Anchor snub lines

[lw395]

Most anchoring I've done, it would have to be almost flat calm for a 10m snubber to touch the sea bed.
The tree sounds like a good option, provided the wind doesn't shift too much!

From reading around, I think it pays to think about the energy a snubber is dissipating, and how much that is going to heat up the rope.
The power in even quite small waves is considerable in this context.

 

[Delfin]

Most anchoring I've done, it would have to be almost flat calm for a 10m snubber to touch the sea bed.
The tree sounds like a good option, provided the wind doesn't shift too much!

From reading around, I think it pays to think about the energy a snubber is dissipating, and how much that is going to heat up the rope.
The power in even quite small waves is considerable in this context.

You've just made the argument for not using nylon or polyester line inboard on a snubber where it will stay dry and potentially fail internally from heat build up. Cordage like Plasma or Dux don't stretch and so don't fail internally.

 

[Storyline]

@Neeves (et al). Having learnt that octoplait will degrade by repeated stretching and could also fail before it visibly shows to be worn, is it possible to come up with approximate guidance as to when replacement is recommended ? I don't know whether this would be in the form of a guesstimate as in 'replace after 5 seasons' or something more empirical that has been shown by testing ie we know from testing that octoplait weakens by x after y no. of stretches so given a 90% safety factor it should be replaced after x no. of gales.

There is also the question of reduction in performance that may be able to be measured. 100% of potential stretch (run in) when new, reducing to 50% stretch after 100 stretching cycles. Of course it may be that it stays stretchy until the day it fails.

Just an idea for a day or two of play

Edit: I realise this would primarily be of interest to liveaboards but I (only spend 30-40 nights at anchor pa) would like to have some indication when to change.

 

[Delfin]

@Neeves (et al). Having learnt that octoplait will degrade by repeated stretching and could also fail before it visibly shows to be worn, is it possible to come up with approximate guidance as to when replacement is recommended ? I don't know whether this would be in the form of a guesstimate as in 'replace after 5 seasons' or something more empirical that has been shown by testing ie we know from testing that octoplait weakens by x after y no. of stretches so given a 90% safety factor it should be replaced after x no. of gales.

There is also the question of reduction in performance that may be able to be measured. 100% of potential stretch (run in) when new, reducing to 50% stretch after 100 stretching cycles. Of course it may be that it stays stretchy until the day it fails.

Just an idea for a day or two of play

Edit: I realise this would primarily be of interest to liveaboards but I (only spend 30-40 nights at anchor pa) would like to have some indication when to change.

Good question. I'd like to know the same thing.

 

[Storyline]

Good question. I'd like to know the same thing.

Another thought. A snubber is one of the rare things on a boat that is inexpensive and I would be prepared to replace mine a little bit more regularly just to maintain peak performance to produce a comfortable night, never mind ulitmate strength.

 

[Neeves]

In terms of climbing rope there has been work done with regards to cyclic loading. Indoor climbing walls here must retire ropes that have taken a specific number of falls and must retire ropes after a specific period of time (even if no falls have been imposed). But outside of that I'm not aware of any published work.

I am in contact with someone who is trying to develop a technique to do exactly what is being asked - but its not easy. If you can think of a way of sensible and safely cyclic loading nylon of the sizes we use - you will do us all a service. But ideally we need to be able to cyclic load a large number of times with a 500kg load (that's extreme - but presumably people want to know extremes and it will speed up the experiment.

Snubbers are relatively cheap but have a significant role and their lifespan as a snubber will depend on how much they are loaded (recall that the snubber stretches but the 'catenary' works as well). The individual would need to assess 'how' their snubber has been used. A shorter snubber will have a shorter life.

We broke our first bridle within 2 years, it was short (4m) used very frequently, it was simply a normal cat bridle and failed with a noise like gunshot.

I'd be inclined to retire a snubber after a couple of years and then use it as a spring. When you tie the yacht up, properly, you never depend on one line and retired snubbers seem ideal to use when leaving a yacht for a prolonged period as you are using a lot of lines and the loads are low - just use the retired snubber in a less critical position, and/or double it up

Jonathan

 

[Delfin]

Another thought. A snubber is one of the rare things on a boat that is inexpensive and I would be prepared to replace mine a little bit more regularly just to maintain peak performance to produce a comfortable night, never mind ulitmate strength.

I think that is the right approach. For mine, the expensive bits of the sailors thimble and Dux pennant are not going to wear out at the same rate as the nylon line, so I would expect to replace that every couple of years.

 

[Storyline]

We broke our first bridle within 2 years, it was short (4m) used very frequently, it was simply a normal cat bridle and failed with a noise like gunshot.

I think that is the right approach. For mine, the expensive bits of the sailors thimble and Dux pennant are not going to wear out at the same rate as the nylon line, so I would expect to replace that every couple of years.

Somehow I don't think our undersized snubber is going to see it's fifth season

 

[GHA]

I am in contact with someone who is trying to develop a technique to do exactly what is being asked - but its not easy. If you can think of a way of sensible and safely cyclic loading nylon of the sizes we use - you will do us all a service. But ideally we need to be able to cyclic load a large number of times with a 500kg load (that's extreme - but presumably people want to know extremes and it will speed up the experiment.

Pity I gave up employment for sailing or something like that would have been easy and interesting to see up. You could use a programmable chain hoist with a built in load cell. Leave it running for a week with a Web cam to see when the nylon broke.
Unfortunately even if any exist off the shelf in the southern hemisphere it would likely be beyond the budget.
What would be even more interesting would be to run 2 side by side, with one under water.

Going back to Hi tech rope, a friend did a line replacement on a winch system in some seaward type place, afterwards they run the winches nonstop a few days to check all is well. He deliberately ran one line (tech 12) over a sharp edge with some sandbags for a weekend afterwards "wouldn't hang me washing off it" was the comment but when the damaged bit was tested it still held more than an equivalent bit of steel wire rope before breaking. Details are sketchy but it is tough strong stuff.

 

[Neeves]

Not being in the industry I had no idea you could have programmable chain hoists But my colleague is in America, we are an international lot - you have no idea the fun and games we have with metric and Imperial units (though they probably disdain from calling them 'Imperial'), spelling and words with completely different meanings. But apparently American engineers are educated on both systems - its the reading public we need to accommodate.

I have the chain hoist and the load cell, but I'm the 'programme' and power (limited).

Part of the test protocol is to look at abrasion.

Keep ideas flowing

Jonathan

 

[lw395]

You've just made the argument for not using nylon or polyester line inboard on a snubber where it will stay dry and potentially fail internally from heat build up. Cordage like Plasma or Dux don't stretch and so don't fail internally.

The heat build up in polyester will be much less than nylon.
Heat=work=force x distance.
I agree the nylon wants to be in the water.
What is the heat build up going to be in your rubber dog bone?
Heat is not the only failure mechanism.
Internal chafing due to salt can be another significant one. Fatigue due to movement over a small bend radius is a common killer of string in dinghies.
While I accept your view that a snubber is a disposable item that you accept replacing, I prefer not to replace it during one instance of use, in the same way that I expect my motorbike tyres to comfortably last the journey.
I don't buy into, the 'if it breaks I have a spare, no problem' idea expressed by some posters.
I want to set an anchor and know the gear is good for the duration of a two day blow.

Useful discussion, from my point of view.
Cheers!

 

[Neeves]

PE does not have the elasticity of nylon - one would need to balance having a longer snubber (that will not heat up) against the shorter nylon for the same 'stretch'. You want the 'stretch' to absorb the kinetic energy of the moving yacht. As with most things its a compromise. I am sure nylon cordage is less strong when wet than when dry.

The idea that an item of sailing equipment should not be checked if severely used and/or regularly is contradictory. Sails are consumables, wet weather gear consumables, deck shoes consumables - the idea that a snubber is not to be considered in the same was as other consumables lacks logic.

Even anchor chain is a consumable (the galvanising does not last forever and it can sometime be more expensive to regal than buy new). So some items last a very long time, others - shorter.

We all check our sails, we check our rigging and some replace worn or not to a schedule - why not check a snubber - rock climbers check climbing rope why one earth would we not check a snubber. Artificial climbing wall operators retire climbing rope to a strict schedule (whether they have taken a fall or not). Do people not check harnesses and bosuns chairs and discard them at the first sign of wear - of course they should. I'm light and do lots of mast work (voluntarily) for others - but I'll not go aloft unless its my own harness (I do not like bosuns chairs).

The idea that snubbers are not a consumable and to be treated the same way as other marine consumables suggests we should not check them, because they should last forever. They should last years (or a couple) - but will not last forever and checking them regularly seems wise?

Jonathan

 

[Storyline]

This is stating the obvious but presumably one of the advantages of a longer snubber is that it will stretch less than a short one hence having increased longevity. I know our short one will go to what appears to be full stretch many times when we veer in a gale but maybe even a longer one will also reach maximum stretch - will find out next year

 

[Delfin]

This is stating the obvious but presumably one of the advantages of a longer snubber is that it will stretch less than a short one hence having increased longevity. I know our short one will go to what appears to be full stretch many times when we veer in a gale but maybe even a longer one will also reach maximum stretch - will find out next year

I'm not sure that is true that a longer line would stretch less. For a given force, say enough to stretch the line 10%, a 30' line would stretch 3' and a 15' 1.5'. For any given inch of the line, would not the stretch be the same regardless of the length of the line?

 

[GHA]

This is stating the obvious but presumably one of the advantages of a longer snubber is that it will stretch less than a short one hence having increased longevity. I know our short one will go to what appears to be full stretch many times when we veer in a gale but maybe even a longer one will also reach maximum stretch - will find out next year

Which is probably why we don't all use 1' snubbers as the overall elongation of a longer one is more the boat slows over a longer distance, so the force down the snubber(and on the anchor) is less.

Probably.

 

[lw395]

PE does not have the elasticity of nylon - one would need to balance having a longer snubber (that will not heat up) against the shorter nylon for the same 'stretch'. You want the 'stretch' to absorb the kinetic energy of the moving yacht. As with most things its a compromise. I am sure nylon cordage is less strong when wet than when dry.

The idea that an item of sailing equipment should not be checked if severely used and/or regularly is contradictory. Sails are consumables, wet weather gear consumables, deck shoes consumables - the idea that a snubber is not to be considered in the same was as other consumables lacks logic.

Even anchor chain is a consumable (the galvanising does not last forever and it can sometime be more expensive to regal than buy new). So some items last a very long time, others - shorter.

We all check our sails, we check our rigging and some replace worn or not to a schedule - why not check a snubber - rock climbers check climbing rope why one earth would we not check a snubber. Artificial climbing wall operators retire climbing rope to a strict schedule (whether they have taken a fall or not). Do people not check harnesses and bosuns chairs and discard them at the first sign of wear - of course they should. I'm light and do lots of mast work (voluntarily) for others - but I'll not go aloft unless its my own harness (I do not like bosuns chairs).

The idea that snubbers are not a consumable and to be treated the same way as other marine consumables suggests we should not check them, because they should last forever. They should last years (or a couple) - but will not last forever and checking them regularly seems wise?

Jonathan

Sure we check stuff.
But we expect it to last a reasonable period of the expected use.
My point was I'm looking for something that can reasonably be expected to function through 24-48 hours of the conditions it is designed for.
Not that onerous a demand really, I expect my swinging mooring to survive a week of gales between attention.

By the way, it's not strictly the elasticity that absorbs energy.

 

[LadyInBed]

I realise this would primarily be of interest to liveaboards but I (only spend 30-40 nights at anchor pa) would like to have some indication when to change.

As you probably only anchor in conditions where you never put the snubber under any real strain, probably never!

 

[Neeves]

Sure we check stuff.
But we expect it to last a reasonable period of the expected use.
My point was I'm looking for something that can reasonably be expected to function through 24-48 hours of the conditions it is designed for.
Not that onerous a demand really, I expect my swinging mooring to survive a week of gales between attention.

By the way, it's not strictly the elasticity that absorbs energy.

If you have the right sized snubber, its both long enough and the correct diameter and you ensure that in places of possible wear, say where it runs over the bow roller or through a fairlead it will then last for years. If its 6mm diameter it will not last long as it might stretch to near it maximum and if its 24mm in diameter it will simply not absorb any energy (unless your yacht weighs in at 40t - I guess). So for a 40' x 10t yacht a 12mm x 10m length of multipliait should last a couple of years (and might last longer) and will not need replacing after a 2 days blow. The replacement is a bit like replacing an oil filter - the old filter would probably last another 50 hours, but you replace it anyway and you change the anodes on your yacht when you slip, even though they have 3 months more life.

If you read Delfin's post you will note he has a snubber designed for lighter winds and a heavier one designed for stronger winds. A bit like carrying a storm sail. Horses for courses.

Jonathan

 

[Storyline]

As you probably only anchor in conditions where you never put the snubber under any real strain, probably never!

It depends what you mean by real strain. To my eyes, the octolplait seems fully stretched at times in high winds. I cannot conceive that it can get any significantly longer without snapping !

 

[Neeves]

It depends what you mean by real strain. To my eyes, the octolplait seems fully stretched at times in high winds. I cannot conceive that it can get any significantly longer without snapping !

I suspect it depends on which octaplait, and no-one has tested different suppliers of octaplait (or I have not seen anything), but it should stretch when new about 30%-35% before it snaps. I have seen some data from Yale suggesting their nylon Octaplait (or it might have been a braid) will stretch to 40% though no-one else who manufactures suggests anything over about 35% (unless its climbing rope). (Manufacturers data can be contradictory and/or confusing) For a 10 or 12mm piece of cordage if you are at that level of stretch, 30%, you should be using a thicker cordage - I'd be aiming for 15% (Liros quote 20% working stretch for their 3 strand). Again depends on construction and supplier but a 12mm line will have a breaking strength of, maybe, just under 3t (and 14mm 4t) - so to stretch 15%-20% - suggests really high loads (elongation vs load is not linear). To put in context a 8mm G3 chain has a WLL of 0.8t and a breaking load of about 3.2t (and your shackles etc should be rated similarly).

But recall, your snubber will stretch and the chain lose its catenary 'together' - its not all on the snubber (again I have seen no work and the maths looks quite complex, or too complex for 5 minutes on a Forum thread).

if you run your snubber down the deck its easy to measure stretch, not sure how you do it when the snubber is all outboard (a long tape measure and a dinghy does not seem appropriate in 35 knots )

Jonathan