Stealth mode - New Generation Ropes

[Steve_C]

Originally Posted by Seaworthy Lass

Interesting that Samson has selected 21.23° as the throat angle.
By my calculations, at the throat this results in a tearing force of 19.4% of the total load applied.
Is this actually the threshold for matching line strength?
Has there been anything published regarding this?
I am interested in this issue, as it seems to be discussed very little.

Regarding the Colligo thimble, it may be fine if the load is parallel with the face of the timble, but if it is oblique, it looks to me as if it could force the thimble out.

By the way, the tearing force with a throat angle of 30.93° is actually 30% of the force applied. So, for example, if the limit of breaking strength is approached for 8 mm line (approx 6600 kgf), at that stage 2200 kgf is acting on the throat to rear it apart. I may be way off base, but this is instinctively not a figure I am comfortable with. Will a Brummel lock before a long bury survive this? Or the insertion point of a simple long bury splice that looks less resistant to load perpendicular to the line, as half the line diameter is taking the brunt? Or will it have failed long beforehand?

SWL

Due to the captive nature of the Sampson thimble, the actual throat does not necessarily need to be jammed hard up against the thimble. As it is moved out the throat angle is decreased, and even a small decrease could make a big difference.

[Breaking Waves]

Originally Posted by Seaworthy Lass

Interesting that Samson has selected 21.23° as the throat angle. Is this actually the threshold for matching line strength?

Not an expert on this, not at all, but: 10-degree deflection is the normal tested point at which uneven loading among different fiber bundles starts to take place in typical high modulus braided rope construction (note there are a lot of generalizations right there and this does depend on rope construction - specific braiding and fibers). At 10 degrees and less, the rope construction can shift a bit and equalize the loads across its fibers. Above 10 degrees and you start to get point loading on a subset of the fibers. 20 degrees is just 10 degrees deflection for each side - that might be an explanation for this geometry.

However, there is something else going on at a splice throat than just deflection, at least on a bury splice (important to note that I guess most of the 'good' testing that has been done on this has been done on tucked spliced loops and NOT bury loops). There would seem to be some sort of fiber point loading where the one side enters the braid center of the other side. Empirically, seemingly the 10 degrees still allows that point enough braid deformation to spread the load. I don't understand the physics of it, would be interesting to see it computer simulation and see what actually happens. But the empirical results would suggest it 'works ok'.

Has there been anything published regarding this?

I've seen a couple of powerpoint presentations on the topic but I can't find any of them, on the net. I guess there are both liability and competitive reasons to keep rope specific test data out of the public domain. And also I guess the industry has settled into a standard that does not create failures and so has little reason to examine it all that much. A lot of the basic work on all this was done many decades ago with wire rope - it is sitting in hardback manuals on old rigger's shelves. wire rope was 'high modulus' so most of that testing is actually relevant to UHMW - not 100% correct again because of different braiding construction but also not too far out. I've had many pulls done with 3:1 ratios and they have not created a weak point/failure mode. These common geometry high modulus thimbles do work well. But I have not ever experimented across a range of ratios to see what happens - samson definitely has.

By the way, the tearing force with a throat angle of 30.93° is actually 30% of the force applied. So, for example, if the limit of breaking strength is approached for 8 mm line (approx 6600 kgf), at that stage 2200 kgf is acting on the throat to rear it apart. I may be way off base, but this is instinctively not a figure I am comfortable with. Will a Brummel lock before a long bury survive this? Or the insertion point of a simple long bury splice? Or will it have failed long beforehand?

I don't really know. If my theory above is correct (again, I am no expert just guessing at what is happening) then you can really survive almost full line strength tearing at 10 degrees (per side) and below because the line can smush around and spread the load. I strongly doubt anyone has tested a brummel for this - it is just not used, but tuck splices are very commonly used (even more than bury's) and have been tested.

I guess you are doing some simple trigonometry to estimate the orthogonal loading. I'd want to confirm that was correct before relying on it too much - seems right, but I have certainly been wrong and surprised before. In your own domain - how strong are the whippings that are typically used on good commercially made low friction ring strops. That should be relatively easy to estimate and would give you a ballpark to check against your calculation.

sorry I can't be more help.

breaking wave

[thinwater]

Originally Posted by Seaworthy Lass

Interesting that Samson has selected 21.23° as the throat angle....

Samson is one of the few rope companies that tests and reports rope strength with eye splices included, rather than on spools (NER used to do this as well). In a way, it makes sense, since there is generally no stronger way to use a rope.

https://www.youtube.com/watch?v=5c2iyd2Oj_w

https://www.youtube.com/watch?v=DP3Jrhe7ICg

[Breaking Waves]

On the throat question . . . . another angle is to look at sewn splices. They usually fail at the standing end (not the loop end) of the sewing. The tail stitches fail from the standing end. One could experiment with the throat angle to see where what angle causes that to change. But I think it would be a pretty decent angle.

Originally Posted by thinwater

Samson is one of the few rope companies that tests and reports rope strength with eye splices included,

You might know, I thought that European companies did tend to test with loops both ends while American companies historically did not - because of different standards?

[Seaworthy Lass]

Originally Posted by Breaking Waves

....
However, there is something else going on at a splice throat than just deflection, at least on a bury splice (important to note that I guess most of the 'good' testing that has been done on this has been done on tucked spliced loops and NOT bury loops). There would seem to be some sort of fiber point loading where the one side enters the braid center of the other side. Empirically, seemingly the 10 degrees still allows that point enough braid deformation to spread the load. I don't understand the physics of it, would be interesting to see it computer simulation and see what actually happens. But the empirical results would suggest it 'works ok'.

Interesting that “most of the 'good' testing that has been done on this has been done on tucked spliced loops and NOT bury loops”. This is not the type of splicing yachtsmen are usually using for UHMWPE.

It is also interesting that Samson have chosen a 21.23° throat angle for their thimbles, yet recommended in their Rope Users Manual that the throat angle should perferably be 12.7° or less.
I wonder why they have done this if 21.23° is actually adequate?

Originally Posted by Breaking Waves

If my theory above is correct (again, I am no expert just guessing at what is happening) then you can really survive almost full line strength tearing at 10 degrees (per side) and below because the line can smush around and spread the load. I strongly doubt anyone has tested a brummel for this - it is just not used, but tuck splices are very commonly used (even more than bury's) and have been tested.

Well Colligo Marine certainly seem to be using Brummel locks on their thimbles :

[Breaking Waves]

An interesting piece with relevance to the discussion about bridle attachment

https://www.samsonrope.com/docs/defa...rsn=f0eceef6_2

Originally Posted by Seaworthy Lass

Interesting that “most of the 'good' testing that has been done on this has been done on tucked spliced loops and NOT bury loops”. This is not the type of splicing yachtsmen are usually using for UHMWPE.

yes, agreed, but it IS the most common splice used on larger ropes used in commercial applications, where testing is often necessary or required.

It is also interesting that Samson have chosen a 21.23° throat angle for their thimbles, yet recommended in their Rope Users Manual that the throat angle should perferably be 12.7° or less. I wonder why they have done this if 21.23° is actually adequate?

As I said in a post well up thread when this was discussed before, I thought it odd and don't know. 5:1 is just not used very frequently. I suppose it is legally 'preferred when possible' while 3:1 is 'acceptable'.

Well Colligo Marine certainly seem to be using Brummel locks on their thimbles :
Do they have test data available? I was under the impression that they were lets say not an engineering driven outfit - might be wrong. Perhaps the Brummel is good for holding higher 30-degree throat angles. But I am puzzled by why they don't use a more standard and conservative thimble geometry.

breaking wave

[Seaworthy Lass]

Originally Posted by thinwater

Samson is one of the few rope companies that tests and reports rope strength with eye splices included, rather than on spools (NER used to do this as well). In a way, it makes sense, since there is generally no stronger way to use a rope.

Those explosions reinforce my view that it is not a good idea for me to be doing any load testing on board .

All the videos I have seen seem to use large diameter rope. All diameters do not behave in the same manner. Even relatively minor decreases in rope diameter can produce staggering different results when load testing knots.

I wonder if all diameters are measured when tables for spliced MBS are produced, or are results extrapolated? Errors greater than this have been known to occur with test protocols.

Also, when I have seen figures for MBS for spliced rope vs unspliced, of note is that vital conditions are never listed: bend ratio and throat and angle. Both these can affect the MBS dramatically. Those throat angles in the above videos are pretty shallow and bend ratio is high.

SWL

[Seaworthy Lass]

Originally Posted by Breaking Waves

An interesting piece with relevance to the discussion about bridle attachment

https://www.samsonrope.com/docs/defa...rsn=f0eceef6_2

breaking wave

That pesky little cow hitch causing yet more problems .

[fxykty]

Originally Posted by Seaworthy Lass

That pesky little cow hitch causing yet more problems .

Though that was in a messenger/tow line use case where the difference in diameters is extreme. Notice that two of their recommended options supported the girth hitching of the messenger to similar diameter grommet or loop. So girth hitch dresses or not should be OK when similar diameter ropes are joined, according to their recommendations.

[Seaworthy Lass]

Originally Posted by fxykty

Though that was in a messenger/tow line use case where the difference in diameters is extreme. Notice that two of their recommended options supported the girth hitching of the messenger to similar diameter grommet or loop. So girth hitch dresses or not should be OK when similar diameter ropes are joined, according to their recommendations.

Yes, I was teasing . I am known not to be fond of cow hitches.

The diameter they suggest girth hitching the messenger line to is still larger than the messenger line, but the difference is that it is not part of the tow line and is easily and cheaply replacable.

[Juho]

Lots of great information in the posts. Thanks to everyone.

Originally Posted by weavis

Given the sailing ships of old were rope dependent.. what knots did they use?

I liked the heavy duty approach of post #314, with blocks and whippings.

Originally Posted by Breaking Waves

But #1 you simply will not get a 'knot' which retains full strength in the standing part of a rope.

I wonder what the overall strength of the old style connection in post #314 is. The multiple whippings and the block might distribute the load pretty well. (But maybe with "in the standing part" you rule out this kind of double rope arrangements. )

Originally Posted by Seaworthy Lass

The Figure 8 loop was one of the few knots tested that did not slip.

With slippery ropes, I think it is essential in the figure 8 knot that there are two lines that run parallel for a long distance, and when under load, the two lines want to slip in opposite directions. There will be a long contact surface between the lines, with sufficient friction. I think that's a good way to design knots for slippery ropes.

Spliced eye loops if well constructed (long bury with the tail tapered gradually over the last 1/3) give close to line strength if the eye passes around an object greater than or equal to in diameter than the line diameter and if the throat angle of the eye is low.

That sounds like a good rule for this kind of work. Once you make that good long splice, you will have two lines that can share the load (and you can in principle even use 50% strength knots). Are you planning to use a heavier line for the bridle, or would two parallel lines (a loop) of the same rope do? Or are you using a heavier line just to make the diameter larger, to help the spliced loop of the primary drogue line?

Originally Posted by Seaworthy Lass

By the way, the force tearing apart base of the eye (the start of the splice) can be calculated, and it gets extremely high as the throat angle increases, but I have not seen any load testing data on this.

I'd be interested in trying some whipping at the base of the eye (if the angle gets big). That should eliminate some of the forces tearing the loop apart. I'm not sure if the whipping should be made tight or not so much (to better avoid uneven loading of the fibres).

Originally Posted by Breaking Waves

On the throat question . . . . another angle is to look at sewn splices. They usually fail at the standing end (not the loop end) of the sewing.

The stitches must cause some uneven loads. I wonder if the old school whippings would be good in making everything more balanced. Maybe a whipping that covers the stitches and some distance more of the loop. There would be just two parallel ropes at the base of the loop, with no additional tensions due to stitches and ropes diving through each others.

Another random thought. Would a figure 8 knot in the middle of a long spliced loop (made with the two parallel ropes) make the line (= straight segment + spliced loop) stronger or weaker? The angle at the spliced loop base would be 0°, and the figure 8 knot would form a new base for the loop. Maybe ugly (whipping would be prettier), but the spliced part would be protected of any tearing forces and uneven pull of the two sides of the loop. Losing 50% of the strength in the figure 8 knot would not be a problem since there are two lines (200%) to start from.

[Breaking Waves]

Originally Posted by Juho

whippings.

I will just comment that both sewing and whipping are art forms when done correctly. But they require significant experience and knowledge to do properly. The vast majority of DIY's attempting them will produce something which is weaker than a simple knot. It's quite a bit easier for most DIYer to produce strong well designed spliced solutions.

I use sewing when dyneema webbing is the best solution, but I use a bar tack machine which most people would not have access to and I know a few 'clever' ways to design web connections which significantly strengthen them. Most DIYers will not beat a simple water knot.

[thinwater]

Originally Posted by Breaking Waves

I will just comment that both sewing and whipping are art forms when done correctly. But they require significant experience and knowledge to do properly. The vast majority of DIY's attempting them will produce something which is weaker than a simple knot. It's quite a bit easier for most DIYer to produce strong well designed spliced solutions.

I use sewing when dyneema webbing is the best solution, but I use a bar tack machine which most people would not have access to and I know a few 'clever' ways to design web connections which significantly strengthen them. Most DIYers will not beat a simple water knot.

a. A these secret, or will you share them? I know that with nylon, layering has been known since WW II.


b. " (important to note that I guess most of the 'good' testing that has been done on this has been done on tucked spliced loops and NOT bury loops)." Could you post an example? I don't recall seeing testing using braided splices, even in large sizes.

[Dockhead]

Originally Posted by Juho

. . . I'd be interested in trying some whipping at the base of the eye (if the angle gets big). That should eliminate some of the forces tearing the loop apart. I'm not sure if the whipping should be made tight or not so much (to better avoid uneven loading of the fibres).. .

The sheet lead system which I made for my blade jib, when I first acquired that sail some 5 years ago, uses several low friction rings on each side, to create a purchase system for adjustment of the sheet lead as a substitute for a track.


For v1.0 of this system, I made the necessary strops using whipping to bind the legs of the strops together to retain the eye. The whipping kept coming apart, and I couldn't understand it -- at first I thought that I was not tying it correctly.



As usual I discussed the problem with my friends on here, and SWL jumped in and figured it out -- the throat tearing forces were pulling the whipping apart.


So eventually in the course of discussion we came up with a way to weave the whipping so that the legs are not pulled together, or not much, and all those strops which I re-made five years ago with the new weave are still going strong today, after 15,000 miles or whatever of ocean sailing.


But SWL got so fascinated with throat-tearing forces in spliced eyes that she invented her famous Bullseye strop, which is depicted in her avatar, which is a leap forward, which captures the ring without throat tearing at all. I'm waiting for her book on knots and splices and rope theory to come out -- I'll be first in line to buy it.

[Breaking Waves]

Originally Posted by thinwater

>>a. A these secret, or will you share them? I know that with nylon, layering has been >>known since WW II.

sorry, not trying to cryptic, just did not think anyone would be interested. And yes, nothing 'new' or 'secret' here, everything was developed decades ago. And I am certainly not any sort of expert or developer in webbing - just use a few things I picked up from others. But there is not much written on it. I tried to find a useful 'educational' link to share with Juno but did not find anything.

I believe the 'strongest' and most commonly used approach (used I guess in most high load applications) is to design so that you sew 'slings' rather than 'end loops'. This does a number of good things - both balancing and reducing the stitching loads. Less common is the layering you mention - this layering can be concentrated in the sewing area (which is what I think you are referring to in WWII parachute applications) - this is marginally beneficial, or 'full application' (like the multi-strands in a lashing) - this has more significant benefits . I have been told that when you better balance the stitching load with some of these methods that the optimal stitching pattern changes but have to admit I have not educated myself on that and still just use bar tacks


>>b. "I don't recall seeing testing using braided splices, even in large sizes.


In larger sizes, rope constructions are common which simply don't use 'full bury' splices. So basically ALL tests of those ropes would use tuck splices. All the quite common 8 strands ropes are an example (ultrablue-8, quantum-8, proton-8, neutron-8, force-8). They all use a tuck splice (like this: https://www.samsonrope.com/docs/defa...rsn=f907cdc5_2).

In 12 strand hollow core construction, you run into two constraints with the bury splice. #1 some applications will not allow the long length of bury and either a full tuck or a partial bury/tuck (like so: https://www.samsonrope.com/docs/defa...rsn=c0f746b0_2) is used to shorten the splice to fit the application; and #2 even when a full bury is appropriate to both the rope construction and application you end up with a cost trade-off between the extra rope cost of the 45-60x bury (which in say 3" rope might produce a 15' bury in rope costing in round numbers $100/ft) vs the extra labor cost of doing a tuck splice (both tuck and bury are full strength splices). In large (and I mean large by commercial and not yachting standards) that cost balance falls strongly toward tucking.

The resolution is low and I can't be certain but I would have said the orange line video you posted above are tuck splices (at least partially tucks) based on seeing bits of tail sticking out are different points along the splice?. Edit: if you look at the image below I believe you can pretty clearly see the tuck strand pattern where I have put the black arrow. Tensile test beds are in fact one of those applications where for big rope you sometimes just cannot fit two full-length bury's in and have to shorten one up to fit the bed.

breaking wave