Anchor snubber design.

G

GHA

Well-Known Member
Joined
26 Jun 2013
Messages
12,552
Location
Hopefully somewhere warm
Visit site
Think this should work ok, any thoughts?

Basically, Dyneema strop around a (very) strong point at the cockpit connects to a length of nylon which runs up the side deck -> into some 12mm dyneema to withstand any chafe through the bow roller -> into another length of nylon attached to the anchor chain with a soft shackle, probably longer than drawn thinking about it.

Not so sure about 10mm for the side deck, maybe a spare in 12mm.

WIll probably need a block as a fairlead to keep the dyneema square to the bow roller. Then no chance of any chafe on the nylon.

I'd go for climbing rope if any climbing wall retired stuff was available round here.

Hard to find nylon as well, so prob this stuff -
https://www.svb24.com/en/liros-handy-elastic-mooring-line.html



GCmzrRE.png



Some numbers here -
https://www.practical-sailor.com/issues/37_63/features/What-is-Ideal-Snubber-Size_11951-1.html
snubber2.jpg
snubber1.jpg


Thoughts? Enhancements?

Ta.
 
Ok more seriously, re chafe problem, I used two lengths of different diameter fire hose: the snubber textile goes through a section of red stiff hose (very stiff and resistant, nothing in common with water hose, one needs a saw to cut it), and is tied to this piece of hose. The diameter of this hose is a few mm above that of the rope.
All this goes inside a second length ot fire hose, but this second length is of the flexible one, the type used in great lengths which folds flat, diameter roughly 10cm. This is fixed to the roller.
When the rope extends, it brings the inner tube with itself (so no friction for the rope) which in turns moves inside the outer hose, if the boat swings it s the outer hose which takes all the friction against the bow roller elements, cheeks etc
Its length can be adjusted to suit different depths, moving the 2-hose chafe protection along the rope takes a second.
Very happy with it.

Addition: I have 10mm chain, I made a few "double" soft shackles of the type indicated by Evans Starzinger (web site seems to be down?), a double 6mm dyneema is the thickest that can go through the inner empty part of a chain ring, and after a few times the braid opens up and it becomes increasingly difficuilt to thread it inside the link, so not sure yet if I ll use that, I have to make a few more tries (and change chain as mine is too rough)

Best luck r
 
Last edited:
Roberto said:
7119.7mm ?
:)
Click to expand...
Schematic :) & lazy cad.

Roberto said:
Ok more seriously, re chafe problem, I used two lengths of different diameter fire hose: the snubber textile goes through a section of red stiff hose (very stiff and resistant, nothing in common with water hose, one needs a saw to cut it), and is tied to this piece of hose. The diameter of this hose is a few mm above that of the rope.
All this goes inside a second length ot fire hose, but this second length is of the flexible one, the type used in great lengths which folds flat, diameter roughly 10cm. This is fixed to the roller.
When the rope extends, it brings the inner tube with itself (so no friction for the rope) which in turns moves inside the outer hose, if the boat swings it s the outer hose which takes all the friction against the bow roller elements, cheeks etc
Its length can be adjusted to suit different depths, moving the 2-hose chafe protection along the rope takes a second.
Very happy with it.
Click to expand...

Don't think chafe will be a problem. Hoping anyway, I just made up a strop from some 12mm D12 max SK99 which was lying around , incredible stuff. Couple winters ago I made some short strops from 5mm D12 & left them going through the fairleads attached to the bow/stern lines & springs. Months of vicious storms in Dartmouth and barely any chafe. Amazingly tough material.

This should have a breaking load at over 20 tonnes...

13pKZyl.png
 
I would have thought that dyneema was not good snubber material as it has limited stretch. You want something like 3 strand nylon. That is what I use and my current piece has had 6-7 years continuous use and will be replaced this year. I use a chain hook and the snubber line runs over a bow roller and back to a cleat. The snubber is cleated off to have about 4 ft over the roller. keeping the hook above the water in calm conditions. I have about 20 ft of snubber on deck and this allows me to have a much longer snubber line and more elasticity in conditions where snatching is a problem.
 
TQA said:
I would have thought that dyneema was not good snubber material as it has limited stretch. You want something like 3 strand nylon. That is what I use and my current piece has had 6-7 years continuous use and will be replaced this year. I use a chain hook and the snubber line runs over a bow roller and back to a cleat. The snubber is cleated off to have about 4 ft over the roller. keeping the hook above the water in calm conditions. I have about 20 ft of snubber on deck and this allows me to have a much longer snubber line and more elasticity in conditions where snatching is a problem.
Click to expand...

It is almost all nylon, the only dyneema is over the bow roller to deal with any chafe.
 
Ive been experimenting with some retired leader rope this summer, it dont half stretch in 40 knots. Had to make the bow roller protection tube about 2 metres long and significantly increase the chain loop. I like the idea of a backup line in case of breakage in the snubber but for my setup I think that needs to go from the chain onto the windlass cleat.
 
TQA said:
You want something like 3 strand nylon. .
Click to expand...

Hmm, not for me: maybe I had three types of badly constructed/unbalanced rope, possible, but I found that all they 3strand ropes twisted a lot when under load, and textile twisting while wrapping chain around itself, give it xk cycles and it s gone..
Not for,me, at least how I use snubbers (long,to very long)

Also, depending on construction, rope is often not isotropic, meaning its elongation is not constant, not the same at all with low loads in %bs: usually a lot higher elongation with low loads, which might suggest using higher dia rope.
Then add the variation of:the mechanical characteristics over time and usage, big question mark: when highly cycled nylon seems to elongate more similarly to polyester, but with lesser mechanical caracteristics (UV exposure, water immersion, etc)
An optimal solution with a given construction of brand new material, may see all its advantages to fade very quickly.
 
GHA,

You are trying to keep the stretch of the snubber within 10% of length. With your length of snubber that's actually not much stretch. As winds increase and you are approaching your 10% limit - what are you going to do? You can exceed the 10% stretch - you will simply reduce snubber life - snubbers should be considered a consumable (so you should have spares).

Options include deploying more chain, but if your snubber is a fixed length you will need to retrieve to the hook, or whatever, deploy more chain then re-attach the hook. An alternative is to have 2 snubbers on one hook, one a normal snubber one a storm snubber - gets a bit fussy. But you would simply bring the storm snubber into play as the everyday snubber (good to 35 knots) is obviously going to be stressed (and let both work together or simply ease off the everyday snubber).

We are using 11mm leader rope. Our arrangement is much as you indicate except ours is a bridle, as its a cat, and we have turning blocks on each bow. Initially the turning blocks were attached with tape to the bow cleats, once we found it worked we added internal reinforcing, attached padeyes and blocks. We run down the sidedeck, it is a straight run (through slots in the stanchion bases) to the turning block. The snubbers 'start' at the transom. We now terminate, sort of, at clutches, one on each side (we had spares) but we have excess snubber so that we can run through a turning block to a sheet winch. We now have 30m each side. This means our ability to stay within 10% of stretch is much easier to manage, we deploy more chain and more snubber. We started off with 10m snubbers, soon found they were not 'man' enough for over 35 knots, we extended to about 17m, found it was too easy to deploy it all - so have gone to the 30m.

Extending the snubbers is easy, quick trip to bow to release chain lock and then everything can be done from the cockpit and return trip to add the chain lock.

The highest indoor climbing walls here need 30m lengths, so I recycled 2 lead ropes.

Because of how we secure and 'turn' we have no need for dyneema. We are using a common chain hook - i.e. one hook for the 2 snubbers. We use halyard or scaffold knots for the hook (ours is a special hook for a bridle)

You should mark your snubber so that you know how much stretch is occurring.

We have a chain lock, hook on chain secured to a strong point. If one side goes, we have broken 2 snubbers in 17 years, we have the other side and the chain lock.

We are using our 11mm lead rope snubbers with 6mm x G80 chain (replacing 8mm x G30) so we have minimal catenary effect (38' x 7t cat), exclusively alloy anchors, slightly undersized compared to the recommended sized CQR/Delta/Bruce.

Any snubber should be, at shortest, yacht LOA. To look slightly undersized (where has that been said before!) or wimpy is about right - you are looking for stretch rather than strength (remember they are consumables - and free if you recycle). Metal hooks fall off, make a catch to secure the chain. Buy cradle or saddle hooks from the lifting industry - steer clear of the hooks sold in chandlers, they will damage your chain - all the lifting companies say so! Lifting hooks come ungalvanised - paint it, have it galvanised (G70 hooks from the transport industry cost peanuts!). A bridle is better than a single snubber, it will help steady the yacht and halves the work for each snubber.

A main cause of anchors dragging is veering and yawing - steady the yacht, a bridle (and or anchor in a 'V'), cushion the effect of waves, elasticity (and catenary) and you will be much more secure (even at shorter scopes - 5:1 where you might want, but cannot deploy, 7:1. Deepset the anchor (without the snubber - just a chain lock) and you will bury chain, buried chain reduces the impact of any yacht movement on the anchor. Power setting with the snubber - some of the effort of the engine is used to stretch the snubber - silly idea!

There is an article on snubbers in the December '17 issue of Sailing Today.

Jonathan
 
The mixture of nylon (for stretch) and dyneema for chafe protection is more complicated, and perhaps overkill, but is ideal for a snubber. We wilł probably use something similar on the new boat.

The more common approach of a simple nylon snubber is generally perfectly adequate, but in prolonged storm conditions you need to be wary of chafe. Adding a cover over the nylon at chafe points is the usual solution, but the nylon tends to heat up under the cover and this weakens it considerably. Once again, this not a great problem in most conditions, but if you are looking for the ultimate storm snubber a mixture of nylon and dyneema is appealing.

It is amazing how much nylon stretches and on the attached diagram the dyneema length looks a little short. I also dont think the dyneema loop is probably worth the complication. The 12mm nylon section will be wet and get more salt encrustation than the 10mm section. Both of these things weaken nylon, so in practice I think the 12mm section is just as likely to break as the 10mm section on deck, so the dynemma loop adds complication without much benefit.

There are a couple of alternatives that are worth considering. There are some new materials that have good stretch, combined with better chafe and UV protection than nylon. They also don't lose as much strength when wet, or with cyclic loads. Tiptoe is one example. These materials have the potential to make a simple and cheap one piece snubber with many of the advantages of the nylon/ dyneema combination. I think they warrant some experimentation. It is also worth considering Acera to replace the dyneema. It is much cheaper with similar properties, at least for this application.

Finally when talking about the ultimate storm snubbers it is worth considering setting two snubbers in exteme conditions. I have broken quite a few. Replacing the snubber in wild conditions is no fun and there will be a high load on the anchor (and on some boats the anchor winch) until things are sorted.
 
Last edited:
Neeves said:
so have gone to the 30m.
Click to expand...

I think may boats use snubbers that are too short, but too long can also be a problem. Too much elasticity can increase veering which creates more side load on the anchor. I suspect with your policy of always setting two anchors in wind over 30 knots this has not been a much of factor. It may also be that on cat the wide base of the bridle decreases this effect and longer snubbers are better, but for most boats I think 30m of very stretchy 11mm nylon climbing rope would not be the optimum length.

I would at least suggest some experimentation. Don't assume more is necessarily better.
 
Last edited:
Noelex, I have tried it - I would not guess before making a comment. The increased elasticity appears to reduce the veering (with a bridle) and under 1 anchor only. I am not suggesting I 'think' something - I've tried it.

It may only be cat specific - but it has been tried (on a cat, and that has been mentioned)) and its not the basis of idle speculation.

Jonathan
 
Neeves said:
You are trying to keep the stretch of the snubber within 10% of length.
Click to expand...

Where does that figure come from? Seems arbitrary "one size fits all" and maybe a bit low with no mention of differing %MBL/%stretch of different rope construction or manufacturers data.

The rope in question states double that >

Stretch characteristics > 20%
http://www.liros.com/en/products/productfinder/details/detail/liros-handy-elastic.html




 
GHA, actually I think its the stretch that is suggested in the article you quoted from PS, or an associate article.

Nylon stretches between 30% and 40% at break. It does not matter who makes the filament its similar. Nylon the fibre is pretty standard and there is little evidence that new 3 ply or anchor plait has markedly different characteristics. 10% is not arbitrary its about right (in the opinion of people who have tested snubbers and nylon).. More cycles at 20% you have a shorter life. 10% gives you sufficient stretch and longer life.



Are Liros quoting based on a different usage or are they quoting based on usage as a snubber. How many cycles are they quoting for their 20%? I've seen their 20% - I see no need to 'test' their suggestions.

With a 30% to 40% maximum stretch (at which the nylon fails) they seem to be suggesting that 20% stretch (that's to approx 50% of MBS, less than 2:1 safety factor?), repetitively, is acceptable??

But if nylon fails at 30-40% stretch my personal view is that 10% is not arbitrary.

I simply describe our usage - you make of it as you will.

Jonathan
 
noelex said:
It is amazing how much nylon stretches and on the attached diagram the dyneema length looks a little short. I also dont think the dyneema loop is probably worth the complication.
Click to expand...
It is on the edge based on 20& elongation, there's some more D12 stashed in a locker so I'll make a longer one at some point.

Can't agree on being more complicated though, takes a few minutes to splice then it's no different from a single line/sleeve. Possible easier as you don't have to keep the sleeve in place and the nylon isn't rubbing inside the sleeve, it doesn't touch anything so no chance of chafe.

The 12mm nylon section will be wet and get more salt encrustation than the 10mm section. Both of these things weaken nylon, so in practice I think the 12mm section is just as likely to break as the 10mm section on deck, so the dynemma loop adds complication without much benefit.
Click to expand...
Think we're guessing a bit here, the nylon on deck will be salt encrusted and wet as well from waves in a big blow, also no data came up on google so I suspect that's in the "don't know" area. IIRC Evans Starzinger on Hawk used 11mm climbing rope successfully for many years .

Edit - found it :)
http://www.cruisersforum.com/forums/f118/what-size-for-snubber-89713-2.html#post1052006

10mm climbing rope on bigger boat, think I'll try 10mm Liros.
 
Last edited:
As a complete aside, well not quite complete, call it arbitrary.

G30 chain is sold to a 4:1 safety factor, WLL is 25% of MBS

Most shackles, the sort we easily buy, are sold to a 6:1 safety factor, 18% of MBS

Better, higher strength shackles, are sold to a 4.5:1 upto 6:1 safety factor.

Lifting chains are sold to a 4:1 safety factor.

Swivels are seldom tested :( though it does not stop people buying them!

Nylon stretches between 30% to 40% at break - a 10% stretch is a, max, 4:1 safety factor, maybe 3:1.. The 30% - 40% is based on the ideal, no wetting, no encrusted salt, no UV damage, no internal abrasion. 10% is Arbitrary???

10% is based on realistic caution and the need to ensure snubbers do not fail regularly - but they are, or should be considered as, consumables, they do need to be retired (or there be a preparedness to replace at 2am).

Jonathan
 
Neeves said:
Nylon stretches between 30% and 40% at break. It does not matter who makes the filament its similar. Nylon the fibre is pretty standard and there is little evidence that new 3 ply or anchor plait has markedly different characteristics.
Click to expand...

Failure rate against loading actually varies a lot dependant on material construction. .

Graph below show around 1000,000 cycles at about 30% of MBL for nylon subrope and more like 8% for double braid/ 8 strand.

Y axis is log(load range/MBL).

Interesting to note that it's the *range* which will fatigue the rope, so high constant load will be much less damaging than cycling the load.

Not that it helps on a boat where the load will be from zero to lots in a big blow.


https://www.researchgate.net/public...ibre_rope_moorings_for_wave_energy_converters

RrwPEsY.png
 
You must log in or register to reply here.

Share this page

Top