Stealth mode - New Generation Ropes

[Seaworthy Lass]

I have just mocked up how I plan to construct the bridle Y junction.

I used 3 mm UHMWPE. I will go for 14mm Acera for the bridle and leader, mainly for chafe protection (this had a MBL almost double compared to the MBS of the original polyester recommended, which is a very comfortable margin)

A loop was spliced using 72 x bury tapered over the last 1/3 and lock stitched using Samson’s instructions with stitching using one strand of the rope. Samson suggest polyester or nylon for the stitching, but I am going with Timm Rope’s recommendations of using UHMWPE for the stitching.

I tried a three fold loop, but didn’t like how it sat. It looked much “neater” with a doubled loop, so will go with this. One bonus of mocking it up first is that design can be tweaked. Looking at it with a fresh eye maybe the loop could be removed from this arrangement. I am now getting a sore head debating all the options.

The two bridle legs and leader are eye spliced directly on the loop with buries and lock stitching as in the loop.

Eye length is generous. I have found nothing specifically written about what tearing forces UHMWPE can handle. Samson have a general recommendation of preferably no greater than a 12.7° throat angle to keep tearing forces acceptable, which I think this equates to a tearing force at the base of the eye splice of 5.6% of the total load applied, but this was not specifically written for UHMWPE.

I can only guess what is actually acceptable. Eye length only needs to be 50 x throat diameter when passing over the two lots of line in the loop to bring the tearing force down to 1%. I am plucking 1% out of thin air, but I need to pick some figure, so don’t crucify me for suggesting this.
Note: this figure is not the same if using two cow hitches on the leader, as the diameter at the apex of the eye is about 3-6x this arrangement.

So for 14 mm Acera, eye length would therefore need to be 700 mm. Probably way overkill, but it uses very little extra line and I see no harm in being generous.

UHMWPE chafe protection will be added to all three eyes and also to the loop in its single state.

I didn’t trial it under heavy load, but recruited my husband to pull on the leader while I hung onto the bridle legs and simulated yawing the “boat” around, roughly keeping the 2.5:1 relationship of bridle length to attachment separation distance. It all looked very good.

I have photographed the set up . It incorporates no knots at all. This has been the bring home message for me - NO KNOTS AT THE Y JUNCTION. I will mull over it and probably leave the loop out. I am comfortable with this arrangement, but warn that cruisers need to make their own judgement call. Much of this is speculative:

[oldbilbo]

I'd agree with much of that. It's not a competition, and the rough notions explored and depicted were not contenders for prizes. They help me, at least, envisage what NOT to bother with.

I feel the first pic is closest to what previous consensus is pointing towards, and envisage that using a softy loop with a max of, say, three turns and in much beefier cordage would be beneficial. The softy loop could - perhaps should - itself be encased in anti-chafe material.

I'm still interested to explore the possibilities of 'lifting strops', for they're commercially available relatively cheaply and are certainly strong enough. The issue of avoiding chafe is agreed, and one type I'll explore further is a continuous loop of multiple internal load-bearing strands wholly clad in anti-chafe material..... but not available/to hand when I was mocking-up ideas.

There are many ready-made arboriculture and lifting industry products, where the manufacture standards are known, which may already be suitable.... such as this example:





Samson Ropes seem to be involved in many of them, and I'm sure 'Thinwater' could tap into his excellent sources for existing knowledge. Perhaps we don't need to re-invent ALL the wheels....

[Seaworthy Lass]

This is how it looks without the loop. Seems to function OK with what little experimenting I have done. This follows the KISS principle, which I like. I am not usually so indecisive, but this issue at the Y junction holds so much uncertainty.

To achieve an arbitrary throat tearing force of 1% of the total load, I think the length of the bridle eyes needs to be 25 x line diameter of the leader. The length of the leader eye needs to be 50 x line diameter of the bridle. If the bridle legs end up on top of each other then 50 x needed for the bridle eyes also. Probably safest to be generous. This requires very little extra line in the scheme of things.

From the photo you can see the shape of the eye and the resulting narrow throat angle for the leader. The bridle eyes are side on and the throat angles not visible, but they are the same in this set up.

I will add chafe protection to all three eyes, but I am guessing chafe won’t be a big issue at this Y junction. The bridle legs are jammed next to each other (or may even slide on top of each other when load is equal on both legs, so they don’t need to move far when the load transfers.

[conachair]

Originally Posted by oldbilbo

There are many ready-made arboriculture and lifting industry products, where the manufacture standards are known, which may already be suitable.... such as this example:

Good idea! Maybe not for the bridles, that length and strength they'd be huge, but maybe worth considering for the attachment between the drogue & bridle. 3 wraps of a 2t swl spanset & a 3.25t shackle would have a lot of strength, provide a decent radius for dyneema and wouldn't mean the bridle legs and drogue would be captive. I've spent decades rigging live events over the years, spansets (like hoover, not the actual thing but trade name that everyone uses to describe a round sling) can take enormous abuse. Radius of the dyneema/spanset junction might be an issue for the spanset, though they do a load of anti chafe as well which might be a way around that.

https://www.spanset.com/uploads/au/0...Chapter_LR.pdf

[Steve_C]

I like the simplicity, and it seems to offer the least amount of problem.

Just thinking "Out-Loud" here, but what if you buried a short part of one eye of one of the bridle legs into the other just where they go thru the loop of the leader. It would create one eye just where it went around the loop. it would have twice the diameter of an individual strand and could even still have chafe protection. It might keep things even more static as the loads switched from one bridle leg to the other. Excuse the crude drawing. I would really have to actually build it to see if it would look like I imagine.

Of course it would be a really short bury and probably not long enough. especially unless it was much larger line.

[Steve_C]

I just tried this with a piece of 5/8 polyester just to try an visualize and I don't think its possible. Just too short a distance before the two legs split.

[Steve_C]

Maybe just get a short section of 24 mm or larger and use that for a short bridle.

With that size you could probably even just tie a figure 8 knot and never really push the limits.

[Steve_C]

I had a little more time this evening and I mocked it up with some single braid polyester that I had. I am 5 hours away from the boat and any good line.

I was concerned about having two bridle loops in the one eye, when the boat yaws and all of the strain is on one eye, it could pull to the front, and then if the strain reverses the one in the back will be trying to move the one in the front in order to get to the end of the eye.

I was trying to envision a way to keep them in the same place regardless of the strain.

With the strain I able to place on this, even constantly alternating the strain from one leg to the other they stay stationary.

[oldbilbo]

I like what emerges from a KISS approach to this, and agree a high priority is to mitigate the potential for chafe damage. Having the bridle and leader-loop components 'oversized' increases bend radius and gives chafe tolerance improvements, and that may be enhanced by fitting at least one layer ( perhaps better with two ) of tubular chafe-guard onto each of the three loops.

I still favour linking the three loops by means of a hefty softy shackle, passed twice or thrice, and also sheathed in anti-chafe tubing. This permits demounting the bridle legs from the leader and the rest, with inspection after use and replacement if warranted.

I'm just not convinced by paring specs to minimums when very substantial material is readily available. One might call it 'defence in depth'.

[Seaworthy Lass]

Originally Posted by Steve_C

Maybe just get a short section of 24 mm or larger and use that for a short bridle.

With that size you could probably even just tie a figure 8 knot and never really push the limits.

Starzinger found that in single braid Dyneema the figure 8 knot only retained 42% of line strength (as opposed to 73% in double braid Dacron).

I think cyclical loading could make this figure worse.

[thinwater]

Originally Posted by Seaworthy Lass

Starzinger found that in single braid Dyneema the figure 8 knot only retained 42% of line strength (as opposed to 73% in double braid Dacron).

I think cyclical loading could make this figure worse.

The problem with high modulus lines is that they are so non-stretch, there is less load sharing around bends.



I worked with Starzinger on chafe as well (I made up samples, we both pull-tested them). We found that chafe damage to UHMPE is often far more damaging than it appears; it is NOT proportional to line diameter if the damage is in a small area, such as if it rubs on something. The loss in strength might be twice what is predicted, similar to knot strnegth. Again, the cause is poor load sharing.

Pretty scary for JSDs. This was also a factor in several UHMPE lifeline failures; more strength was lost than it appeared.


You can test this yourself. Abrade a small area on just one side, as though it rubbed on steering gear, and then break it.

[Seaworthy Lass]

I know enough about the dynamics of what is occurring at the Y junction to know I know abysmally little, but it does’t stop me mulling over the problem. I am in the middle of constructing this drogue in UHMWPE so the issue is not academic.

I had initially assumed (and we all know what that word breaks down to ) that when the load was evenly distributed, unless the legs of the bridle were connected they would sit apart on the eye of the leader. Given the relatively long bridle this is not the case, even using rope 3 mm in diameter. Mocking it up, the bridle legs actually sit jammed next to each other with equal load. So there seems to be very little sliding around on the leader of the eye of the leg of the bridle that is under load as the load shifts, although one eye does “flop” after the load is taken off it, and as Steve points out, one may try and “move” the other out of the way.

Having a bit of a play with the last mock up I can’t really see why the eyes need to be connected or “glued” using cow hitches that clamp on the line. Maybe if one flops around more the shock load at transfer is higher? Is that the issue? Or is simple chafe the concern? Could someone shed some light here?

If they are connected and the drogue starts swivelling, will not a connection of the legs at this point be worse?

If it is a shock load issue at transfer, then in UHMWPE how are the cow hitches (with tight bends and compression issues) that are currently used, going to handle this long term anyway?

I know cow hitches are the current method of attachment of the bridle to the leader and no failures have occurred, but numbers of UHMWPE drogues that have been constructed, let alone used, let alone used with the “worst case” wave that Jordan described, are probably minuscule. UHMWPE does not behave like polyester or nylon.

John Harries (Morgan’s Cloud) has recently commented:

“In fact, I would go a step further and say that the more I learn about all this, the more I think that all series drogues to Jordan’s design should have at least the bridles and the first section made from Spectra/Dyneema.”

So this issue is probably shortly going to be facing lots more cruisers who choose to carry a series drogue.

[Seaworthy Lass]

One other thing I am puzzling over is why are we using minimum breaking strain to select line diameter, not safe working load?

The recent loss of a drogue and resulting pitchpole is inlikely to have occured (even with the Flemish loop) if SWL had been observed.

Edited to add: Maybe when polyester and nylon were the only options, line diameter and weight would have been phenomenal if any attention was oaid to SWL rather tham MBS, maybe making the set up unworkable. In this case you just hoped you never encounted the worst case scenario.

With UHMWPE this is no longer an issue. Why don’t we now select line based on figures for SWL, which is generally taken as 20% of MBS for UHMWPE?

[Ambler]

Originally Posted by oldbilbo

I like what emerges from a KISS approach to this, and agree a high priority is to mitigate the potential for chafe damage. Having the bridle and leader-loop components 'oversized' increases bend radius and gives chafe tolerance improvements, and that may be enhanced by fitting at least one layer ( perhaps better with two ) of tubular chafe-guard onto each of the three loops.

I still favour linking the three loops by means of a hefty softy shackle, passed twice or thrice, and also sheathed in anti-chafe tubing. This permits demounting the bridle legs from the leader and the rest, with inspection after use and replacement if warranted.

I'm just not convinced by paring specs to minimums when very substantial material is readily available. One might call it 'defence in depth'.

I use a big tested Bow shackle to bring both lifting strops together on the bow then the shackle pin is passed through a thimble on the drogue line.
I am interested on your thoughts on that setup. A good friend in southern Tassie, who has deployed hers many times, gave it the tick of approval except for the thimble quality. I am on the hunt for a cast stainless one.
Perhaps resplicing the Spectra cored super yacht braid drogue line with an eye and anti chafe cover would be the go. What do you think?

[s/v Jedi]

I've been contemplating every option presented and think this drawing (I attached it again) from SWL comes closest to the simplest, strongest and most proven setup. I don't think this is an area for experimental knots, splices etc.

That said, It worries me that when all the force is on one leg of the bridle, the other leg could drag all the way up to the throat of the leader splice. Even when you think it would be above water, with waves you can never tell and we must consider this is being violently dragged and whipped through water.

So, I would want an insurance policy and in this case that would simply be a lashing around the legs of the leader splice that keep the two bridle legs nicely in place at all time. Even though there should never be much force on this lashing, I would still use that 1.8mm Spyderline