How long should an anchor snubber be?

[Pelagic]

I agree with Dockhead… you still need a chain stopper to relieve windlass loads.
Length of snubber is really based on the architecture of your belaying points/ bow-bow-spirit clearance/Height/chafe points from dolphin strikers etc.

Personally I like a slack fold of about 3 meters of chain lowered below the water to provide swash resistance when hunting and to keep chain clear of bow perpendicular.

[sabray]

Not all 3 strand is the same. I think if your at 25,000 lbs you are looking for breaking strength of 8,000 lbs so your 9/16 or better. I double up with 1/4 amsteel as a chain stopper. Looped through the chain and back to a cleat. If the snubber fails then that gets one hell of a shock then the windless gets hit. A small belt and suspended approach. I


Sent from my iPhone using Tapatalk

[zboss]

I think you need multiples.

We have been using double 30 foot lengths of 3/8" nylon, one on the port cleat and one of the starboard cleat run out through the hawsepipes with chafe guards, for fair weather. We plan on changing it out every year. So far it has brought us through some horrible nights without incident.

We choose 3/8" because we like to anchor in fair weather but we are acquiring a 5/8" nylon for storm conditions.

[mikeguyver]

Ok I'll bite.
I use my dock lines with the rubber wrap around stretchy snubber devices, works fine. I just shackle a grab hook to the loop and anchor to a cleat and let out a few feet of chain. What's so difficult ? They give about 2' of elasticity before picking up the catenary of the chain and drop off strain smoothly when unloading. I don't have to carry another system just for this purpose and the grab hooks can be used for other purposes when we're not anchored.
Fire away....

[Andrew Troup]

There is a certain degree of 'hall of mirrors' amplification in the www era, whereby a couple or three influential people have seeded some ideas about anchor chain which simply to not stand up to scrutiny, except by lay people (ie the vast majority of sailors).

For example: "A snatch load with a tight chain" is contradiction in terms. For a snatch load to happen, the chain has first to slacken. This *can* happen, either due to a lull, or due to the trough which precedes a wave, but this re-establishes the catenary of a heavy chain, enabling it to effortlessly avert the ensuing snatch load.

Except in the shallowest of anchorages, the only way a snatch load can happen with a tight chain (provided the chain is sized to suit the conditions) is if a heavy object with no inherent resilience were to hit the boat squarely on the bow with the boat already experiencing a very strong wind.

Neither wind nor wave meets this description, at least in relation to a vessel with a 'proper' bow. Possibly if the vessel were shaped like a box, a wave could transfer force to the boat sufficiently suddenly to qualify as "snatch" load, in the situation described.

In the days of light anchors and heavy chain, virtually none of the "Bibles", such as the Glenans sailing manual, Alain Gree's treatise (a full-length book on anchoring cruising vessels), or Robert Danforth Ogg's writings, even mentioned the desirability of elastic snubbers. I don't recall Adlard Coles mentioning the practice.

Hiscock mentions it as a possible enhancement for quietness and increased peace of mind, not as a necessary precaution, and there is certainly no suggestion it was a mainstream tactic.

---------------------------

Using light (all) chain, requiring routine use of an elastic snubber, is a valid method, and has several advantages.

What I object to is that it has been marketed to modern recreational sailors as a "one true belief" proposition

The use of heavy chain, with recourse seldom, if ever, to an elastic snubber is equally a valid method with several advantages.

[sabray]

Cantenary effect gets overcome at some point. Guess you never saw your chain go bar taught.
.What dock line has a thimble. Or are you matching your dock line eye splice to the load? You would be better with a hitch and bag the hook. That's just load dynamics that we know. Heat and chafe are the failure points.. Why I like having dyneema at the chock.


Sent from my iPhone using Tapatalk

[Pelagic]

Break out stresses at anchor are normally associated with the v/l hunting around to maximum shear thus coming up hard on a taught chain that has a wrap on the bow stem.
The bridle effect of a snubber can settle this hunting down considerably along with other techniques.
Testing and adjusting for dynamic conditions on your own boat is the best advice I could give

[Dockhead]

Originally Posted by Andrew Troup

There is a certain degree of 'hall of mirrors' amplification in the www era, whereby a couple or three influential people have seeded some ideas about anchor chain which simply to not stand up to scrutiny, except by lay people (ie the vast majority of sailors).

For example: "A snatch load with a tight chain" is contradiction in terms. For a snatch load to happen, the chain has first to slacken. This *can* happen, either due to a lull, or due to the trough which precedes a wave, but this re-establishes the catenary of a heavy chain, enabling it to effortlessly avert the ensuing snatch load.

Except in the shallowest of anchorages, the only way a snatch load can happen with a tight chain (provided the chain is sized to suit the conditions) is if a heavy object with no inherent resilience were to hit the boat squarely on the bow with the boat already experiencing a very strong wind.

Neither wind nor wave meets this description, at least in relation to a vessel with a 'proper' bow. Possibly if the vessel were shaped like a box, a wave could transfer force to the boat sufficiently suddenly to qualify as "snatch" load, in the situation described.

In the days of light anchors and heavy chain, virtually none of the "Bibles", such as the Glenans sailing manual, Alain Gree's treatise (a full-length book on anchoring cruising vessels), or Robert Danforth Ogg's writings, even mentioned the desirability of elastic snubbers. I don't recall Adlard Coles mentioning the practice.

Hiscock mentions it as a possible enhancement for quietness and increased peace of mind, not as a necessary precaution, and there is certainly no suggestion it was a mainstream tactic.

---------------------------

Using light (all) chain, requiring routine use of an elastic snubber, is a valid method, and has several advantages.

What I object to is that it has been marketed to modern recreational sailors as a "one true belief" proposition

The use of heavy chain, with recourse seldom, if ever, to an elastic snubber is equally a valid method with several advantages.

Snatch loads occur when momentum of the boat is enough to bring the chain tight, taking out the catenary.

I have 100 meters of 12mm chain weighing 330kg. Near the top end of what recreational sailors have in terms of weight of chain. I had a snubber break in a stormy anchorage once and I am here to speak from experience, and not theory, that a snubber can be a matter of life and death even with that much chain. A less robustly built boat (lots of Kevlar and massive scantlings in my boat) would have been ripped to pieces. Nice theory, Andrew, but it works only with weight of chain much greater than recreational sailors are likely to carry, and only in deep anchorages.

[Andrew Troup]

Originally Posted by Dockhead

Snatch loads occur when momentum of the boat is enough to bring the chain tight, taking out the catenary.

I have 100 meters of 12mm chain weighing 330kg. Near the top end of what recreational sailors have in terms of weight of chain. I had a snubber break in a stormy anchorage once and I am here to speak from experience, and not theory, that a snubber can be a matter of life and death even with that much chain. A less robustly built boat (lots of Kevlar and massive scantlings in my boat) would have been ripped to pieces. Nice theory, Andrew, but it works only with weight of chain much greater than recreational sailors are likely to carry, and only in deep anchorages.

It seems eminently plausible that the reason recreational sailors "are not likely to carry" heavy chain is because of recent mythology, in which case it's a circular proposition.

Your chain would once have been considered light for a boat of your size and displacement.

Out of interest: What depth of water were you in? Were you, by any chance, off a beach?

[Dockhead]

Originally Posted by Andrew Troup

It seems eminently plausible that the reason recreational sailors "are not likely to carry" heavy chain is because of recent mythology, in which case it's a circular proposition.

Your chain would once have been considered light for a boat of your size and displacement.

Out of interest: What depth of water were you in? Were you, by any chance, off a beach?

I'm not aware that yachts have ever used super-heavy anchor chains. Working boats maybe. Actually, yachts until relatively recently didn't use chains at all -- rope anchor rode was the norm, until windlasses for yachts started to be mass produced. The problem was windlasses, which started to be mass produced only in a few decades ago. Only recently have powered windlasses been widely available to recreational sailors.

I agree with you in disagreeing with Steve Dashew that the weight of the chain is meaningless (he put 10mm G70 chain in his 65' Sundeer boats for example). I agree with you that the catenary is an important quality in an anchor rode. But I can't imagine a heavier chain than what I have -- it's 1/3 of a tonne of chain, right up in the bows. Anything heavier and you would need a navel pipe and keep the chain in the bilges, which brings with it all kinds of other problems and disadvantages (such as stench in the boat). And I doubt that still heavier chain would bring any significant benefit -- if you need a snubber anyway (and I think you do), then design the snubber to provide elasticity beyond the capability of the chain catenary.

It is true that ships don't use snubbers, but look at the size of their chains. The effect doesn't scale down to our level.

In my really bad chain-snatching case, I was anchored in Studland Bay during a Southerly gale. I especially anchored out rather farther than usual so I was in relatively deep water -- I think it was about 14 or 15 meters. This is a quite deep anchorage by recreational sailor standards. I had all 100 meters of chain out, all 1/3 tonne of it. The wind backed during the night right around to E, putting me on a lee shore and exposing me to the weather and seas. Waves were breaking around me. The really violent snatching came from the bows being caught up in the waves. It was rather terrifying, although I was not very close to the actual shore -- I was several cables off.

But one thing which I observed was that snatching aside -- the wind loads in a moderate gale (F7 - F8) were enough to take all the catenary out of the chain -- the chain was bar tight when the boat was not being tossed by waves. As it was, the chain would slack as the bows fell into the troughs, and would snatch back as the bows were lifted up. It sounded like cannon fire.

I was lucky to get away from that one. I had a crewman motor slowly ahead, and I lifted the chain with the windlass, hanging on for dear life. How I got the 55kg Rocna anchor on board, I have no idea -- can't remember. It was a near-run thing. I think I would not have been able to do it without the Brunton self-pitching prop, which makes motoring slowly ahead possible in such conditions.

Moral of the story: Be more careful not to take a chance of being caught out off a lee beach when anchored, especially in rough weather. And use heavier and longer snubbers in rough weather.

[sailorboy1]

this is what is great about CF, how there is agreement over the complex issues like anchor snubbers

BTW - I have 2 but normally use the 25' 5/8" one as I like the hook on it better

[Rick01541]

Seems to me the catenary effect of the chain will provide far more "stretch" than any length of snubber. I prefer a short snubber so I can easily retrieve it and pay out more rode if the weather conditions warrant it.

[Dockhead]

Originally Posted by Rick01541

Seems to me the catenary effect of the chain will provide far more "stretch" than any length of snubber. I prefer a short snubber so I can easily retrieve it and pay out more rode if the weather conditions warrant it.

The problem with chain catenary as a shock absorber is that it "stretches" less and less, the more force you put on it. It works great at moderate loads, but then at some point the force required to move it another mm goes up steeply, and it stops absorbing energy. When it's bar tight -- and I've seen my heavy chain bar tight a few times -- it doesn't absorb any energy at all.

Nylon rope, on the other hand, keeps absorbing energy right up until its breaking point.

I would recommend a long, heavier snubber for rough conditions. Nylon octoplait is ideal. I have three snubbers on board; my longest is 15 meters and it is 18mm IIRC. A short snubber needs to be thin in order to give enough stretch -- which is fine in light conditions. My short snubber is 12mm line I think. My boat is 25 tons all up; snubbers need to be proportionately lighter for lighter boats.

Nylon loses strength when wet, and will heat up internally and fail if loaded hard and cycled. You should not rely on a well-loaded nylon snubber as the only the thing between you and the rocks -- so always belay the chain in another way (sorry for being a broken record), and a second snubber is never a bad idea, in rough conditions.

I spent nearly a week last summer anchored out in Ushant in a howling gale (out of a clear sky, go figure). The wind almost never dropped below 30 knots and we had gusts of 50. I stayed out of the small boat anchorage and anchored out with the ships in 25 meters of water. I had all 100 meters of chain out, my 15 meter long snubber, and a medium snubber on as a backup. It worked beautifully; we rode comfortably and nothing broke. The Spade anchor didn't budge an inch. I did retire the long snubber afterwards; to do duty as a spring line. And made a new one.

Many sailors never, ever anchor out in rough conditions, so this part of the discussion will be of only theoretical interest. For some of us, however (e.g. those sailing in Australia, New Zealand, English Channel) these things can be a matter of life and death.

[Cotemar]

A good length for and Anchor Snubber is 25+ feet. The longer the better.

Add a rubber snubber for an even smoother ride in a choppy anchorage when the wind and wave kick up.

[Horror Hotel]

Many sailors never, ever anchor out in rough conditions, so this part of the discussion will be of only theoretical interest. For some of us, however (e.g. those sailing in Australia, New Zealand, English Channel) these things can be a matter of life and death.[/QUOTE]


This is exactly why so many have the opinion that catenary is all that's needed. If you don't anchor it terrible weather you don't realize how quick chain goes bar tight. If anchored in a area with tidal area with heavy current, much less wind is required to achieve bar taunt status.