20mm nylon snubber failure - well not quite.

[Simi 60]

Noticed the 20mm nylon anchor snubber looking a bit weird.
This is the short daily use one, not the rarely used storm snubber.
Slid the protective chafe tube back and found this.
Rope is still clearly in good condition appearance wise, protected from sun and hose has not chafed through.
It's a new one for me, never seen Nylon do this before.

I spliced this one in Feb 2021
Need to replace more often it would seem.

[Pete Meisinger]

It looks like chafing damage right at the end of the chafe guard.

pete

[Mac2]

Could be the chafe guard. It looks leather. My leather chafe guard got hard as a rock with age. The surface was like sandpaper. I wonder if the leather itself caused the abrasion on the rope.

[Simi 60]

Originally Posted by Mac2

Could be the chafe guard. It looks leather. My leather chafe guard got hard as a rock with age. The surface was like sandpaper. I wonder if the leather itself caused the abrasion on the rope.

Chafe guard is clear PVC tube
Never had an issue before.

[Simi 60]

New one made.

[Simi 60]

Originally Posted by Pete Meisinger

It looks like chafing damage right at the end of the chafe guard.

pete

It's only because I slide the chafe guard back to see why the lay of the rope looked weird.

The individual strands seemed dry and damaged, 6 inches either side looked perfectly normal.

I think the roller the snubber goes over creates a localised load point.

[Mako]

Originally Posted by Simi 60

I think the roller the snubber goes over creates a localised load point.

Absolutely. Notch concentration stress. I recall that you're 60+ tons, which can present a big load even on 3/4 inch nylon. Have you experienced numerous strong conditions while anchored since 2021, with lots of wave surge?

On the positive side, the snubber is obviously doing its job of protecting your windlass, and it is sacrificial anyway. Cheap insurance.

[Simi 60]

Originally Posted by Mako

Absolutely. Notch concentration stress. I recall that you're 60+ tons, which can present a big load even on 3/4 inch nylon. Have you experienced numerous strong conditions while anchored since 2021, with lots of wave surge?

Guilty as charged.
Early days of ownership had us going for a longer storm snubber if expecting over 25 knots for any length of time - now it seems 35 has become the new 25.
And, now we have flopper stoppers we have been spending more time in exposed anchorage's - if we are comfortable enough we might as well stay.

On the positive side, the snubber is obviously doing its job of protecting your windlass, and it is sacrificial anyway. Cheap insurance.

Absolutely.
This was the first snubber out of a 300ft roll of new old stock I bought in 2021
A lifetime supply of snubbers for $150.

Still, it was a bit of a surprise to see that hidden behind the hose.

[rslifkin]

If you start to experience a similar failure again, it may be time to up-size the snubber a bit. With larger line you'd need to make it longer to get enough stretch, but the end product wouldn't be loaded as close to its breaking strength, so it would last longer and you'd be less likely to develop a failure like this quickly (meaning more chance to notice the problem before it fails entirely).

[mvweebles]

Simi - couple thoughts to reduce point load over bow roller:

First, guidance for rope rode in storm conditions is to ease-out some line periodically to move the point load. Easier said than done but wonder if that might help?

Second, for docks with a lot of surge, common to see a loop of chain used at the dock cleat connected via shackle to a thimble on the dockline. Any way to safely (and quietly) eliminate line as it comes over the roller?

I guess 18-months of full time use isn't bad, but that line was further gone than I would have liked too

Thanks for sharing.

Peter

[twistedtree]

Is it nylon that heats up and degrades when there is a lot of stretch cycling? Or is that polyethylene? Could that be what degraded to local area?

[Porgy]

I’ve read in a few places and from a couple old salts that using hose or plastic tube for chafe is not good. The abrasion of nylon strands as they are stretched and contract under load is a large contributing factor in chafe. The plastic hose prevents water from cooling and lubricating the line at that point. Just a thought.

[Mako]

That makes sense Porgy, but the age old recommendation is to use fire hose, which has a rubber inner liner.

[Porgy]

My understanding is the age old recommendation for old fire hose was because it was cheap or free not because it was necessarily superior. But folks have different experiences.

[SailorGreg]

Originally Posted by twistedtree

Is it nylon that heats up and degrades when there is a lot of stretch cycling? Or is that polyethylene? Could that be what degraded to local area?

For what it is worth, I think stretchability of a snubber is overrated and very hard to calculate. For a given boat, trying to determine just the right diameter of snubber that will stretch but not degrade or break under various wind and wave loads is next to impossible.
The goal is to avoid shock loads at the limits of swing or bucking at anchor. And those shock loads are only an issue under storm conditions. In normal conditions, the lifting of the chain absorbs any shock loads, not the snubber, so there is no need to select a snubber diameter that provides stretch. And one that stretches under normal conditions will degrade rapidly with any conditions above “ normal”.
The desired strength of a storm snubber can be roughly estimated based on an assumed wind speed and boat displacement, etc. But then, one would want to add a safety factor, erring towards not breaking, which would reduce stretch. Sharp bends and splices would all add to reducing the ultimate strength and would need to be added to the equation. So one might select a storm snubber that will stretch at 50 knots, but what will it do if the winds are 70 knots?
Our boat is around 45 tons and we have 7/16” chain and a 1 1/8” 12 plait snubber. Our snubber runs from the deck to a bow eye and then to the chain via a soft shackle. So about 12’ long. I have gone in the water to watch chain and anchor behavior under various wind and depth conditions.
In 10’ of water with 70’ of chain out ( from the end of the snubber, so 7:1) it takes 30 knots of wind or better to lift the chain completely off the sea bed, and then there is still a fair amount of catenary that absorbs the swing of the boat at anchor, so stretch in the snubber would not be a significant benefit.
Recently we sat through a cold front with 50 knots plus for about 10 minutes. We did swing quite a bit, but the snub at the end of each swing was mild and I doubt we ever stretched the chain taught.
I selected 1 1/8” so that even with bends, splices and wear it is still much stronger than the chain. In a choice between ultimate strength and a little stretch ( but not too much) I go for ultimate strength.

[twistedtree]

Originally Posted by Porgy

My understanding is the age old recommendation for old fire hose was because it was cheap or free not because it was necessarily superior. But folks have different experiences.

I have been using nylon hydraulic house sleeving. It's robust yet flexible, readily available at any hydraulic shop, and reasonably priced.

[Porgy]

“nylon hydraulic house sleeving”

Some of those products look the same as those sold as marine chafing sleeve and- coming as utterly no surprise- considerably cheaper than the “yacht” stuff. Rather than buying by the foot from Defender when I need a piece, I think I’ll throw a spool of it on the boat for whenever I want it.

[rslifkin]

Originally Posted by SailorGreg

For what it is worth, I think stretchability of a snubber is overrated and very hard to calculate. For a given boat, trying to determine just the right diameter of snubber that will stretch but not degrade or break under various wind and wave loads is next to impossible.
The goal is to avoid shock loads at the limits of swing or bucking at anchor. And those shock loads are only an issue under storm conditions. In normal conditions, the lifting of the chain absorbs any shock loads, not the snubber, so there is no need to select a snubber diameter that provides stretch. And one that stretches under normal conditions will degrade rapidly with any conditions above “ normal”.

It's not as hard as a lot of people make it. Size the snubber to be strong and durable enough, then just make it longer until you're getting enough stretch.



And ideally, when you let out extra chain to allow the snubber to stretch, don't over-do it. If you only let the snubber stretch 20 - 25% before the chain goes tight, you're much less likely to have a snubber failure. And if you see the chain going tight, you have an indicator that you're using up all of your available stretch and either need to make the snubber longer or larger.

[twistedtree]

Originally Posted by Porgy

“nylon hydraulic house sleeving”

Some of those products look the same as those sold as marine chafing sleeve and- coming as utterly no surprise- considerably cheaper than the “yacht” stuff. Rather than buying by the foot from Defender when I need a piece, I think I’ll throw a spool of it on the boat for whenever I want it.

I have suspected they are the same.

[Capt Ray]

Here is a pic of my snubber with a rubber shock absorber in-line:

https://shellerina.com/2020/09/21/splicing-8-plait/

I really believe it helps in the job a snubber is supposed to do.