is where it will break. Edit: note this is a good reason to use soft shackle designs with 2 (separate) legs, at least where it goes a round the bend, rather than the designs that use one leg (with the other buried inside), which will have a worse bend ratio.

So, yes, the soft shackle will be stronger in that situation than the 'single' loop strop of the same size dyneema . . . . but you could make the loop strong stronger by simply using a 'double loop' - it would then end up at 200% and stronger than the soft shackle, and use about the same amount of dyneema (if they were the same length - which with a 'double loop' you could accomplish). I am a pretty big believer in using double loops when necessary, because beyond this point it also halves the load on the splice - and allows the use of thinner line which makes the bend ratio better.

And as Dock says - we may have 'enough' strength even in the weaker of all these options, and our anchor points may actually not be able to hold the strongest of these options - that was Allen's personal conclusion about the stronger shackle designs (eg that its extra strength was not necessary) but of course he does not have as powerful a boat with as high loads as either you or Dock.

[Alan Mighty]

Originally Posted by Seaworthy Lass

I knew I could rely on you . All I came up with was references to razors.

Strop is not the right word then, this has not been sliced into a circular wreath, nor is it necessarily hung, although it could be. Nor is it a soft shackle. What would you call it?

No, no, SWL. Dockhead is correct. Strop is a perfectly good term to use, especially for a spliced (not 'sliced') loop of cordage.


Let me take you through the history of the word.


First, I'll start by working backwards from the quote Dockhead gave you, about a circular wreath of cordage used to encircle a block. That's from Falconer's Dictionary of the Marine. As a citizen of what G W Bush in his inimical bumbling way called Austria, you SWL know that the National Library of Australia hosts the best digital version of Falconer's Dictionary, which Falconer first published in 1769. The NLA hosts a clean digital version of the 1780 corrected version. Of which every smart school kiddie in 21st century Aus is an expert user - an exciting time to be an Aus, eh? Check out the NLA's copy of Falconer's entry for strop at: William Falconer's Dictionary of the Marine, S, page 1309


Second, it's worth noting that in the 16th century or thereabouts, the majority of folk in southern England adopted a dialect mispronunciation of strop. Since those southern Englanders had more political and economic clout than the northerners, their mispronunciation became unfortunately the standard for what's jokingly called 'received pronunciation'. Hence the orthography and mispronunciation: 'strap'.


Third, note that the usage for a length of tanned animal skin against which a cutting edge could be rubbed to polish it, i.e. a 'razor strop', dates from the early 18th century (the first recorded instance is dated to 1702).


Fourth, in English strop started as a nautical word and has a thick history as a nautical word. The word was borrowed as a term for both generic and specialised pieces of harness gear for horses. But the rest is solidly nautical. It's a sailor's word, in other words.


The earliest recorded usage is in late Old English from about 1050 (the scribes did not always date their work). That first recorded use is in the form of a bilingual gloss between Latin and Ænglish and notes that the natives use the word 'strop' for a circle of cordage, a thong if you prefer, to attach an oar to the thole-pin of a boat. The Latin equivalent given by the scribe was, surprise, surprise, Struppus. I'll come back to that in #5.


From 1050 to Falconer in 1769, then to the 20th century and to now, the recorded use of strop as a nautical word is completely in agreement with use of 'strop' as an appropriate name for the piece of cordage holding a low friction ring. The explanation in Falconer's Dictionary is defining, but the term was also used for a wreath of cordage attaching a bobstay to a bowsprit for example.


Fifth, the etymological history leading to that earliest preserved written usage in about 1050 is not completely clear, but clear enough. Other economies that had sailors working the North Sea used versions of the word: Old French estrop, a loop; Old Low Germanic strop, stropf; and Portuguese estroppo, a rowlock strap (exactly the same use as recorded in Old English!). Latin struppus, stroppus, a strap, a band was likely the source of the Germanic and Romance words. And the Latin likely came from Greek strophos, laid cordage, laid rope, a twisted thing. An even older origin, around 3000 BCE, can be posited in proto-IndoEuropean streb, to twist, to spin or twist fibres (the key process in making cordage including the wonder of laid rope).

[Seaworthy Lass]

Originally Posted by Alan Mighty

No, no, SWL. Dockhead is correct. Strop is a perfectly good term to use, especially for a spliced (not 'sliced') loop of cordage.


Let me take you through the history of the word.


First, I'll start by working backwards from the quote Dockhead gave you, about a circular wreath of cordage used to encircle a block. That's from Falconer's Dictionary of the Marine. As a citizen of what G W Bush in his inimical bumbling way called Austria, you SWL know that the National Library of Australia hosts the best digital version of Falconer's Dictionary, which Falconer first published in 1769. The NLA hosts a clean digital version of the 1780 corrected version. Of which every smart school kiddie in 21st century Aus is an expert user - an exciting time to be an Aus, eh? Check out the NLA's copy of Falconer's entry for strop at: William Falconer's Dictionary of the Marine, S, page 1309

Hi Alan
Thanks for that excellent explanation and also for the link .
I was not aware of that online marine dictionary .

Dockhead called the simple loop system he was using, a "strop". This sounds perfectly correct to me.

Dockhead has not called my system a "strop", I did and I am still not sure this is correct, as it is not a continuous loop. It opens and closes.
Does the current usage of the word "strop" encompass systems that open and close? I need to get the terminology correct now, or I will never hear the end of it later .

SWL

[Seaworthy Lass]

Originally Posted by estarzinger

OK, this is a useful example.

Dockhead's strop is relatively easy. The system with 'big' bends and excellent end to end splice should be 200% of line tensile. If it is spliced thru a 1:1 bail it will be reduced (by half) to 100% of line tensile. If it is cow hitched thru that same 1:1 bail it is reduced a bit further - Samson says to 85% (I never did a big enough sample to have a statistical result on that specific case).

The diamond strop (a 'conventional' soft shackle) around 'big bends' with excellent construction will be 170% of line tensile. The weakest point here is at the diamond knot. The noose is about 220% strength and the 'body' of the shackle is 400%. So if you put the body around a padeye with a 1:1 bend, that part of the shackle is now 200%, the noose is still 220% and the knot is still 170% - and the weak point is still the knot at 170% so that is where it will break. Edit: note this is a good reason to use soft shackle designs with 2 (separate) legs, at least where it goes a round the bend, rather than the designs that use one leg (with the other buried inside), which will have a worse bend ratio.

Hi Evans
Thanks for all that.
That is the premise I used when I postulated that the removable Diamond Short Strop was twice as strong as a standard simple loop strop that was cow hitched on, such as Dockhead was using.

Originally Posted by estarzinger

So, yes, the soft shackle will be stronger in that situation than the 'single' loop strop of the same size dyneema . . . . but you could make the loop strong stronger by simply using a 'double loop' - it would then end up at 200% and stronger than the soft shackle, and use about the same amount of dyneema (if they were the same length - which with a 'double loop' you could accomplish). I am a pretty big believer in using double loops when necessary, because beyond this point it also halves the load on the splice - and allows the use of thinner line which makes the bend ratio better.

And as Dock says - we may have 'enough' strength even in the weaker of all these options, and our anchor points may actually not be able to hold the strongest of these options - that was Allen's personal conclusion about the stronger shackle designs (eg that its extra strength was not necessary) but of course he does not have as powerful a boat with as high loads as either you or Dock.

Yes, these systems using Dyneema are usually way stronger than needed for the application and yes, if in doubt, you could just use thicker dyneema or double over the loop, or alternatively lash on the ring somehow.

But I strongly disagree that doubling over a simple loop or using thicker dyneema is a better solution, regardless of boat size. It is worse in all regards, as far as I can see, apart from not needing to learn how to tie some kind of stopper knot and this is a super useful skill to have under your belt anyway when it comes to making soft shackles (although you could even skip this and make a longer variation using a toggle here instead of a stopper knot). I think any added complication with the Diamond Short strop is made up by the speed of making this compared to lock stitching buried splices for a loop.

This is the full picture:

Going with thicker dyneema in a simple loop strop to achieve the same strength as a removable Diamond Short Strop means:
• it is nearly 400% longer
• it is nearly 300% more expensive
• there is a significantly bulkier attachment at the base if it is cow hitched on
• there is the issue of retaining the ring well (this issue is what started my quest)
• it is significantly more time consuming if a long bury splice is used that needs lock stitching, rather than a weaker Grog sling
• it is not removable without reeving the line going through it

Doubling over a simple loop to achieve the same strength as a removable Diamond Short Strop means:
• it is nearly 50% longer (more when somehow attached)
• it is nearly 70% more expensive
• there is the problem of how to attach it at the base (a cow hitch can no longer generally be used, as the bulk would be horrific)
• there is the issue of retaining the ring well
• it is significantly more time consuming given lock stitching is needed
• it is not removable without reeving the line going through it.

The removable Diamond Short Strop can no doubt be improved, but even as it is, I see it as having huge, not minor advantages over loop strop systems for low friction rings.

SWL

[Seaworthy Lass]

Hmmm, after mulling over this, the Removable Diamond Short Strop is actually just a soft shackle in a new configuration and should be called this.

It needs a short easy name. The above is terribly unwieldly. Any suggestions anyone?

Also a name for the system of a long loop strop using the diamond weave pattern to retain the ring.

Also a name is needed for the connection between two rings using a loop and the same diamond weave pattern. StuM, you are an expert on knots - has anything like this been described in Ashley's?

SWL

This is a reminder of how the three look:

[Alan Mighty]

Originally Posted by Seaworthy Lass

Does the current usage of the word "strop" encompass systems that open and close? I need to get the terminology correct now, or I will never hear the end of it later .

SWL

I see your point: you see a distinction between:


(i) a spliced loop or circular wreath on the one hand; and


(ii) a lanyard that can be closed to form a loop by a knob knot and an eye splice (or, as in the case of the Antal Hook, an eye splice and a toggle).


That's the same distinction we have between (i) a block; and (ii) a snatch block.


I'll make a first diversion to point out that 'snatch block' arrived in nautical English about 1625. The qualifying adjective 'snatch' had been in nautical English earlier: around 1485 it shows up as a marker of things that could be quickly and easily attached to something else - and in almost all cases it involved use of a hinge. I have found it difficult to trace that word, 'snatch'; my best guesses involve a Middle English agricultural word from 1341 snasche, a hasp, a catch for fastening; and earlier Middle English snecchan, from 1225, referring to the jaws of a dog (which, like us, has a hinged lower jaw that can close on its fixed upper jaw; both jaws are not hinged, only the lower mandible).


And for a second diversion, I invite you to meditate on the word 'becket'. It's open to broad interpretation, verging on misuse. One word for that 'eye splice + knob knot' or 'eye splice + wooden toggle' fastening is, surprise, surprise 'becket'. The broad interpretation is that a becket can be almost anything that is involved in making an attachment or fastening. To cut the story of becket short, look at Billy Falconer's Dictionary of the Marine entry (from 1769): William Falconer's Dictionary of the Marine, B, page 131


I see no problem with calling your openable/closeable wreath of cordage a strop. Or even calling it a 'strop with a becket'.


Others will no doubt disagree.


The magic of English is that it is democratic (in contrast to a few other languages that have prescriptive overseers). The users rule. Sometimes distorting the meaning of words horribly. So we are stuck with words such as 'sanction' that can be used in two ways, one the polar opposite of the other! And words that have changed meaning over time, e.g. 'awful'.


As a guide to usage, I invite you to spend excess time (should you have any!) on two internet search tools:


1. A Google Image search of what 4x4 drivers call 'towing strops': https://www.google.com.au/search?q=t...i4DhYQ_AUIBigB


You'll see that not all strops are unbroken circular wreaths of cordage.


2. A Google Books ngram of how the word 'strop' has been used in the past 200 years (based on Google Books scans of printed works from 1800 to 2000): https://books.google.com/ngrams/grap...Cstrop%3B%2Cc0


Pick, say, the 25 years from 1975-2000 and click on that link. Then use the menu and choose 'Search Tools' and select 'Sorted by date' instead of 'Sorted by relevance'. Work through it quickly (ignore instances created because of an author surnamed Strop, and instances that are about razor strops).


Oddly enough, a small number of people spend significant proportion of their working lives using Tool #2 to try to sort out modern etymology by evidence (as opposed to inventing a narrative, which is one of the other major social arts that passes as a social science).


To cut things short:


1. I recommend the use of strop for your device;


2. I acknowledge that some few people may disagree with 1 on the grounds that the circle is not a permanently closed one, just as a snatch block can be opened and closed;


3. 'Lanyard' is an alternative. But no Madman (in the sense of an advertising copy writer from Madison Av) would use it compared to the sounds of 'strop'. A beautiful thing - a soft sliding silky start and a plosive finish, with an r in the middle!


Humans like sounds. A surprising number of words we use are sounds (without meaning). Look at a couple of nautical words we use most every day: pump (seems to have originated in English and spread to other languages - most probably just the sound of the device working) and hoist (a nautical word that most possibly originated among crews of mixed language origins working the North Sea - all research suggests it's just a noise to get workers to synchronize their effort pulling on a halyard).