Do ropes degrade over time?

Aeolus

Aeolus

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Am thinking of making a Jordan Series Drogue. Ideally I'll never have to use it and it will stay below decks, in the dark and will never be exposed to stress or the elements.

How many years will it remain viable? Do polyester double braid ropes degrade over time? If I need to deploy it in 15 years time, will the rope be as strong as when bought?
 
I've only heard of UV degradation, which won't occur of course if your drogue is kept in the dark. Haven't heard that polyester degrades with time (although most things do, to some extent)
 
There was a suspicion a few years ago that nylon climbing ropes would degrade, even if kept in the dark, so the organisation I worked for would not use stock any older than that. That ruling was relaxed to 7 years until further research was finished.
I don't know the current position regarding nylon, but we all know of polyester sheets and halyards that have been in use for donkeys years.
Personally I wouldn't have a problem using a drogue line that has been well-kept.

NB There is a school of thought that the BS of the rope should be approaching the displacement of the boat, considering a max possible stress on the rope. What are you considering?
 
The web sites I've looked at suggest 5/8" (16mm) double braid for boats up to 10,000lb. The Ace website states nylon (16mm - 10,000 lbs BS, according to one web site, 15,000lbs according to another) and the Sailrite website doesn't say what material but also recommends 5/8". Marlow shows 16mm polyester to have a BS of over 15,500lbs.

I was wondering whether something like dockline might be better - I would guess that some stretch would be beneficial. 14mm dockline has a BS of over 13,700lbs and 12mm is 9100lb which is about the weight of my boat.

But I had heard that nylon can degrade over time and wondered whether polyester has the same problem.
 
Steve Dashew et al have looked into this matter, might be worthwhile to consider what they write:

Quote: "...Within a half an hour of setting their parachute anchor, the rode failed about 20 feet off the bow, where chafe was not an issue. In another situation, the 45-foot Freya was riding to a parachute anchor in a compression zone storm just north of Auckland, New Zealand, when their 3/4-inch three-strand rode failed ten feet off the bow.
In both cases we discussed the chafe protection and attachment points on the boat with the skippers, and looked at the structural capability of the parachute anchors. The inescapable conclusion was that the rodes had failed at somewhere between 45 and 60% of rated strength in tension, with chafe not being an issue.... Further investigation with rope manufacturers revealed several startling facts. First, the rated strength of nylon drops by 15 to 20% when it is wet, as compared to the catalog breaking strengths (which are dry rated). Second, when nylon is repeatedly cycled at a high percentage of its breaking strength, typically above 50%, it generates substantial amounts of internal heat. This internal heat degrades the structural performance of the nylon, by as much as half, and is thought to be a common cause of failure at high loads. This internal heating process is worse when the rope is wet."

Source: http://www.setsail.com/_storefiles/71.pdf
 
Yeap Steve has it pretty right. Internal fibre friction is a killer especially in Polyprop. Nylon loses closer to 10% when wet though, which bring it back pretty much to the same as Polyester.

Take another 15% off for any good splices, more for bad ones.

Nylon isn't as UV resistant as polyester but both should last many years. Talking well made ropes here as some coming out of the east are made from what is called Textured Nylon, which is reject material from the clothing industry also know as 'crap on boats'.

Storing any ropes not being used downstairs is a good idea and will help a lot with longevity.
 
Not sure what you mean by "dockline". AFAIK this just just polyester or nylon made up as a docking line. The only thing I'd add is that I elected to use 18mm multiplait for my (not yet used) parachute anchor and drogue lines since this is much easier to coil and flake, which is an issue when you are talking long lines. (though I don't like multiplait for a dockline as it picks up grit much more easily and seems to get surface damage more easily). I have not seen any research on whether multiplait is more susceptible to heat damage as has been referred to in earlier posts. I'd like to think that the structure made it more likely to release heat, but could argue (equally speculatively) that it may also increase internal friction.
 
thread drift, many years ago in africa, where elf and safety dont live, crane, nylon strop and lifting something too heavy, the line actually melted where it broke, presume the internal friction helped to hasten its end
Stu
 
Thats all very interesting - and a bit worrying.

I use a nylon bridle to a anchor chain hook, to avoid any shock loads on the anchor chain. I let out about 30 feet to allow stretch. However, the amount of % stretch can be quite a lot for that length of line. Is this a bad idea, or should I use a considerably longer line?
 
There was an American study which looked at broken moorings and warps after an east coast hurricane. As mentioned above, a major cause of failure was heat damage to nylon - usually where it went through a fairlead. Calder, I think, suggested that if you used a nylon snubbing line in tough conditions, then a short length of polyester over the fairlead/anchor roller might help prevent failure.

A snubber on the snubber so to speak
 
Melting nylon? Yes, I had a similar experience in Gibraltar, where an offshore earthquake sent atypical swell into the marina at 2am. We had short nylon breast ropes to the dock on stainless steel springs. After the springs gave up on one the substantial shackle elongated. On the other the rope parted in the splice, and looked melted rather than just snapped.
 
When you 'bust' a rope it is very common to get 'glazing' in the break zone. You an see it sometimes when you ease a well loaded rope off a winch for example. You get a area when on close inspection looks to have been melted together or pretty close. Spinning a auto rope to chain winch on the rope can do the same thing as well, if fact that is quite common. Glazing is caused by heat, is bad and means you have lost strength possibly a lot like 50%. It affects the area around the glazed bit as well.

Heat nylon to 350 degrees F odd and you lose 50% of it's strength which doesn't all come back when you cool it. It will melt at 450 F odd. Polyester does the same at about the same temp. Polyprop at only 150 degrees F and at 300F odd it will turn to a liquid.

Polyprop has real nasty fibre friction issues so that's why anyone with any clues would never use is as a dockline or any application that get high cyclic loads. I cringe when I see it used as a mooring head rope or anchor rope on any boat of size. Many boats have come to grief due to the owners saving a few quid by buying PP.

The same thing happens with nylon/polyesters as well but at a lot higher temperature. Luckily both of those don't have as high fibre friction issues as PP. But most ropes have some degree of fibre friction issues.

If you have a bit of nylon (even polyester) running tight alongside or over another piece then put it under big load it is very possible for them to heat up and break one or both in very very quick time. When I mean quick I mean as quick as a knife, yes that fast in a bad situation.

So never use PP (it's bloody evil and only really good for tieing things onto the trailer to take to your boat) and when you use Nylon or Polyester make sure that it is well protected especially where it touches anything. We make quite a few drogue and shute rodes. The real serious lads often run a length of chain as a bridle off the boat and then to the rope. This gets the rope away from cleats, stanchions and so on.

Don't use 'cheap' rope in any possible high load situations. Cheap ropes are good but cheap for a reason i.e lower grade raw product. The high grade products usually have far high Thermal Stability so will take the big loads better and longer.

And just to freak you out a bit more - Load a rope to WLL (usually 20% of break, less when climbing on it) and then 'shock it' or even just give it a real big shock. Basically any sudden shock that puts it above 15% (there abouts) of it's working load limit. Rope is now close to dead. It may look fine but the fibres have been damaged and won't come back. It is highly possible that rope can now fail even if you are back to using it inside it's WLL.

As a FYI - If you want a rope (anything) to stop the fall of 1000kg after dropping 1 metre, you will need to have a break load on that rope (anything) of an absolute minimum of 9000kg... Ouch.
 
Re: Do ropes degrade over time? - shock loading

It is a bit more complex in a fall/shock load situation, when fall factors come into play ( definition ), and coping with those loads is one reason why climbing lead ropes are much more elastic than most of the ropes used in sailing. (On saying that, I use a lot of retired climbing rope for temporary docklines, anchor snubber etc). "Fall factor" loads in sailing could almost never get anywhere near the climbing fall maximum ( - a bit off-thread, but easily achievable with safety lines, and a good reason to use elasticated/energy absorbing climbing gear which is designed for short violent shock loads of fall factor 2, the maximum)

Another issue is recovery time after shock loading - the rope takes up to 30 mins (last recommended figure I heard before climbing again after a fall) to regain its elasticity, and hence its strength. As has been mentioned, wet ropes are less strong, and a rode or drogue line, which is both wet and subjected to high repeated loading with no recovery time, will be significantly weaker than the stated breaking figure - and that is without taking into account heat degradation.
 
Re: Do ropes degrade over time? - shock loading

The main reason climbing ropes are stretchier than most sail is they are nylon and sailings are polyester. Climbing ropes are designed to stretch earlier as well.

Yeap, so they are good for snubbers and so on as you say but then a lot weaker as you can't splice most climbing ropes and knots are nasty.

I don't know if your right about the fall factor though. Big grunty masthead headsail going bad sort of thing, that can be a big bit of shock.

All and every rope on your boat will be weaker than the stated break load and getting weaker by the day. Break loads are found in brand new condition in a lab. Splice it, bent it, knot it, expose it to the elements and it becomes weaker.
 
Re: Do ropes degrade over time? - shock loading

"Fall factor" is quite a specific number. Maximum fall factor is 2 ie length of fall/length of rope, for example when a climber is say 5m above a belay, and falls 10m. There is a bigger "shock" on the system than a climber falling 30m, with 30m of rope out - fall factor = 1.

This could occur on a boat with safety lines, and someone being violently thrown - the fall factor could easily be 2 in then - but I can't envisage another situation where the shock approaches that maximum, except possibly in a fall from a fixed anchor when mast climbing.

When climbing fixed lines and ladders, like the via ferrata in the Alps, climbers use a pair of short leashes, similar to safety lines, but they incorporate shock-absorbing structures eg chain loops with stitching that is designed to break, or a slipping friction device. Falling 2m onto 1m of leash is about the most violent force in any kind of fall, and can cause serious injury even if the system doesn't break. That's one reason why I detest standard safety lines, and have made up my own using climbing materials.
 
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