Anchor snubber design.

How you size your snubber and what limits you place on its usage are personal decisions. There are no hard and fast rules.

In a big blow I think you will be lucky if the loads fall to zero on your snubbers :( - but they will constantly cycle - and with every wave, every swell, every gust and every veer - your snubbers will be cycled. Additionally the shorter your snubbers the higher the loads they will endure - which is a vote for longer snubbers :)

Noelex has mentioned that, he thinks, longer snubbers will not be useful, 'more is not necessarily better' - he forgets the length of stretch will be the same, or very similar. If your 10m snubber stretches 1m under a certain load your 20m snubber will stretch 500mm - but if you choose 4:1 as your safety factor you are using half your stretch as opposed to all of it.

The closer to a straight run you can develop plus use of turning blocks should minimise the need to use any dyneema - but I'd strongly suggest considering a bridle, which might allow a straighter run for each arm (as they do not need to run through the bow roller).

Thinwater who scribed the PS article you quoted had a number of articles on the subject based on testing. There is the data you quote, above, and there is also copious data on the testing of climbing ropes. This is theoretical testing , ideal conditions. Usage data is thin on the ground (as most people's idea of a snubber is 2m long! Evan Starzinger used climbing rope, do you know how long his snubbers were? Dashew uses lightweight chain (and snubbers) but definition of what he used is not clear (and complicated as most do not use lighter rodes). I offered our experience, actual usage - and true to form had some 'thoughtful' and predictable criticism.

You really need to make your own punt here - fortunately if you get it wrong - its not end of the world!

it will be interesting to hear what you conclude and then later - how it fares.

Jonathan
 
2 snapped snubbers, one arm each at a time only. This was in the days we were neophytes and used the bridle supplied as standard on our cat. The bridle/snubber were about 4m long each side but rubbed on the kicker wire (in lighter winds), the wire that hold the bowsprit down. Both failed where they had suffered abrasion. They failed with noise of a rifle shot.

We then went through the process of adding rubber devices, complete waste of time (and money) and they are heavy for the usefulness they provide.

We then thought a bit more and went to climbing rope, based on Evan Starzinger's suggestion but also moved the securement point to the transom (which many now follow, including Noelex at the last count). We then went to 17m and now 30m - all tried and tested. We have also been through various iterations of attachment devices (including soft shackles) - but that's another can of worms!
 
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Another thought to add to the mix - slow the boat down!

So considering having a look at the feasibility of adding some spare jordan drogue cones to the chain somehow - worst blow I've been in so far was wind gusting 60Kts from all directions so the boat would fly off to the other side of the anchorage , no load on the snubber then lots!

With kinetic energy = mass x velocity squared, if you reduce the speed by 10% then the energy is nearly 20% less, reduce the speed by 20% and energy is down to 64%. Thats a substantial reduction in force if it's possible.
 
GHA said:
So who has snapped a snubber & how did it fail?
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I have snapped quite a few. It is difficult to know the cause.

The greatest correlation seems the length of time the snubber is used in strong wind. Say more than 5-6 nights in strong wind (say 40 knots+) and the chance of subsequent failure in the next strong wind becomes greater.

It has been suggested the great elasticity of nylon fibres together with salt crystals inside the rope causes the fibres to rub together and chafe internally. Others have suggested there is some internal heating of the fibres which weakens them. I have no idea if these mechanisms are plausible, but In practical terms I am suspicious of nylon snubbers that have been worked hard, even if they look fine.

I have met other cruisers that have experienced similar problems and others that have used the same snubber for many years.

Perhaps the combination of a large anchor with relatively thin chain is a factor making the snubber work harder in my case? Perhaps the nylon has been poor quality? There are a lot of possibilities with no definitive answers.
 
GHA said:
Another thought to add to the mix - slow the boat down!

So considering having a look at the feasibility of adding some spare jordan drogue cones to the chain somehow - worst blow I've been in so far was wind gusting 60Kts from all directions so the boat would fly off to the other side of the anchorage , no load on the snubber then lots!

With kinetic energy = mass x velocity squared, if you reduce the speed by 10% then the energy is nearly 20% less, reduce the speed by 20% and energy is down to 64%. Thats a substantial reduction in force if it's possible.
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I toyed with hanging a stainless steel bucket off the bow, but never got around to it.

The RN used to hang a spare anchor off the bow so that it simply dragged across the seabed, have not tried that either!

We had the same situation you did, sudden bullets at 180 degree directions - we set 2 anchors and tied to a tree, the other yacht tied to 2 trees and had one anchor. Shore lines are good as can be 2 anchors!
 
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GHA said:
Another thought to add to the mix - slow the boat down!

So considering having a look at the feasibility of adding some spare jordan drogue cones to the chain somehow - worst blow I've been in so far was wind gusting 60Kts from all directions so the boat would fly off to the other side of the anchorage , no load on the snubber then lots! ...
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Have a think about the other end too, I've tried buckets off the bow which had little effect and I find it difficult to see that a bridle where the panamas are about 24" apart will make much difference (but I've not tried it so...).

One of the things I intend to make, with the boat in the UK for a bit, is a v-twin riding sail. See http://www.ybw.com/forums/showthread.php?349354-Banging-on-again and in krusty's (sadly no longer with us) profile, http://www.ybw.com/forums/album.php?albumid=212
 
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noelex said:
I have snapped quite a few. It is difficult to know the cause.

The greatest correlation seems the length of time the snubber is used in strong wind. Say more than 5-6 nights in strong wind (say 40 knots+) and the chance of subsequent failure in the next strong wind becomes greater.

It has been suggested the great elasticity of nylon fibres together with salt crystals inside the rope causes the fibres to rub together and chafe internally. Others have suggested there is some internal heating of the fibres which weakens them. I have no idea if these mechanisms are plausible, but In practical terms I am suspicious of nylon snubbers that have been worked hard, even if they look fine.

I have met other cruisers that have experienced similar problems and others that have used the same snubber for many years.

Perhaps the combination of a large anchor with relatively thin chain is a factor making the snubber work harder in my case? Perhaps the nylon has been poor quality? There are a lot of possibilities with no definitive answers.
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I interviewed a bunch, correlated non-chafe failures to a formula, and it became quite clear that shorter snubbers (<20 feet) and too thin lines were the cause. The engineering is not that complex, but the rope has to be long enough to absorb a wave. This generally means at least 35' long and about one size thinner than the fiber rode that would be specified for the boat (1-2 sizes for catamaran bridles, but still only one size for mono, since they single leg load more often). In this way the working load is only about 10% of BS at 50 knots, which they can endure for a long time. This also assumes you are not anchored in breaking waves (very shallow water).

Internal heating is provably, mathamatically, pure myth in this application. The amount of energy generated vs. energy dissipation rates in smaller ropes make that impossible. However, a rope that breaks will appear melted, because of the huge local energy release in nylon at failure. If a new rope is pulled to failure, slowly, in the lab, the ends will fuse. That this often happens under chafe gear is likewise no surprise; the chafe gear is where the rope is bent over an edge. A classic case of leaping to an obvious, but wrong, conclusion. There is one obvious exception. if the rope was loaded well past the safe wll (about 10-15% BS) to 30-50% BS i will begin to heat. However, it was going to fail within a few thousand cycles due to fatigue anyway, so it is again, not certain, heating made any difference. The critical thing is to look at nylon fatigue limit data--no mater what the vendors say, you can't go beyond ~ 10-15% BS and get 100,000 cycles. They don't tell you that.

In general, my testing showed that the snubbing force from yawing was generally no greater than the highest gust or wave, because they don't happen at the same time. Of course, if the boat is galloping all over the place you need to fix that before you pull the anchor out or give your neighbors a heart attack. Yawing can be very serious and reduced anchor holding considerably. Take the dingy off the fore deck, add a drogue at the bridle apex, or consider a hamerlock.
 
This is my 15 th year of living on the hook and I have yet to snap my snubber line despite having seen my share of tropical squalls and storms..

Which means that either I am over size on my snubber or you guys that break them are undersize.

I usually have the snubber line running over a bow roller which helps cut down on chafe. It is also reduces the amount of creaking.
 
Tend to agree with TQA in that my snubber is now three years old, has sat out most nights at anchor through the summers, including some interesting winds. It's two legged, each leg is 16mm three strand generic nylon rope and has an eyesplice at each end of the leg. One eye splice goes over the forward cleat and out through the fairlead then on to a swivel and chain hook. Overall length is about 10 metres. Takes the snatch out in a blow and is only now showing any signs of wear and not much at that. However, the rope is cheap so a new, probably longer one will be in place next year.
 
Neeves said:
We then went through the process of adding rubber devices, complete waste of time (and money) and they are heavy for the usefulness they provide.
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I'm curious about this - why did the rubber snubbers not work? Apart from the ends tearing out on the badly designed ones, they worked quite well in marina mooring situations with swell and are commonly seen on boats moored permanently on swinging moorings. I was going to add one to our shortish nylon snubber next to try it out, but perhaps there's some obvious reason why it won't work that I'm missing?
 
Yngmar said:
I'm curious about this - why did the rubber snubbers not work? Apart from the ends tearing out on the badly designed ones, they worked quite well in marina mooring situations with swell and are commonly seen on boats moored permanently on swinging moorings. I was going to add one to our shortish nylon snubber next to try it out, but perhaps there's some obvious reason why it won't work that I'm missing?
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The normal ones, cfr Trelleborg, Forsheda etc, will stretch to their maximum with a relatively low load, a couple of hundred kgf at most, while the guys above are talking about tons.
I had one, even two on series, indeed in strong conditions they do not add any significant elasticity.

May I add, the fact that so many people are confident in their snubbing systems, which are often very different from each other (length, material, usage time, etc etc) imho shows that some common sense -whatever it is- can provide excess cover for 99% of anchorages. Otherwise do not believe forum. In the remaining epsilon% of situations one is at mercy of people whose anchors do not hold and are crashing into your boat, probably they did not snub correctly? :rolleyes:
 
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Roberto said:
The normal ones, cfr Trelleborg, Forsheda etc, will stretch to their maximum with a relatively low load, a couple of hundred kgf at most, while the guys above are talking about tons.
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Exactly

I tested a Forsheda one (like a dog bone) and a Shockle. If you set them up as instructed, with 3 or 4 turns round the Forsheda device (or the loop of spare chain for the Shackle) then they absorb the same amount of energy as 2m of the nylon used in concert, and I know which is cheaper (and lighter). But they have a finite limit, set by the 3 or 4 turns and beyond that you are using the elasticity of the rope or have straightened the chain. You can increase their ability to absorb more shock with extra turns - and then they break.

So - they have a finite limit to shock absorption.

John Knox, of Knox anchor fame, also tested a Forsheda device and came to the exact same conclusions. It might be on the Knox Anchor website.

The rubber devices are useful in a mooring application because they are shorter, for about 400mm of dog bone length they absorb that same amount as 2m of nylon. You could get the same amount of elasticity in nylon - but it would be too thin.

And I see a surprising number still attached to the line but the rubber device is broken.

As has been underlined 10% stretch on nylon is a sensible WLL for a 10m (or I prefer boat length) line, if you want 'more' stretch in terms of metres then have a longer snubber - it will last longer and you can use the system to higher wind speeds (negating the need to have a storm snubber and a means to attach it). If you use much shorter than 10m then there will simply not be sufficient elasticity and if you use a 2-3m length of nylon then you effectively have no elasticity at all.

More is better - ignore the ideas prompted by the need to disagree on principal and without any foundation. Many yachts are equipped with short lengths of chain, sometimes only 10m, and have anything upto 100m of line - which they use as a single anchor rode. They do complain that the line allows them to wander about in light winds - but they never complain the system does not work in strong winds. A long snubber combines the benefit of lots of elasticity whilst still employing all chain - and if you set up such that you can vary snubber length the problem of wandering about disappears. If you commence the snubber at the transom you have yacht length of snubber and the hook can be just under the bow - not dragging on the sea bed where it might fall off (and dragging on the seabed, common on long snubbers commencing at the bow will abrade the snubber).

A boat length snubber will be good upto about 30 knots - beyond that and you will start to exceed the 10% in gusts. So for most people most of the time 10m or boat length is about right (as most people do not anchor and measure 30 knots at the masthead).

GHA's drawing at the outset of the thread is the way to go - but there are lots of refinements to that initial drawing. Much depends on your deck layout (some yachts have fairleads with little sheaves set into the toerail (for mooring lines) but they would be ideal to get the snubber outboard). But consider longer than GHA first proposed (think his initial ideas were based on a 20% stretch), consider working to a WLL 10% stretch (and if you go to 15% it will not matter too much) and think of longer, like double, boat length (ours are almost 3 x boat length and we have a bridle - so 2).

We coil and store the extra snubber in exactly the same way we do headsail sheets, reefing lines (or any other spare cordage).

If there is any friction in your system then try to introduce turning blocks or covers, if you read some of Thinwater's work in PS, or his blog, you will find he has some excellent ideas on covers for snubbers.

http://sail-delmarva.blogspot.com.au/2017/01/the-book-store.html

Indoor rock climbing walls are a good place to try to source retired rope - you should get them for free. You will need to find a high wall to source 30m lengths - it is impossible to sensibly join climbing rope - you need one piece, for a small yacht try to find 8mm rope, for larger yacht 11mm rope.

Jonathan
 
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Neeves said:
Exactly

I tested a Forsheda one (like a dog bone) and a Shockle. If you set them up as instructed, with 3 or 4 turns round the Forsheda device (or the loop of spare chain for the Shackle) then they absorb the same amount of energy as 2m of the nylon used in concert, and I know which is cheaper (and lighter). But they have a finite limit, set by the 3 or 4 turns and beyond that you are using the elasticity of the rope or have straightened the chain. You can increase their ability to absorb more shock with extra turns - and then they break.

So - they have a finite limit to shock absorption.

John Knox, of Knox anchor fame, also tested a Forsheda device and came to the exact same conclusions. It might be on the Knox Anchor website.

The rubber devices are useful in a mooring application because they are shorter, for about 400mm of dog bone length they absorb that same amount as 2m of nylon. You could get the same amount of elasticity in nylon - but it would be too thin.

And I see a surprising number still attached to the line but the rubber device is broken.

As has been underlined 10% stretch on nylon is a sensible WLL for a 10m (or I prefer boat length) line, if you want 'more' stretch in terms of metres then have a longer snubber - it will last longer and you can use the system to higher wind speeds (negating the need to have a storm snubber and a means to attach it). If you use much shorter than 10m then there will simply not be sufficient elasticity and if you use a 2-3m length of nylon then you effectively have no elasticity at all.

More is better - ignore the ideas prompted by the need to disagree on principal and without any foundation. Many yachts are equipped with short lengths of chain, sometimes only 10m, and have anything upto 100m of line - which they use as a single anchor rode. They do complain that the line allows them to wander about in light winds - but they never complain the system does not work in strong winds. A long snubber combines the benefit of lots of elasticity whilst still employing all chain - and if you set up such that you can vary snubber length the problem of wandering about disappears. If you commence the snubber at the transom you have yacht length of snubber and the hook can be just under the bow - not dragging on the sea bed where it might fall off (and dragging on the seabed, common on long snubbers commencing at the bow will abrade the snubber).

A boat length snubber will be good upto about 30 knots - beyond that and you will start to exceed the 10% in gusts. So for most people most of the time 10m or boat length is about right (as most people do not anchor and measure 30 knots at the masthead).

GHA's drawing at the outset of the thread is the way to go - but there are lots of refinements to that initial drawing. Much depends on your deck layout (some yachts have fairleads with little sheaves set into the toerail (for mooring lines) but they would be ideal to get the snubber outboard). But consider longer than GHA first proposed (think his initial ideas were based on a 20% stretch), consider working to a WLL 10% stretch (and if you go to 15% it will not matter too much) and think of longer, like double, boat length (ours are almost 3 x boat length and we have a bridle - so 2).

We coil and store the extra snubber in exactly the same way we do headsail sheets, reefing lines (or any other spare cordage).

If there is any friction in your system then try to introduce turning blocks or covers, if you read some of Thinwater's work in PS, or his blog, you will find he has some excellent ideas on covers for snubbers.

http://sail-delmarva.blogspot.com.au/2017/01/the-book-store.html

Indoor rock climbing walls are a good place to try to source retired rope - you should get them for free. You will need to find a high wall to source 30m lengths - it is impossible to sensibly join climbing rope - you need one piece, for a small yacht try to find 8mm rope, for larger yacht 11mm rope.

Jonathan
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I dont disagree with any of this except rubber snubbers. We have a very oversized rubber snubber in a 9m nylon rope snubber. We do sometimes extend this if we are anchored in strong winds. Our boat is circa 19 ton and we find the rubber snubber useful. The rubber is about 50mm diameter and 600mm long. It takes considerable force to stretch it. The rubber softens the shock loads conciderably. We didnt buy the rubber snubber but were given it and problably would never have purchased one if we hadnt been given it.
 
Geem,

I think we, actually, agree. I never said rubber snubbers were useless - I suggested they were equivalent (and maybe I should have said 'roughly equivalent') to 2m of nylon (if matching the snubber to the recommended nylon size). 2m of extra nylon, from 9m to 11m might give you the same performance as your snubber - that is not useless, its adding 10% elasticity (whether you use rubber or nylon - its an extra 10%). If the rubber snubber is over sized - you will enjoy more elasticity and to higher loads than using one of the 'recommended' size.

Nylon is cheaper and lighter than rubber.

If you have restricted 'length' go for rubber.

But rubber has a finite limit, much lower than the nylon to match the snubber.

Not many rubber snubber devices have a MBS measured in tons!

Its horses for courses.

Short mooring lines, go for rubber.

Free rubber devices, go for it!

Minimalist wallet - go for nylon (and get to your local climbing wall quickly and recycle the longest ropes they have). Its better than the retired ropes going to landfill.
 
Neeves said:
....Minimalist wallet - go for nylon (and get to your local climbing wall quickly and recycle the longest ropes they have). Its better than the retired ropes going to landfill.
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In reading Thinwater's reply (excerpted below), I noted the reference to size in relation to snubber breakage. He suggests one size smaller than the recommended rope rode for the boat. Given my boat is 12.5 metres and cruising all up weight of c. 14 tonnes I reckon around 20mm (3/4ish) rode would be about right. That suggests I should be looking at snubbers in the 16-18mm range, the 11mm leader rope Ive been trying certainly looks on the thin side. So, this is where the OPs link to the stretchy Liros comes in - another job for the winter will be to get some of that in an appropriate size and sort the ends out ready for next season.

I guess the minimalist wallet would blag as much line as they could get to make up several spares if climbing rope were to be on the thin side :)

thinwater said:
I interviewed a bunch, correlated non-chafe failures to a formula, and it became quite clear that shorter snubbers (<20 feet) and too thin lines were the cause. The engineering is not that complex, but the rope has to be long enough to absorb a wave. This generally means at least 35' long and about one size thinner than the fiber rode that would be specified for the boat (1-2 sizes for catamaran bridles, but still only one size for mono, since they single leg load more often). In this way the working load is only about 10% of BS at 50 knots, which they can endure for a long time...
Click to expand...
 
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Maybe think of a longer and thinner snubber - you could then think of leader rope.

You have about 10m to 12m of deck, you could consider 10m beyond the bow (in stronger winds) and 20m when it gets a bit testing. that's a 30m snubber. It will cost you nothing to try it (assuming you can source a free, retired lead climbing rope).

I think Thinwater's suggestion was that Liros' stretchy rope was an illusion - stick with the 10%, accepting it might be 15%.

Its a bit complicated but you could run from the bow to turning block on the transom and secure back on the bow, that's 20m. I don't think it necessary - having a 20m outboard at 40 knots, why not?

Look at Thinwater's suggestions, think outside the box.

Jonathan
 
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.

Is a complicated solution really necessary? As someone else has suggested, on a smaller yacht considerations of space/weight in the bow may suggest a rode of (eg) 40m chain spliced to 40m nylon. With up to 40m (I.e. All chain) deployed use a conventional short snubber, 3 or 4 meters of nylon with chain hook. IN strong or survival conditions you will want more scope so deploy a minimum of 10m of the nylon and you have a storm snubber built right in. If it blows up and you have difficulty retrieving the snubber to let out more rode then just let it go.

- W
 
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