How long a mooring line on the anchor snubber

[TimBennet]

Yep. Will now buy 20m of 16mm 3 strand nylon[\b] when next in a chandlery.

Now I have learned to splice, I will splice the hook onto it

Tudorsailor

How big is your boat? 16mm is really thick. You want the rope to stretch as much as possible so it needs to be loaded to at least half its breaking load.

If the rope in the bridle doesn't stretch, or the bridle isn't long enough for the stretch to be significant, then you might as well just have the chain.

Typically 3 strand nylon will stretch 35% at 75% of it's breaking strain and around 40 - 45% at breakage point.

So 16mm nylon has a breaking strain of over five and half tons, so you would need to be seeing two to three tons of load to be getting the most from your elasticity, which is highly unlikely.

The idea is to make a dynamic, springy, energy absorbing system where there are metres of movement in the bridle. If you secured this system to a midship or aft cleat during storm force or hurricane force winds, you would see a metre or so of backwards and forward motion through your fairleads and no amount of anti chafe would cope with that. So you need to attach it right at the bows where having most of the bridle in the water will help keep it cool and lubricated. Dry nylon gets hot when working! The energy absorbed has to go somewhere.

The rolling hitch is the best form of attachment. Much kinder to the chain and if the bridle does chafe through, you don't loose your shiny hook.

 

[Mistroma]

I use a short length of fairly light 3 strand nylon (8 or 10mm I think) with a chain hook and put out around 3-4m when bad weather is not forecast. That's mainly intended to take load off the windlass, reduce chain noise and avoid dragging chain over the hull if tidal stream pushes the boat forward over the chain.

If weather gets worse then I use a double rolling hitch to attach multiplait and veer around 20m. I think it is 8 or 10mm but can't remember (acquired 50+m in mint condition from a skip).

I always use tubing to avoid chafe and you can usually see the rope moving through the tubing on bow roller even in F4.

I expect to spend more that 100 days at anchor nowadays so think that TimBennet is spot on with his comments.

 

[tudorsailor]

How big is your boat?

I have 49 footer that weighs about 20tons. What size line would you recommend?

TudorSailor

 

[TimBennet]

I have 49 footer that weighs about 20tons. What size line would you recommend?

TudorSailor

Well, on a 7 ton boat I use 9mm, ex climbing rope.
I know Starzinger and Leonard on Hawk use 10mm and that's 47ft and 17 tons, and they reckon 9mm is suitable for a Hallberg Rassey 40.

So, if you can find some 11mm climbing rope (every climber in the country will have some in their shed), I'd start with that.

You are never going to snap it, but it's the chafe both ends that you have to sort out. Even the chain hooks have casting lines in the eye which can wear the rope loop, so you really need to form the loop around a thimble.

Geting the bridle safely through the fairleads and to the cleats is again is a bit of a black art. My solution has always been wrapping about 2 ft of the bridle line in sheets of leather saturated with lanolin.

One typhoon and one hurricane later, it's worked for me!

But these long, thin bridles shouldn't be compared with just trying to stop the chain noise on the roller during the night or banging on the top sides when the tide turns. Six feet of anything will do that.
These elastic bridles are to absorb the peak, shock loadings in gales and worse, when the chain would otherwise be bar tight.

 

[Neeves]

We run our bridles though the base of the stanchions, keeps the rope 'off' the deck - they are no more obtrusive than a furling line. Witchard have a lovely and expensive chain hook with a pin on a spring. The pins are prone to bending but the biggest issue is that you need 2 hands to undo them. Its the same problem with tying the bridle to the chain, it will need 2 hands. You can attach (and detach) chain hooks one handed. We remove our chain hook prior to it coming over the bow roller. Its difficult to believe that having a chain hook is going to cause much wear on your chain, for this to be a real issue you would need to 'hook' to the same links again and again, seems unlikely.

I'd be suspicious of anyone not advising long, like 10m, snubbers - as mentioned anything shorter simply will not have elasticity. Snubbers are sacrificial, you want them sufficiently thin to provide the elasticity (too thick they will not stretch enough). Given that they are thin they will wear. Climbing rope is good because if you go to your nearest climbing wall you will find they retire the ropes, with time, wear or if the rope suffers a severe fall (whichever comes the soonest). They cannot sell them as climbing ropes (or rope for any technical usage) and tend to simply discard them. We picked up 6 x 13/15m FOC.

My earlier post when I mention the light load needed to get 8mm chain off the seabed, it would not take much more load to lift 10mm off the seabed - getting it straight is a different issue. On the seabed and your chain has a frictional 'advantage' which retards veering. Once its off the seabed the yacht is available to accelerate off with any gust and in a 15t yacht the momentum will be large. 10mm chain is obviously better, and 12mm better still, but it would look a bit silly on a 35' yacht. Once the chain is off the seabed, around 20 knots (given that chain size increases with vessel size) is when the snubber starts to earn its passage.

 

[onesea]

Just a thought for all making such a song and dance about this... Personally if anchoring on chain, chain is good enough for me from beginning to end...

Would a snubber be in my vocabulary, only if someone on-board insisted they could not sleep through the noise of the chain reverberating through the boat...

How long would it be? Hmm a few feet long enough to go from my securing point over the bow roller onto the chain...

Do I want a long bouncy cable? Probably not. There seems to be a theory over F6 unless a large size a chain is in use it is all but straight. So there is no benefit from cateinary.

If I was going to pull an anchor out of the sea bed, or shock load a piece of equipment would I do it by:
1) Pulling constantly?
2) Jurking the load up and down creating snatch loads?

What is the easiest way to brake an anchor out?
A) Constant pull one direction?
B) Sheering around on the anchor rode?
C) A vertical angle of approach to the anchor?
D) A Horizontal angle of approach to the anchor?

I figure I want to create a situation of 1 A and D.

This probably leads to the legendary exam board question "The winds is increasing what do you do?" "Put more chain out." "The wind increases more what do you do?" "Put more chain out". "Where are you getting all this chain from?" "The same place you are getting all this wind from".

In the big picture of forces on the anchor is 6" - 24" of stretch going to help? Or is it going to hinder when X amount of boat has 0.5+ knots of weigh on to stop?

When Anchors & cable sizes are measured by weight of boat that surely means they are measured against the dynamic loading of stopping the boat?
If not they would be measured by block coefficient (a basic measure of friction through the water) and Wind-age Areas?

IMHO I do not want the boat sheering round or moving excessively backwards and forwards I do not want shock loads, I want constant one direction pull on my anchor.

In gust conditions with a shifting wind what is the best way to achieve this? Well there are lots of people on here with lots of ideas to think about... Allot depends on the conditions, holding ground and depth of water at the time?



Maybe I should get my coat...

 

[Neeves]

Onesea, Think of the snubber as a bungee. Imagine jumping of a high cliff and your options are: with your ankles tied to a chain or your ankles tied to a bungee cord. Which would you choose? Your yacht has the same choice. The elasticity absorbs the load that otherwise impacts your ankles or on a yacht, impacts the anchor and whatever the chain is attached to. I would be very, very surprised if a windlass is fixed to any yacht with sufficient strength to take that load without support (from a snubber attached to a strong point). Yachts do not enjoy steady loads, it increases and falls continuously (as the chain's catenary acts, the gusts pass through and your yacht swings and sails itself, caused by variation in wind direction). Though the wind direction, on average. might be constant it does vary - considerably (we measured 70 degree variation and it can be more) this leads to swinging about. To minimise the shearing about, yawing (sailing at anchor) will reduce the snatch loading and a bridle, as opposed to a single snubber, will help (but not much unless your yacht is beamy). Another option (comes from the Royal Navy and I think mentioned earlier in the thread), drop a second anchor so that it just drags on the seabed, acts as a sort of friction brake (a bit fiddly if you need to move), someone else, different thread, promoted the use of a V Twin sail on backstay. Another option is dropping a second anchor, maybe so that the 2 anchors are deployed with a 30 degree gap (sort of like a bridle in reverse) - worth it if the wind is forecast as Gale or stronger and consistently from one direction - real nuisance if its going to swing more than about 30 (?) degrees.

Jonathan

 

[onesea]

Neeves,

I understand what your saying but have no plan on pushing my boat of a cliff or moor my boat on an elastic band.

Actually yes the chain might work well if the system was set up right, lets say chain looped over a pulley and "anchored" some distance away. That way the weight of the chain would act gently as the catenary lifted of the ground, or even better sea bed where you would get added damping from the seawater... Obviously the system would have to be designed correctly and set up for the correct weight.... Then I would not get the extra bounce up and down at the end for thrill.

Your analogy is useless like comparing chalk and cheese...

There is a balance to made here... I would expect a well founded cruising boat does have a suitable secure mooring point forward that can take the snatch loads of normal anchoring... The levels effort some people are going to for normal normal night at anchor seem extreme to me...

If you read what I said you will find that I did not say to use one particular technique, so much as point out that the goal of the exercise is to reduce Dynamic Loading and try and create as near to constant force and direction pull on the anchor...

There we agree.

Riding sails is normally the expression used for V twin sails you mention... Over the years people have tried all sorts of ideas how to keep a boat at anchor angels, buckets as sea anchors etc etc... all have there place..

OK Storm conditions it is different, then there is allot more to anchoring in those conditions than and allot of room for debate as to best techniques, sorry you can have all your technology but substantially bigger heavier and longer is normally going to get my vote. More importantly though a suitably sheltered anchorage with good holding and no other boats

At the end of the day anchoring it comes down to shelter and having suitable quantity of good sized gear well attached to the boat, and seabed...

Normal anchoring conditions it is a compromise between handling the equipment, carrying weight and functionality.

IMHO the meter or so stretch supplied by rope even 10m of rope is not going to make much difference in real terms. It does have effect it is worth remembering depending on the conditions it could make the situation better or worse...

 

[NormanS]

I do the same as big ships do,- chain all the way. Use plenty of it, and use a decent size. Most boats' anchor chain is far too light. Many years ago, when I had a 25ft Folkboat, I used 8mm chain, which was adequate, but there are people on here talking about using 8mm chain on 35ft cruisers, and wondering why they drag.

 

[vyv_cox]

I do the same as big ships do,- chain all the way. Use plenty of it, and use a decent size. Most boats' anchor chain is far too light. Many years ago, when I had a 25ft Folkboat, I used 8mm chain, which was adequate, but there are people on here talking about using 8mm chain on 35ft cruisers, and wondering why they drag.

So according to your explanation it's impossible to anchor on rope alone without dragging? Very many boats seem to do it quite successfully, showing your theory up for what it is. The composition of the rode has virtually no effect on anchoring success, it's all in the anchor. Where there is a major effect is in the elasticity of the rode, which is where the thread started.

 

[Neeves]

I do the same as big ships do,- chain all the way. Use plenty of it,

end quote:

comment from Neeves:

In Oz, big ships are ordered from their anchorages and to sit out winds over 25 knots at sea - we have had too many big ships, with all chain (potentially lots of it) and of the right size - up on beaches. Classification Societies, think Lloyds, clearly state that their recommendations, or comments, on anchors and anchoring are restricted to vessels waiting to enter port and are not recommendations for when winds or conditions are adverse. Cruise ships will not anchor over 20 knots - nothing to do with discomfort, they will drag. Nothing to do with chain, they have plenty - their anchors are simply not as efficient as the better (modern) leisure anchors.

end comment

quote

Most boats' anchor chain is far too light. Many years ago, when I had a 25ft Folkboat, I used 8mm chain, which was adequate, but there are people on here talking about using 8mm chain on 35ft cruisers, and wondering why they drag.

I do not recall a single person complaining they dragged as a result of using 8mm chain.

Modern anchors if well set in a decent seabed will not drag. The ride (ie sitting at anchor) might be uncomfortable but a modern anchor should not drag (given the right scope, max 10:1). It might be uncomfortable because of the shock loads - but drag, No! We tested under, rather unusual conditions, and generated 650kg snatch loads - but we did not drag. 650kg snatch loads are like driving into a brick wall. Adding elasticity smooths out and reduces the shock and makes it more comfortable.

Less efficient anchors will drag, but it has little to do with the chain. If you rely on the chain, as opposed to the anchor - I suspect you will drag.

 

[Neeves]

So according to your explanation it's impossible to anchor on rope alone without dragging? Very many boats seem to do it quite successfully, showing your theory up for what it is. The composition of the rode has virtually no effect on anchoring success, it's all in the anchor. Where there is a major effect is in the elasticity of the rode, which is where the thread started.

Sorry,

Our replies crossed, maybe its something to with living in the antipodes.

You commented so much more succinctly, I'm humbled.

+1

Jonathan

 

[vyv_cox]

Sorry,

Our replies crossed, maybe its something to with living in the antipodes.

You commented so much more succinctly, I'm humbled.

+1

Jonathan

Supporting your comment about ships dragging, last year I was giving a talk on anchoring. One of the audience told me that he was ex RN, a deck officer on an aircraft carrier. Above about force 4 they always dragged, at a slow rate, that was continually monitored by one of the crew. Whenever it became necessary they steamed back upwind and re-anchored.

 

[Poignard]

Supporting your comment about ships dragging, last year I was giving a talk on anchoring. One of the audience told me that he was ex RN, a deck officer on an aircraft carrier. Above about force 4 they always dragged, at a slow rate, that was continually monitored by one of the crew. Whenever it became necessary they steamed back upwind and re-anchored.

Maybe they should get a Rocna.

 

[KellysEye]

We used a line where the hook was just above the surface of the water, then we let out a loop of chain again just above the water. A bow cleat is fine, I've never seen a boat at anchor using any other cleat. The line should be slightly stretchy and definitely not polypropolene.

If the chain goes taught then you have too little chain out. You should have enough chain out that it doesn't pull on the anchor, that setup allows for increasing wind strength. Funnily enough that advice has been in the Navy ratings handbook for certainly decades if not centuries, but few seem to know it.

 

[Woodlouse]

In my humble opinion an anchor snubbers only real purpose is to take the load of the anchor chain off the brake on the windlass. The windlass its self should be more than capable of taking any shock loads without parting company with the deck and personally I would be more inclined to attach the snubber to it rather than trust deck cleats.

Any reduction in snatching is of entirely secondary importance. As I said I'd tend to attach the inboard end of the snubber to the windlass and I'd have the outboard end at approximately water level. This should give three to four meters of line on your average 40 footer. I doubt the size of the line is of much consequence as long as it doesn't break. Remember any stretch is going to take the sting out of a shock load.

Personally however I don't use one. But then I've got a heavy boat, with relatively little windage by modern standards and oversized ground tackle. Snatching at anchor has never been a problem. The only time I have used on was when sailing a 100 footer around South America and Patagonia. Then we used a chain hook on 22mm four strand nylon made fast to the bits with the hook just clear of the water. As previously mentioned though, this was to take the load of the windlass break rather than for snubbing snatch loads.

 

[onesea]

So according to your explanation it's impossible to anchor on rope alone without dragging? Very many boats seem to do it quite successfully, showing your theory up for what it is. The composition of the rode has virtually no effect on anchoring success, it's all in the anchor. Where there is a major effect is in the elasticity of the rode, which is where the thread started.

Love the miss quote any anchor system is capable of draggoing...

If you know so much about rode making no difference can you please go and teach this to the boys who anchor oil rigs in the North sea and around the world. The boys on deck would be please not to have to handle 4" chain to moor the buggers it can be a dangerous sport and according to you unnecessary sport...

Yes the anchor is a critical part of the SYSTEM but it is just that a SYSTEM all components add up to make it... Sorry but given a choice I would rather have 30m of chain over 30m of rope... Not saying that you cannot anchor on composite systems just that I would pref-are not to have one...

I do not recall a single person complaining they dragged as a result of using 8mm chain.

Modern anchors if well set in a decent seabed will not drag. The ride (ie sitting at anchor) might be uncomfortable but a modern anchor should not drag (given the right scope, max 10:1).

Can I miss quote you like others on this thread? If I use 8mm chain I will never drag?

ANY Anchor system given enough force WILL drag or breakout at some point. If it will not drag EVER then maybe you could consider a smaller anchor? No need to carry that excess bulk and weight around if it is unnecessary?

Getting the right balance between excess weight and anchor size is a difficult balance... There are NO hard and fast rules, even the best designed anchor system can drag given the wrong circumstances...

 

[vyv_cox]

Love the miss quote any anchor system is capable of draggoing...

???

If you know so much about rode making no difference can you please go and teach this to the boys who anchor oil rigs in the North sea and around the world. The boys on deck would be please not to have to handle 4" chain to moor the buggers it can be a dangerous sport and according to you unnecessary sport...

It is fundamental that the rode must be strong enough to sustain the load on it. All the oil rigs I have been on were heavier than my boat (!!!!!) so of course the chain must be stronger.

Yes the anchor is a critical part of the SYSTEM but it is just that a SYSTEM all components add up to make it... Sorry but given a choice I would rather have 30m of chain over 30m of rope... Not saying that you cannot anchor on composite systems just that I would pref-are not to have one...

It's my choice too, but not because of strength or weight. I like to remain roughly where I am at anchor, not blow all over the water, and I don't like my rode wrapped around others' propellers or my own keel.

Can I miss quote you like others on this thread? If I use 8mm chain I will never drag?

I don't know where you think you read that. What was said was that the weight of the rode has little influence. A decent anchor, well dug in, will hold up to the strength of the rode, whether it is rope, chain, cable or a solid rod.

ANY Anchor system given enough force WILL drag or breakout at some point. If it will not drag EVER then maybe you could consider a smaller anchor? No need to carry that excess bulk and weight around if it is unnecessary?

Getting the right balance between excess weight and anchor size is a difficult balance... There are NO hard and fast rules, even the best designed anchor system can drag given the wrong circumstances...

Of course it will, nobody is saying different. But don't think that the rode composition or weight is contributing to anchor holding because all the theory and a lot of observation says otherwise. In a force 6 and above my 8 mm chain at a scope of more than 10:1 will be completely off the bottom in an almost straight line. How is that contributing to the anchor holding?

 

[onesea]

???


It is fundamental that the rode must be strong enough to sustain the load on it. All the oil rigs I have been on were heavier than my boat (!!!!!) so of course the chain must be stronger.



It's my choice too, but not because of strength or weight. I like to remain roughly where I am at anchor, not blow all over the water, and I don't like my rode wrapped around others' propellers or my own keel.



I don't know where you think you read that. What was said was that the weight of the rode has little influence. A decent anchor, well dug in, will hold up to the strength of the rode, whether it is rope, chain, cable or a solid rod.



Of course it will, nobody is saying different. But don't think that the rode composition or weight is contributing to anchor holding because all the theory and a lot of observation says otherwise. In a force 6 and above my 8 mm chain at a scope of more than 10:1 will be completely off the bottom in an almost straight line. How is that contributing to the anchor holding?

Chain has nothing to do with strength it has to do with weight and catenery and movement through the water. They can make wires as strong as chain (I am sure I am teaching you to suck eggs here) allot of rigs have composite chain and wire some even going chain wire chain wire and other exotic combinations...

Your comments about why you like chain are why I like chain. The same reasons that matter when its blowing a gale and the wind changes, if the boat is not pulling hard she gets a catineary that helps the anchor reset? The friction of the chain in the water helps keep the boat from swinging wildly.

If the chain is pulled all but straight there is no give so the boat will not snatch at the anchor as long as it is holding it will just pull a little harder for each gust... She will not gain a little momentum with the stretch of the nylon, then potentially over compensate when the nylon returns and start snatching?

If the wind shifts the boat will either keep the chain taught or a catinary will appear which then acts like a shock absorber... So yes to me the rode does make a difference, even if it is said to be held off the sea bed in stronger winds...

Ships did not start using chain because it was easy or fun it was because they learned it was better... Modern Anchors have helped but still chain helps too...

 

[Woodlouse]

As far as I know one of the primary reasons for chain is because it is capable of being stored in a very compact manner with very little effort. Rope and wire if simply fed down a spurling pipe will not form anything like the neat heap that chain will.