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]

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]

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]

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]

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]

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]

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]

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]

“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.

 

[rgano]

Simi, you are doing your proper due diligence in your inspection of our mooring tackle. Well done, sir.

 

[Simi 60]

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).

The 20mm is fine and has served us well in all conditions thrown at us over the past 6 years of full time cruising.

It's us that was the issue
We should not have left the short snubber on in boisterous conditions, we don't usually.
But, now we know it's limit.

We have a short snubber for 95% of our anchoring needs simply because a longer one starts going green when in the water after several days - short one stops at water.

 

[SailorGreg]

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.

I think this approach is much better than relying on stretch in the line. With this, the snubber can be sized stronger than the chain and the dock edge absorbs any shock loads.

 

[Comodave]

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.

This. You want a porous chaffing guard so the line can get wet and cool down.

 

[Simi 60]

This. You want a porous chaffing guard so the line can get wet and cool down.

Where does the water come from?
It's not always raining when it's blowing.

 

[Comodave]

Where does the water come from?
It's not always raining when it's blowing.

Not always but if it is storming it may be raining. But if it is waterproof then no water can get in even if it is raining.

 

[Porgy]

Not always but if it is storming it may be raining. But if it is waterproof then no water can get in even if it is raining.

That, and I could’ve swore I also wrote that plastic hose inhibits the heat escaping but guess my typing fingers weren’t keeping up with my brain.

 

[cafesport]

Simi, How much longer did it measure from original, I’m guessing you exceeded the working load by more than 30 percent. Also what’s the bend radius of your chock? From the photo there are a few different things happening which is why we switched our snubbers from twisted 1” and 3/4” to 5/8” 8 strand plaited nylon. We have also replaced them at least yearly since they are always exposed to the sun or submerged for weeks in the water. Between the critters, salt and uv they get pretty rough by the end of our summers. We use 3 snubbers of known elasticities and an adjustable one which can brace any or all of the others as needed. Our shortest one is set up for winds up to 35 knots and in use lives under water. As the snubbers wear and stretch they get too long to stow in their normal positions on deck so we know exactly when it’s time to make new ones. Stretch is a pretty good warning flag.

SailorGreg, I’ve mentioned it before on here that with sufficient catenary you don’t ever need a snubber….until you do, and that’s why we almost always put ours out. Ours was big and heavy and a bit of a pain to rig so I decided there must be a better solution. I’ve found using smaller stretchier snubbers allows the chain catenary to be available at higher wind loads than you would normally expect to see. A stretchy snubber sized a bit lighter than the chain’s catenary force becomes the first line of defense against chain and anchor snatch loads. We usually anchor with enough chain catenary for 35 knots and our no 1 snubber stretches around 10% at this wind speed. Once the sustained wind exceeds 35 both the catenary and the snubber work side by side until around 50 knots. If we expect greater than 40 knots we start with our number 2 snubber. No 2 stretches 10% at 50 knots but has sufficient length to absorb the waves that come with these winds. We then brace our number 2 with our number 1 so 2 5/8” snubbers one loaded to 10% and the other to 20% and we still aren’t yanking on the chain or anchor.

 

[JP2]

SIMI: We switched from the clear PVC chafe guard to the wire-reinforced version and saw a huge improvement in protection. (9/16 size on 55,000 lbs with chain slotted SS plate)

Also noted previously the heat from friction was with the PVC movement against the hawse hole surface and not so much from the nylon line, internally. So your's looks very unusual from here.

Have also used CHAFE PRO for a 3 ply nylon towline for years. Can't say enough about that product and its longevity. Well worth the price.

 

[Simi 60]

Had the same happen with the storm snubber after a sustained blow for several days a month or so back.

Am experimenting now with
20mm nylon from Sampson post to about a foot behind the roller with a thimble and eye splice
From there and over the roller in Dyneema
Then back to a thimble, eysplice and 20mm nylon in whatever length needed given the weather.

Thinking we can then not worry about the hose cover and the dyneemas superior chafe resistance will hopefully be the end of the problem.