Unveiling Bullseye Strops for low friction rings

[fxykty]

Originally Posted by Seaworthy Lass

PS I have found that when reefing, our mainsail only stacks neatly on one tack, depending on which side the reefing line comes in. I wonder if a seperate LF ring will help this issue.



Fxy, is this why you are using an LF ring in this application?



SWL

Our main tends to flake depending on the tack we’re on when we reef, even though the clew blocks for the first and second reefs are on opposite sides.

The clew ring for the third reef creates a relatively sharp edge for the reef line to turn 150 degrees (straight up from the boom, then back and down to the sheave at the end of the boom). The LFR will provide a much wider edge and hopefully less stress on the reef line at that point, especially as it pants in gusts (reef lines are 14mm double braid polyester - future plan is to replace with 10mm UHMWPE).

[s/v Jedi]

Originally Posted by Dockhead

For halyards, my dream would be to have pieces of single braid with eyes on them which go onto some kind of track with hydraulic or some kind of large mechanical advantage screw thingie, and a TENSION GAUGE. To lower the sail, you release the tension from this gadget, and hook on a separate tail which would be handled with a normal winch and cam clutch. This will also facilitate UNtensioning the halyards when you're not sailing. I need to patent this. The normal way to tension halyards is ridiculous.

Something like this? You can add a pressure gauge...
cars-antal

[Breaking Waves]

^^ yea, the approach of 'parking the halyard' by placing an end loop on a track is pretty common on bigger boats. Here is Harken's approach.

a strain gauge would be the neatest way to measure load . . . but usually, there is a separate cunningham (or similar) which is used to place the final tension on, and not the halyard. The halyard is usually just marked perhaps with high and low tension marks.

[Seaworthy Lass]

Originally Posted by s/v Jedi

Something like this? You can add a pressure gauge...
cars-antal

We have these Antal tracks for both headsails. Halyards are single braid dyneema. I can report this system works extremely well.

[Dockhead]

Originally Posted by Breaking Waves

^^ yea, the approach of 'parking the halyard' by placing an end loop on a track is pretty common on bigger boats. Here is Harken's approach.

a strain gauge would be the neatest way to measure load . . . but usually, there is a separate cunningham (or similar) which is used to place the final tension on, and not the halyard. The halyard is usually just marked perhaps with high and low tension marks.

I guess I'm the only person around who had never heard of these. No patent for me!


Looks like one pin for the halyard, and another pin for the "Cunningham". I guess you could use a "Cunningham" with some kind of strain gauge. Might add some purchase to that as well.

[Breaking Waves]

^^

It is worth looking at halyard locks also.

A touch more complicated than the track parking, but even greater benefits.

Both foresail and mainsail locks available.

[s/v Jedi]

I think the halyard eye goes onto the top post and the lower post is for a small line to tension it into a position where you can engage a pin from the car into the track to lock the car. After that, you remove the small line.

For Cunningham I use a similar small line, tied with a bowline to the gooseneck fitting, then up and through the Cunningham or reefing grommet and down to a mast-mounted winch. This is how I set luff tension. I use the Cunningham as reef no #0 and my reef points are done with the same line.

[Breaking Waves]

Related to both bridles and LFR's. Picture of 'samson emergency towing bridle'.

They use what is essentially a huge LFR to connect tow line to a bridle. This is not a 'pin thimble', but a 'rope deflector' pretty much just like the yachting application.

Two observations - they use a 'tapered whipping' approach to the LFR attachment. And they use the ring to maintain load on both bridle arms while yawing.

[Breaking Waves]

BTW - the Huston guys, on their own initiative, have done a little 'dynamic testing' on your bullseye. They are not finished but the bottom line is that (so far) I would not worry too much about the woven strands dynamically working on each other. They did manage to create damage, but they had to work quite hard - clamp the base of the strop (like cow hitching to deck), 50% load, 60 degree movement angle under that load, 24 hour cycle, and introduced some grit. They managed to produce enough damage to reduce the strength by 25%.

If you don't clamp the base, rather allow it to slide (as in just soft shackle round turn on a smooth tube), then there is pretty much no way to create dynamic damage to the woven strands.

That 'sliding' base does create the theoretical possibility of damage to the strop at the base, where it is typically weakest (only 2 strands rather than 4 at the ring). But it seems practicaly speaking fine so long as the attachment metal is large radius and smooth.

And worst case it seems you can see the damage being created long before it is a real problem. They have (so far) not been able to create 'invisible' damage (like heat or compression damage) without introducing excessive loads.

[Seaworthy Lass]

Originally Posted by Breaking Waves

BTW - the Huston guys, on their own initiative, have done a little 'dynamic testing' on your bullseye. They are not finished but the bottom line is that (so far) I would not worry too much about the woven strands dynamically working on each other. They did manage to create damage, but they had to work quite hard - clamp the base of the strop (like cow hitching to deck), 50% load, 60 degree movement angle under that load, 24 hour cycle, and introduced some grit. They managed to produce enough damage to reduce the strength by 25%.

If you don't clamp the base, rather allow it to slide (as in just soft shackle round turn on a smooth tube), then there is pretty much no way to create dynamic damage to the woven strands.

That 'sliding' base does create the theoretical possibility of damage to the strop at the base, where it is typically weakest (only 2 strands rather than 4 at the ring). But it seems practicaly speaking fine so long as the attachment metal is large radius and smooth.

And worst case it seems you can see the damage being created long before it is a real problem. They have (so far) not been able to create 'invisible' damage (like heat or compression damage) without introducing excessive loads.

Many thanks for organising this.
It is great news that they had to work hard to produce damage!

I have been hesitant to recommend this weave to anyone, as the only testing has been my own limited efforts.

The “sliding” rather than fixed base is provided automatically when the soft shackle version is made. I am a big fan of this rather than the loop version. It is hard to get attachment points that have a diameter greater than line diameter and even the same diameter halves the strength of the loop. Cow hitching a loop reduces the strength even further.

Using the soft shackle version in this application (1:1 bend over a padeye) means you will end up with around 170% of line strength rather than less than 100% for the loop (strength is then limited by the base of the diamond knot). It also uses much less line and is removable and is a neater length.

SWL

[Seaworthy Lass]

Originally Posted by Breaking Waves

......
They have (so far) not been able to create 'invisible' damage (like heat or compression damage) without introducing excessive loads.

I have been mulling over this. I know very little about compression damage, except that UHMWPE is subject to it. When you say this damage is “invisible”, does this mean that the line will simply part without broken fibres or strands? Do you know how much of an issue fatigue is here? eg with long term cyclic load.

Heat damage I have observed. The fibres literally melt and fuse, taking on a glassy appearance and feel (cannot be indented with a fingernail). The base of the diamond stopper where it contacts the eye (and also the inner apex of the eye) is one spot I have seen this occurring, although I have not figured out why. I can see no significant movement there that would generate heat. I have always pre-tensioned the stopper well, so it is certainly not due to the stopper moving under load.

The portion of the strop that goes over the top of a low friction ring has been subject that too, but that is understandable given I have sometimes had line under high load moving through the ring (I know, I know, that is not recommended use for these rings ).

SWL

[Breaking Waves]

Originally Posted by Seaworthy Lass

When you say this damage is “invisible”, does this mean that the line will simply part without broken fibres or strands? Do you know how much of an issue fatigue is here?

Heat damage .... The base of the diamond stopper where it contacts the eye (and also the inner apex of the eye) is one spot I have seen this occurring, although I have not figured out why.

“ invisible” was a bad terminology for me to use. You can see and feel all these types of damage. But I typically see chafe which is highly visible and ugly - like looks ugly from 3 m away. Heat and compression typically needs to be looked at from 30 cm and some finger feel before you realize how ugly it is (or is not).

I am guessing what you are seeing at the base of your shackles is actually compression damage rather than heat. The end result is somewhat similar. In both cases the material becomes less fibrous and more chunky plastic like - one by melting and the other by cold flowing (I think ... but a chemist would know better that I). I’ve seen this in slipping tests, like in pulling triple fishermen to slipping point. The line does heat a bit, but as far as I can measure not enough to cause heat damage, so I guess it is actually compression.

I get over my head rapidly here, but have read papers on the compression properties and believe the compression damage is a kind of molecular buckling. This buckling stress driven by the low bending stiffness of the uhmwpe molecular chains. But that’s as far as I go.

Fatigue and UV damage tend to show up more like mild chafe, you start seeing a lot of fuzz on the surface, broken filaments. In fatigue it is throughout the rope, not just at the surface. In fatigue filaments work over each other and cut each other, basically it is chafing itself. In UV you have an oxidation reaction - which breaks the long molecular chains. There is some debate how deep this can/does penetrate - a couple mm at least.

Regarding these sorts of chemical level damage - I’m just in the “I mostly know what to avoid” stage, rather than really understanding the fundamentals. Which is why I had concerns about your loaded bent weaving. It is something that is generally avoided - the Huston boys had the same initial reaction I had. But in that specific case, (it seems) there is generally not enough movement nor compression to create a significant problem.

The Huston boys would know a bit more about all this, but I guess you would need a rope engineer or chemist at Samson (or other engineering driven mfg) to really find qualified deep knowledge.

[Seaworthy Lass]

Originally Posted by Breaking Waves

“ invisible” was a bad terminology for me to use. You can see and feel all these types of damage. But I typically see chafe which is highly visible and ugly - like looks ugly from 3 m away. Heat and compression typically needs to be looked at from 30 cm and some finger feel before you realize how ugly it is (or is not).

I am guessing what you are seeing at the base of your shackles is actually compression damage rather than heat. The end result is somewhat similar.

I wonder if shock loading at these compression points added to the melting? That would have been occuring. Interestingly, the straight bits of the strop looked otherwise unchanged to the naked eye when I could see melting damage at the stopper base and eye apex.

From load testing results on knots and splices it is clear that UHMWPE does not like to be bent or compressed (even a poorly tapered splice will reduce strength by around 10%). I imagine shock loading and fatigue will affect these points far more than straight stretches.

What I have always liked about this material is that damage can generally be inspected for. Sudden failure without this would not be good.

SWL

[Breaking Waves]

Originally Posted by Seaworthy Lass

I wonder if shock loading at these compression points added to the melting?

shock loading can be quite significant extra load. And applied quickly it can cause more movement and heat than applied slowly. I don’t know if speed would effect compression damage - don’t think much, but not sure.

From load testing results on knots and splices it is clear that UHMWPE does not like to be bent or compressed

no high modulus line likes bends. Dyneema is not especially bad in that regard (eg it’s about what you would expect given its modulus, compared to pbo, Kevlar, etc). It is espically weak in compression, rather more than the other fibers. I have always been a bit surprised that the compression weakness does not show up in real life application testing more - it seems rare to see that as a break cause. It suggests to me that I don’t really understand the compression issue.

What I have always liked about this material is that damage can generally be inspected for. Sudden failure without this would not be good.

what I like is that it is so damn easy to make so damn strong, and is so repeatable. You can almost always ensure the textile is not the weak link, unless you intentionally build a fuse and then you build a quite known and reliable one.

SWL

Breaking wave

[fxykty]

Can compression failure occur because of a tight whipping at the base of the knot? So no whipping or a relatively loose whipping?