What is the working life of a nylon mooring strop [ rope ] used in the tropics?

[TQA]

Having anchored out for many years I now have a mooring. Having just had a night of 40 knots with gusts to 50 I decided to inspect my mooring 'strop' which is one of the three strand nylon mooting lines which came with the boat and the line is now 10 years old. Up until now it has resided in a locker and got very little use.

The strop seems fine with no signs of chafe and no broken strands. [ Yes it does have a back up ]

I had a look on line for the working life of nylon rope and came up with 60 months.

I have another piece of the same rope that is used as an anchor snubber and has racked up about 7 years use and is due for replacement with broken strands.

Being a bit of an E C Jones I will replace the mooring strop sooner than 5 years use.

Is there any perceived wisdom on the safe working life of a 3 strand nylon mooring strop.

 

[Slowtack]

Although very slightly north of the tropics here in Ireland............. My swinging mooring is somewhat exposed to westerlies. I use a ships chain and 22mm nylon main rope mooring with a 16mm nylon bridle from main rope to the bow roller and cleats. . I drop the main rope to the bottom every winter while the boat is ashore and replace that rope, thimble and shackle every 3 years. I remove and store the bridle in fresh water every winter so that embedded salt does not crystallise and harden in the strands. s the bridle is exposed to UV I also replace that every 3 years................So far so good.

 

[Neeves]

A mooring strop is hardly expensive, in facts its really cheap. Because its nylon, you are in the Caribbean and its critical I would replace every 2 years. A problem with nylon is that it fails without any warning and for this reason the US Navy have banned usage, too many serious accidents.

Nylon life is dependent on the number of stretches and percentage of its stretch, so 5% stretch a few times is less degenerative than a few times at 20%. UV is also a factor as is whether the lines is wet (which I guess it is). You cannot know how many times it stretches nor the amount. It depends on the mooring design but the fact it is nylon suggests some of the snatch loads are to be taken by the nylon, so it will stretch. If there is lots of chain on the bottom the chain will take some of the snatch loads - extending the life of the nylon. Consequently the idea of 60 months is a completely arbitrary number and worthless.

The other unknowns are who uses your mooring when you were away, how big was their vessel, what were the conditions - you simply do not know and a 20t yacht on a mooring for a 5t yacht can stress the tackle.

We have had 2 nylon snubbers fail, and they failed without warning with the sound of a rifle shot. But snubbers are not critical, there is the chain (in our case another snubber, its part of a bridle) and the chain has a dyneema chain-lock back up).

You do not need to discard completely and, depends on its state when you retire, you can use as a morning line when you go to fuel up. The other usage is as sacrificial strops that you might put round trees or rocks if you tie to shore - they are then part of a mooring assembly, are sharing load and are really there to keep chafe off the actual mooring line - if you need to abandon for any reason - their loss are not something to cry over. You should get a number of such strops from your mooring line, splice loops in each end. (We get our sacrificial strops from beach combing - and have a number of turns round trees and rocks).

But the short answer! - 2 years

I'm ignorant, what is the reference to E C Jones?

Jonathan

 

[thinwater]

I've tested many types of cordage, chain, and hardware for articles. A few thoughts:

a. All of them break without warning. Really, unless you are watching the load cell, there are no signs that the casual observer would notice. The main difference is that nylon stores energy. That is the reason it is banned from certain applications. I rather doubt the US Navy has banned nylon from all applications, only those where recoil is a specific hazard and the line is over a certain size. I know folks that sell to the US military.

b. I've tested nylon DB and climbing ropes up to 20 years old that were stored indoors, unused. They typically meet new specifications in all ways.

How do you estimate condition? That is a tricky matter, particularly for nylon, which fatigues at loads far below BS. Fragile fibers on the surface are cause for retirement (UV). Stiffening is often a sign of internal damage, though lime build-up can also cause that. Finally, you can estimate the number of impacts (that is how climbing gyms do it), but since we don't know the size of the rope, length of the snubber (this affects the load), or the duration, number, and severity of storms, that would be pointless. The 50 month figure might be reasonable for this, if the boat were anchored most nights and the snubber were sized properly. That is probably the basis of the estimate. The number of cycles and % BS fit fatigue models.

 

[TQA]

A mooring strop is hardly expensive, in facts its really cheap. Because its nylon, you are in the Caribbean and its critical I would replace every 2 years. A problem with nylon is that it fails without any warning and for this reason the US Navy have banned usage, too many serious accidents.

Nylon life is dependent on the number of stretches and percentage of its stretch, so 5% stretch a few times is less degenerative than a few times at 20%. UV is also a factor as is whether the lines is wet (which I guess it is). You cannot know how many times it stretches nor the amount. It depends on the mooring design but the fact it is nylon suggests some of the snatch loads are to be taken by the nylon, so it will stretch. If there is lots of chain on the bottom the chain will take some of the snatch loads - extending the life of the nylon. Consequently the idea of 60 months is a completely arbitrary number and worthless.

The other unknowns are who uses your mooring when you were away, how big was their vessel, what were the conditions - you simply do not know and a 20t yacht on a mooring for a 5t yacht can stress the tackle.

We have had 2 nylon snubbers fail, and they failed without warning with the sound of a rifle shot. But snubbers are not critical, there is the chain (in our case another snubber, its part of a bridle) and the chain has a dyneema chain-lock back up).

You do not need to discard completely and, depends on its state when you retire, you can use as a morning line when you go to fuel up. The other usage is as sacrificial strops that you might put round trees or rocks if you tie to shore - they are then part of a mooring assembly, are sharing load and are really there to keep chafe off the actual mooring line - if you need to abandon for any reason - their loss are not something to cry over. You should get a number of such strops from your mooring line, splice loops in each end. (We get our sacrificial strops from beach combing - and have a number of turns round trees and rocks).

But the short answer! - 2 years

I'm ignorant, what is the reference to E C Jones?

Jonathan

OK 2 years use it is. Thank you for the advice. I did not know about the shock and stretch load wear factors.

BTW E C Jones is that well known pessimist Extra Careful Jones

 

[KellysEye]

One thought could you back the nylon rope with chain and shackles?