Rope on rope chafe

[estarzinger]

Originally Posted by Stumble

The cyclone is bad practice....

Why do you think that?

The splices are full strength.

Interlocking the splices means there is no chafe but they can still be disassembled easily.

There are no pins to come loose and no metal to corrode. Which, according to Boatus insurance claims, are both meaningful causes of mooring failures.

A simple "loop thru loop" causes a 50% reduction in breaking strength because of (1 diameter) bend radius. But this loop interlock increases bend radius, and the strength reduction (vs a thimble) is tested at about 25% reduction. This is no problem because the system, like all dock lines and anchor rodes, is properly sized to handle significant chafe. You will note that they (and I) use a thimble at the very end (where it attaches to the chain) because an interlock is not really practical there.

I would suggest it is "the correct solution" rather than "bad practice".

New England ropes do actually know what they are doing

[sabray]

Another huge benefit is the dyneema is in the chafe zone as it comes aboard. I added an outer piece of braid for added chafe protection. Super redundant and I guess that makes it a even worse design. New England ropes has done a lot of testing. I think its a better design then what I see being used on most moored boats.

[estarzinger]

^^

Yes, I also added a bit of fire hose to the dyneema for chafe protection. . . . Probably not needed but why not.

I did a bit of a survey last summer of New England moorings and was surprised at the lack of adoption of the clear best practices . . . You can see moorings made of almost every conceivable material and design and relatively few of them are "best practice".

[Stumble]

Originally Posted by estarzinger

Why do you think that?

The splices are full strength.

Interlocking the splices means there is no chafe but they can still be disassembled easily.

There are no pins to come loose and no metal to corrode. Which, according to Boatus insurance claims, are both meaningful causes of mooring failures.

A simple "loop thru loop" causes a 50% reduction in breaking strength because of (1 diameter) bend radius. But this loop interlock increases bend radius, and the strength reduction (vs a thimble) is tested at about 25% reduction. This is no problem because the system, like all dock lines and anchor rodes, is properly sized to handle significant chafe. You will note that they (and I) use a thimble at the very end (where it attaches to the chain) because an interlock is not really practical there.

I would suggest it is "the correct solution" rather than "bad practice".

New England ropes do actually know what they are doing

I stand by it being bad practice because it reduces the strength of the line. That 25% is a significant reduction in line strength, and because it occurs in the bite of the eye will be the constant point load on the same area of line.

Like I mentioned in the first post, I don't see this as an issue because they have massively oversized the dyneema anyway, but it is still bad practice. And when I was discussing this with very idea with them the team at NER agreed, which is why the decisions as made to... Massively oversize the line.

Just because something is bad practice doesn't mean that it can't be done safely, but you need to build in significant additional safeguards to do it safely.

Frankly I still think the better option is custom thimble-to-thimble hardware but the price is prohibitive for small order sizes, and there isn't enough demand to make enough parts to drive down the manufacturing costs.

[estarzinger]

Originally Posted by Stumble

I stand by it being bad practice because it reduces the strength of the line. That 25% is a significant reduction in line strength, and because it occurs in the bite of the eye will be the constant point load on the same area of line.

Actually . . . No . . . . Because at the splices the line is essentially doubled (eg at the splice each line has two parts). So at that point the system strength is essentially doubled, and then there is a 25% reduction in the strength due to the bend radius. Net net, the line will in fact not break at the connection point. It is in fact strongest there. It will usually break somewhere near the end of the tail bury in a simple bury splice and somewhere in the splice (where the fibers twist) in a brumel splice.

This was explained to me exactly by the NER engineers (and agreed to by the Samson guys), when I was writing the USSailing/ISAF document on the best practice for proper use and construction of dyneema life lines.

[forsailbyowner]

To address the original question rope on rope friction will chafe much much faster than a rope on smooth surface situation. This should be patently obvious and the reason thimbles are used in the first place. It would seem simply passing your line thru the pennant and attaching to another cleat to allow a sawing motion as the boat sails back and forth would be a situation to be avoided.

[Stumble]

Originally Posted by estarzinger

Actually . . . No . . . . Because at the splices the line is essentially doubled (eg at the splice each line has two parts). So at that point the system strength is essentially doubled, and then there is a 25% reduction in the strength due to the bend radius. Net net, the line will in fact not break at the connection point. It is in fact strongest there. It will usually break somewhere near the end of the tail bury in a simple bury splice and somewhere in the splice (where the fibers twist) in a brumel splice.

This was explained to me exactly by the NER engineers (and agreed to by the Samson guys), when I was writing the USSailing/ISAF document on the best practice for proper use and construction of dyneema life lines.

On a typically testes eye the ideal is to move the breaking point away from the eye or the splice, which for dyneema can be achieved. For dyneema a 12-step taper works very consistently to reduce the stress risers to this point, and is pretty easily managed thanks to its 12 strand construction. Testing by NER and Brion Toss showed this, which is why it's also poor practice to just do a bury splice without a taper, but

However the cyclone is different because in use it results in a crushing of the fibers at the tip of the eye. Experience has shown that dyneema reacts very poorly to this type of crushing (as do most ropes). I haven't seen any testing on the cyclones yet, but I just don't believe that the long term use of them will preserve all of the strength of the line.

This is getting detailed, and I feel a little off topic but...

The reason that the Cyclones were made the way they were is that no one has yet figured out a better way to connect nylon and dyneema lines. Typical rope to rope splices don't work because of the different properties of the two materials, I investigated having some specialty double thimbles made, but they would have run in the hundreds of dollars each until a large enough production run could be achieved to allow for investment casting.

Which leaves the only current way to get the most out of the lines involved to be using bow shackles. Which would work, but for anchoring devices is just not realistic since they also introduce a major problem with banging into the side of the hull, and just don't feel like something that could reasonably sold to the recreational market.

Instead the design was to just go with massively oversized dyneema. With the expectation that a lot of the ultimate strength of the dyneema would be lost because of the way it was attached. However when you start with something so massively oversized a loss of a major percentage of the strength of the line would still be acceptable because of the starting point.In fact if you look at the Cyclones they are designed to loose as much as 80% of their initial strength before they are the same strength as the line they are attached to.

That aside, moving to composite mooring lines provides so many advantages that even knowing they do have a downside I swapped my docklines over years ago. Living in a hurricane prone area my major failure mode for docklines is chaff, and thanks to dyneema jumpers I have seen a major reduction in chaffing damage and an increase in the lifespan of the total package.

As for dyneema lifelines.... Oh the problems 49.2 caused for a few years.

[estarzinger]

If you are interested in dyneema splices, this:

1/8″ Dyneema Break Test Final: Bury Splice vs Brummel Splice | | Chicago Yacht Rigging Inc.Chicago Yacht Rigging Inc.

Is interesting.

The bury beats the brumel by long way.

And even with "proper tapper" it breaks right at the end of the bury.

[estarzinger]

Oh, and just as an interesting aside, if anyone wants to understand this a bit better . . . .

The problem with small bend radius is not crushing the fibers on the inside of the bend. It is that most of the load is transferred to the stretched fibers on the outside the bend. With a high modulus (low stretch) fiber (like spectra) pretty much all the load is transferred to the few fibers on the outside of the bend. So only a small part if the rope is taking most of the load. If/when these outside fibers break, then it just zippers in, with the new 'outside' fibers progressively breaking.

This also happens inside knots, where the rope takes sharp bends around itself.

[Jim Cate]

Originally Posted by estarzinger

Oh, and just as an interesting aside, if anyone wants to understand this a bit better . . . .

The problem with small bend radius is not crushing the fibers on the inside of the bend. It is that most of the load is transferred to the stretched fibers on the outside the bend. With a high modulus (low stretch) fiber (like spectra) pretty much all the load is transferred to the few fibers on the outside of the bend. So only a small part if the rope is taking most of the load. If/when these outside fibers break, then it just zippers in, with the new 'outside' fibers progressively breaking.

This also happens inside knots, where the rope takes sharp bends around itself.

This effect can also be seen when ill-advised folks try to save some money by bending 1x19 wire around thimbles and securing with Nico-press sleeves.
I've seen a few such where the outside strands have fractured and the whole thing is on its way to failure, just as Evans describes in Dyneema structures.

IMO, the Cyclone construction shown looks quite sound, and the doubling of the line in the eye should indeed make up for any weakening... again as Evans has pointed out.

Cheers,

Jim

[sabray]

I think saying its bad practice to use something that is better then much throws people off. Maybe in need of improvement is better.
I have taken to adding chafe to the eyes which seems to support the eye although not as well as a thimble. Basically leather stitched in and then a full whipping. This seems to give added structure. Maybe somewhere it is causing undo harm. Not a bad practice so far I just have no idea.
With snubbers I have had good luck playing with different means. Still I come back to a hard turn in one of the attachment points or abrasive edge of a steel eye. So I have taken to leather chafe and whipping these.
Wish I had a machine to pull test these.
It's very redundant and I think its a good setup. Not really bad practice just unproven and makes sense.
For moorings I hated my doubled set up. Even the chain to the mooring chain with slack and a loaded pendent would wrap over time. With a single 3/4 braid 13000 lb test I think to the 2 14mm dyneema this under wrap rarely occurs. The oversized design had this added benefit .

[Stumble]

Perhaps we are dealing with a terminology issue. For me the phrase 'bad practice' is an indicator that there is something less than optimal in the system. In many cases it may be from not understanding the materials or processes being used, while in others it may be a result of other priorities driving a non-optimal decision in other areas which requires mitigation to overcome. I see the Cyclone as the second, which NER has mitigated by over sizing the line.

Another example of this is with the way most people use spliced eyes in halyards. Here is another example of where best practice for the line would be to use a thimble attached to a shackle. But since weight and travel into the mast head crane is also an issue, people routinely accept reduced lifespan on the slice instead of doing it properly. Of course modern halyards are rarely sized for load particularly with dyneema line, and instead are sized for stretch. Which means that whatever is lost in ultimate strength really doesn't matter since the line will rarely see more than fraction of its breaking strength.

As an example, the tylaska THL-H20 which is specced for up to 5/8 halyards. It has a thimble diameter of 1.5" which would be a little better than 3:1. Which is far smaller than the recommended 8:1. However the MBL on the shackle is only 20,000lbs, while 5/8" Dux has a MBL of ~87,000lbs. In this case the loss of ultimate strength of the line is meaningless since the hardware will explode long before you reach the reduced strength of the line.

[thinwater]

Originally Posted by Stumble

Perhaps we are dealing with a terminology issue. For me the phrase 'bad practice' is an indicator that there is something less than optimal in the system. In many cases it may be from not understanding the materials or processes being used, while in others it may be a result of other priorities driving a non-optimal decision in other areas which requires mitigation to overcome.

Wow. Lots of big words. I'll use short words. I'm an engineer.

This has been studied and those tests can be found on the net:

• 2 eyes cow hitched is stronger than the line. I have test broken lines joined in that manner.
• Long-term chafe tests have been done. Nylon chafes under variable load, until the knot is set. Then chafe stops.
• VERY FEW lines break due to splice or knot errors. They nearly always fail due to chafe, sharp edges, flexing (Kevlar) or crushing.

For mooring lines--the subject at hand--chafe, chafe, chafe... and don't retrieve it under the chain.