Unveiling Bullseye Strops for low friction rings

[Seaworthy Lass]

This is how it looks completed:

[estarzinger]

Nice - seems like a good solution.

Now send one to Dock and let him sail upwind in 20kts with it, with a few tacks and a bit of sheet flogging, and we will know if it really works

[Benz]

As far as heating up the rings by friction with poly, rockclimbers routinely run long bits of rope over aluminum carabiners and through aluminum belay devices. Sure, they get hot, but rarely enough to damage the line. Line damage has been known to occur when a long rappel gets out of control (really out of control--think several hundred feet very fast), then the caver, or climber, regained control, stopped, and the heat built up in the belay device (in the case I know of a "rappel rack") melted into the line. But again, I've rappelled very quickly for two hundred feet without damage to my nylon line. So I think not an issue on boats, with their relatively short runs. Still, for long, loaded runs like halyards and mainsheets, you can't beat a ball-bearing block.
Ben

[Dockhead]

Here is what Antal say about it:

Antal Ring what are they for

The upshot is that they say, like the other sources, that the friction is greater. They say that the right choice of rings vs blocks will be different for different applications, but that in general rings are suitable for:

"[V]ang cascades, gennakers' tacks, jibs' sheet leads, lazy jacks, backstays, reefing points and any small deflection angle . . . "

They say that the difference is less when there is a small deflection angle, and that it doesn't matter much for applications where the line mostly runs through not being under load, with the load put on later (jib sheets).

Sounds reasonable to me.

By the way, this looks fantastically useful:

hooks-antal

[weavis]

Originally Posted by estarzinger

Nice - seems like a good solution.

Now send one to Dock and let him sail upwind in 20kts with it, with a few tacks and a bit of sheet flogging, and we will know if it really works

Flog away Dockers.........

[Seaworthy Lass]

Originally Posted by estarzinger

Nice - seems like a good solution.

Now send one to Dock and let him sail upwind in 20kts with it, with a few tacks and a bit of sheet flogging, and we will know if it really works

No need . Our yankee sheet has been put through it and we have just had a day's sailing.
I am much happier personally giving it a trial in case it all goes belly up rather than have someone else use it and have problems.
So far so good .

It was is a bad location for a low friction ring, but I wanted to apply a decent load on the Diamond strop. The yankee sheet had an appalling deflection angle, so at high loads with old poly line the friction was not good. It as still workable though. I will move it forward of the winch next time we sail, which will fix that. I will also try and remember to look at alu temps next time with an IR thermometer.

The strop itself handled itself superbly, even with shock loads. It looked "happy". No nasty cow hitch needed either. I think this Diamond strop is a little gem!

I have a zillion more ideas. My mind is buzzing with all the possibilities. I will post photos from today and my other ideas when we get a better internet connection. The signal is absolutely pathetic at this anchorage.

SWL

[estarzinger]

Originally Posted by Dockhead

They say that the difference is less when there is a small deflection angle, and that it doesn't matter much for applications where the line mostly runs through not being under load,

Agreed . . . And fwiw the test numbers I posted above were for a "worst use" case - 180 degree deflection and decent size load. The frictional differences decline generally linearly with both factors.

That antal hook is interesting - hard toggle, and that same "half hitch whipping" they use on their ring strops, and I guess a sliding piece (metal?) to lock the loop on the toggle, and covered rather than bare dyneema (for anti-chafe?).

[Seaworthy Lass]

The Diamond Short Strop in action. I initially connected another soft shackle as a "safety line", so that is the extra dyneema seen here:

[Seaworthy Lass]

The strop looked like it was behaving well, so when conditions eased the extra soft shackle was removed for the photo:

[Dockhead]

Originally Posted by Seaworthy Lass

The strop looked like it was behaving well, so when conditions eased the extra soft shackle was removed for the photo:

Looking very good!! I will be trying one or two of these

Although I must say that I am pleased with your lacing. I was just on the foredeck and inspected my twings, and you can see that they are stable and happy. There's almost no throat angle so minimal stress. And the ring is nicely cossetted. I think this is also a very good formula

[Seaworthy Lass]

Originally Posted by Dockhead

Looking very good!! I will be trying one or two of these

Although I must say that I am pleased with your lacing. I was just on the foredeck and inspected my twings, and you can see that they are stable and happy. There's almost no throat angle so minimal stress. And the ring is nicely cossetted. I think this is also a very good formula

I am really pleased the lacing is working well.

The attempt to seduce you with the Diamond strop is obviously not working well, so I need to try harder . If I make it a little longer and can bury the tails it will be quite a bit stronger than your loop if made in the same thickness of dyneema. Otherwise, given the cow hitch needs to be used with a loop, as above it is probably similar.

Evans is this correct?

Three other advantages: it is shorter and there is no risk of lacing chafing and it can be undone without pulling out the line (although not taken off completely).

SWL

[Seaworthy Lass]

The Diamond Short Strop after its first workout.
Close up shot under light load shows how it looked at the end of the sail:

[Seaworthy Lass]

I was looking at a few shots of low friction rings in use and found a pair lashed together in a photo Dockhead took on a racing Swan recently.

This is a close up:




It must be very difficult to distribute the load evenly with lashing like this, weakening the system.

The Bullseye weave can be used in this application as well.

Make a loop and twirl it around two rings to join them very snuggly together. Here I used 4 mm dyneema end to end spliced with a 72x line diameter bury tapered over the last quarter of the bury.
Predicted breaking load of this is a whopping 8000 kg! if the line strength is 2000 kg for the 4mm dyneema used.

EDITED TO ADD:
I have a better grasp now of how system strength can reduce in situations like this, so the original estimate of 8000kg I made above is incorrect. Losses in strength will occur for the reasons listed below. I think these losses are not cumulative, so the biggest one simply overrides the rest.

1. Although the throat angle here does not create any "peeling" force (no side load at the crossing), the angle of deviation of the line from the primary angle of pull will reduce strength.
The formula I have come up with for system strength efficiency due to this
= cos (throat angle / 2) x 100%.
The throat angle you would use is the greatest one in the system, as this is what will be limiting things.
I put a protractor on the photo and estimated the greatest throat angle. This seems to be around 60°.
So estimated system strength efficiency = cos (60/2) x 100 % = 87%

2. Bending losses will also occur. The diameter of the dyneema (d) compared to the diameter of the portion of the LF ring it is going around (D) need to be taken into account. In the example here the diameter of the line is 4mm and the ring 35mm therefore D/d = 8.75.
From the graph given in Evans's load testing document, the system efficiency is therefore around 83% due to the bend around the ring.

3. Losses in strength will also occur due to compression and bending of the dyneema at the crossings. Evans Starzinger has pointed this out a few times in both this thread and the one on Antal whipping. Also Brion Toss has said:
"Although fantastically strong in tension HM fibers are quite weak in compression. Since knots invariably compress the rope under load, it is clear why knots typically weaken HM rope by at least 70%."
The losses here due to compression are not known, but I think are unlikely to be anything similar to actually knotting the dyneema.

So, if the above is correct (any structural engineers here that could confirm this?), then the system efficiency is being reduced primarily by the bending of the dyneema going around the ring, therefore it would be around 83%.

So system strength here would roughly = 4x 2000 x 83% kg = 6640 kg
Still a whopping amount .


The rings can still be removed, but only with a fair bit of difficulty (bring the rings together, tip one towards the other, pull on one of the loops going around one ring and eventually one loop can be forced over):

DIAMOND TWIN RING STROP:

[Seaworthy Lass]

One advantage of the above join is that it is super quick if you are not planning to take the rings in and out.
In this instance, I don't think there is any need to lock stitch the splice, as I doubt it can be shaken apart. A simple constrictor knot where the buries start will hold the buries in place until the Diamond pattern is woven.

Big bonus in my book .

SWL

[Seaworthy Lass]

I have been doodling thinking about what we should do with our new system for headsail sheet controls. Dockhead, thanks for the photo below. It us nice to have a base to start from.

A few comments:
The stacked rings on the sheet concern me with chafe issues. They could just be connected with soft shackles couldn't they?

The lower two rings could be connected to the pad eyes with soft shackles too.
They would work a fair bit better than loop strops. Using the same diameter Dyneema, soft shackles are significantly stronger than the loop strops if you use Evans's "Overhand/loop stopper" or a button stopper, both with buried legs. They are shorter than the loop strops as well, which may or may not be helpful.

The line to control the barberhauler could just be spliced to the ring, as you have done for the ring control line. If the line is too old to splice, then use a Diamond Short Strop, which opens therefore could be fed through the eye-spice already on the control line. This eliminates the long strop plus soft shackle combo.

No nasty kinking anywhere with cow hitches in the system then. Cow hitches are on par with a tight throat at the low friction ring in terms of stressing and weakening the system and I think need equal consideration.

I am not trying to criticize, just sharing what I would do, as it may help improve your system .

SWL

Note: I know that the two pad eyes distribute the load on the deck, but if you have one strong attachment point, you could put a Diamond Twin Ring Strop (as in the previous post) down there if you wanted/needed a 3:1 purchase on the twing (only one ring needed for 2:1).