Dragging of anchors

[sailaboutvic]

Its actually about 14m long, one on each side (its a cat). 11mm lead climbing rope (lead rope has the greater (or greatest) elasticity). They join, scaffold knot. at a common shackle that holds the chain hook. I'm not into knots so do not know if this is the best - but it has worked - and fits a 3/8" bow shackle with the hook using the pin.

10m would be about right on most 40' ish yachts and is manageable.

Why do you ask?

Jonathan

Just comparing it with what we use,
our is 9 mts long on each side, made of of 3 ply 10mm stretchable nylon on an eye grabhook,

I notice a lot of people have very short subbers, hanging off their bow.
Not doing much Good.

 

[Robin]

Vyv,

But you'll need a bigger yacht if you want to sail to windward - Catch 22?

He jests

Jonathan

Catch 22s went upwind very well in their day ( IOR quarter tonners IIRC). in my early years I had a Trident 24 triple keep version that went much better upwind afterI put a lead ingot up in the bows so weight up front is not always harmful. We later had 180 ft of 10mm chain on our Sun Legende 41 and nobody passed us in that going upwind!

 

[Robin]

+1. That's my take on it too, but I'm sure that there's a certain amount of following of fashion, and showing off. Why else would someone have a shiny, mirror finish, stainless anchor, (of any design)?

I changed ours, 33lb claw, inherited with the boat even with 15ft of S?S chain so as not to stain foredeck, changed back (?) to a 45lb galvanized Delta. If you fancy a S/S claw I have one for sale, collection only mind!

 

[charles_reed]

To answer Jonathan's original question - in 158 anchorings I've had two drags with the current new-age anchor. 1. Was a complete sea-grass rhizome about 2m long.
2. a drowned branch. Both after setting for 30" @ 2800r pm in reverse.
Overall, the great benefits are the speed of setting and lack of "creep" in high winds, compared to the CQR.

 

[vyv_cox]

Nice report!

But - I think you are saying that in gusts, 24 knots, all the chain is off the bottom - all 32 metres. I'd expect that without a snubber, but would have thought with the snubber you might have some chain on the bottom.

Can you describe your snubber and, for the sake of those sitting at home in armchairs - what happens if you take the snubber off (to the chain on the seabed).

Jonathan

My snubber is 11 mm nylon braid on braid with a forged chain hook. My normal practice is to let enough out so that the hook is below the surface, probably about 3 metres. This time, in deference to the rather stronger winds, i let out a little more, so maybe 4 metres. I then make sure that sufficient chain is let out to form a decent loop alongside the nylon. Have not tried with chain only.

The chain I am using is 8 mm, typical for a 35 ft boat. If I had a boat of a size that required 10 mm chain presumably its windage would be such that the effect on the chain would be very similar.

Some years ago I anchored in a very windy spot just south of Bonifacio Strait. We saw almost 40 knots of wind on occasion. We were in a remarkable bay where the sandy bottom comes up very slowly, so anchored in 2 metres with about half a metre under the keel. In the end I had 30 metres of chain out, a scope of well over 10:1. That was the first time I witnessed all of the chain lifting off the bottom.

 

[Robin]

The posts so far have tended to concentrate on the setting and holding ability, or otherwise, of anchors. But looking at my final comment, above - do members have comment on the ability of their anchor, modern or otherwise, to cope with changes in load, primarily wind, direction. Many will be able to say, I hope, that their anchor copes well with a gradual wind change, the anchor does whatever it does (shuffles round) and they do not really notice, except the yacht swings through x degrees (but the anchor stays effectively in the same place). The worst case scenario is a sudden wind shift, thunderstorm passing overhead, sitting to tide and a big front passes through - and then the anchor is initially loaded in one direction and then loaded at say 180 degrees. If you are anchored in a river the tide will impose a 180 degree load direction change - but the loads, unless the wind is with the new tide is not going to be that strong. Any experience(s).

Some tests I did seemed to show many anchors would shuffle round, modern or pre modern, with a load direction change upto about 150 degrees but beyond 150 degrees they would sommersault and need to reset. If an anchor re-sets of its own ability and particularly in questionable seabeds - then surely that is a positive attribute and merits highlighting.

Jonathan

Over very many years I learned to avoid strong wind over strong tide conditions because the resulting maypole dancing antics in a busy anchorage would be a real PITA. We never dragged doing that but the chain would get under the bow and scrape the paint or the gelcoat. We were lucky perhaps to be able to select anchorages where we would lay consistently to the wind and any cross tidal flow did no more than make a slight change to the angle of pull. If we expected any serious change in wind strength or direction then we would move anchorage to one more suitable, that to me is simple commonsense defensive anchoring. We would sometimes wake up to find no wind much and with our anchor in plain view just as it was when set, with the boat laying to the chain weight alone. we used one anchorage that was subject to a 180 deg wind change at nights when a boisterous sea breeze offshore on an island beach during the day would become a nasty onshore wind off the mainland 12 miles away at night. If we expected this to happen ( it was never in a 'forecast') then we either switched to another beach the other side of a headland around sunset or we set the anchor for the expected wind and made sure we had no boats potentially upwind of where we might sit when the wind came. If the wind didn't shift we would still be in place with the anchor usually still in it's original place having had no shuffles, no breakouts no hassle.

We always use a snubber line because in my book snatch loads are very effective at breaking out anchors. Ours used to be about 20ft of around 12mm diameter 3 strand nylon, with a rubber dog bone mooring compensator wound into it, the line attached to the chain via a cast S/S chain hook. our latest boat hs a less convenient foredeck and bow roller layout and so we now use a 3 strand nylon bridle, still attached via a cast S/S chain hook but now each arm of the bridle has a rubber dogbone mooring compensator wound into it we do not see strong tide flows much these days (unless we were to anchor in the Gulf Stream) and so wind direction and depths are our main considerations. We have always and still do seek out a place clear of obvious weed and detritus on which to drop the anchor and we power lower the anchor to our chosen spot before then gradually laying out the required chain ( we have all chain for anywhere we are likely to go these days) and gently but firmly setting the anchor under engine. If we sail in, then we would dig the anchor in under engine once the sails were stowed after backing the main to get some initial 'reverse' under sail.

I'm not sure if my literary skills adequately convey our routines which evolved over many boats of many sizes from 20ft to 47 feet with all sorts of anchors and over many years in multiple locations but starting from the days when even visitor moorings were rare let alone marinas. Even when marinas appeared we still preferred to anchor, being parsimonious, and the last time that I remember we went walkabout was from a visitor mooring that broke at the riser chain, after which we anchored regardless on our own known and well trusted tackle. BTW I was the (unpaid)' Mooring Master at one YC for several years and as such responsible for laying club moorings in quite an exposed harbour location. We used heavy, retired, chain ferry chains as ground chain and home made Danforth style anchors, weighing around 120lbs or more a piece with 2 such used for each single boat mooring and with 1 inch stud link ferry chains in between. Now those would be fun to carry and set from a small boat! . , We could of course had we known have used a 10lb Rocna on all rope and saved ourselves a lot of effort. .

 

[Delfin]

My snubber is 11 mm nylon braid on braid with a forged chain hook. My normal practice is to let enough out so that the hook is below the surface, probably about 3 metres. This time, in deference to the rather stronger winds, i let out a little more, so maybe 4 metres. I then make sure that sufficient chain is let out to form a decent loop alongside the nylon. Have not tried with chain only.

The chain I am using is 8 mm, typical for a 35 ft boat. If I had a boat of a size that required 10 mm chain presumably its windage would be such that the effect on the chain would be very similar.

Some years ago I anchored in a very windy spot just south of Bonifacio Strait. We saw almost 40 knots of wind on occasion. We were in a remarkable bay where the sandy bottom comes up very slowly, so anchored in 2 metres with about half a metre under the keel. In the end I had 30 metres of chain out, a scope of well over 10:1. That was the first time I witnessed all of the chain lifting off the bottom.

For what it is worth.....

Our snubber is 30' of 3/4" octoplait for stretch attached to the chain with a Plasma soft shackle. The octoplait is coupled to 1/2 dyneema for chafe resistance over the roller and incorporates an Ultra rubber snubber that lets me gauge the forces involved by observing the stretch. As I recall and I suspect you can correct me, the force imparted to the vessel goes down by the square of the distance over which the force is applied. So a good snubber setup changes the force of a taut chain from transmitting the full load to a fraction of that load as the snubber stretches and creates a longer distance over which that force must be distributed.

 

[vyv_cox]

As I recall and I suspect you can correct me, the force imparted to the vessel goes down by the square of the distance over which the force is applied.

Sorry that's new to me and I'm not sure I understand it. Any references?

 

[sailaboutvic]

Sorry that's new to me and I'm not sure I understand it. Any references?

Once you worked it out please let me know,
I was never that good at maths

 

[Delfin]

Sorry that's new to me and I'm not sure I understand it. Any references?

I checked and it isn't the square, it is just distance. The formula comes from Maritime Safety and is F = D (in tons)*100 *V2/d. It is shown as "a general formula", but in essence demonstrates that if the snatch load of a rode is dissipated over a distance, that distance is the critical factor in determining the peak load. If a snub line dissipates the force over 5 feet, the instantaneous peak force is 1/5th what it would be if the distance is 1 foot. I think Alan Fraysee uses the same formula in his calculations of anchoring forces.

Bottom line, if a gust of wind occurs when the chain is tight and imparts 1,000 pounds of force, then a snub line attached to the chain that stretches 3 feet in that gust will reduce that load to 333#. Could still be wrong on the math, but I think this is correct.

 

[Delfin]

I've been looking for Alan Fraysee's Excel spread sheet I once had that gives a whole lot of information on anchor loading, but can't find it on my system. Bummer, as it was excellent. I wonder if anyone else has a copy?

 

[geem]

I checked and it isn't the square, it is just distance. The formula comes from Maritime Safety and is F = D (in tons)*100 *V2/d. It is shown as "a general formula", but in essence demonstrates that if the snatch load of a rode is dissipated over a distance, that distance is the critical factor in determining the peak load. If a snub line dissipates the force over 5 feet, the instantaneous peak force is 1/5th what it would be if the distance is 1 foot. I think Alan Fraysee uses the same formula in his calculations of anchoring forces.

Bottom line, if a gust of wind occurs when the chain is tight and imparts 1,000 pounds of force, then a snub line attached to the chain that stretches 3 feet in that gust will reduce that load to 333#. Could still be wrong on the math, but I think this is correct.

On our 19 ton ketch we use a 16mm three strand snubber on a chain hook with 10mm chain. When the wind gets to 40kts in gusts we would typically have 10ft of snubber over the bow and I would take the snubber to the middle clear instead of one of the bow cleats. This gives a useful extra snubber length but keeps the snubber chain hook off the bottom in the lulls. This set up makes a dramatic difference to the surge felt on our yacht when wind shifts and gusts hit us. Down below in these conditions you hardly notice the gusts. Only looking at the wind instrument in the nav station do you realise what is happening outside. Without the long snubber it is very noticeable.
I have read somewhere in the past that under storm conditions a snubber of approximately boat length is needed to reduce snatch load. This would seem about right to me from my experience.

 

[Delfin]

On our 19 ton ketch we use a 16mm three strand snubber on a chain hook with 10mm chain. When the wind gets to 40kts in gusts we would typically have 10ft of snubber over the bow and I would take the snubber to the middle clear instead of one of the bow cleats. This gives a useful extra snubber length but keeps the snubber chain hook off the bottom in the lulls. This set up makes a dramatic difference to the surge felt on our yacht when wind shifts and gusts hit us. Down below in these conditions you hardly notice the gusts. Only looking at the wind instrument in the nav station do you realise what is happening outside. Without the long snubber it is very noticeable.
I have read somewhere in the past that under storm conditions a snubber of approximately boat length is needed to reduce snatch load. This would seem about right to me from my experience.

You might try a soft shackle to attach the snubber to the chain, as it won't come off like a hook can and is stronger.

 

[Ravi]

I notice a lot of people have very short subbers, hanging off their bow.
Not doing much Good.

Yes, but although not that significant, even this slight stretch will reduce the amount of shock force on the cleat / windlass.

[edit start] I have since seen Delfin's post which seems to give some mathematical credibility to my theory. [edit end]

 

[Ravi]

Returning to the original theme of experiences with NG anchors.....

I had a hazy bar conversation a while ago with a chap who told me about an interesting NG encounter he had witnessed. After a typical Med crossed anchor encounter ?in Lakka?, which involved lots of motoring and tugging in the harbour, some bloke resorted to his dink to sort out a snagged anchor. He found that his Rocna-type had snagged another anchor - literally. The other anchor had somehow managed to get forced through the round hoop at the end of his anchor. Allegedly, after many minutes of trying to extract the captive anchor, it still would not budge. They took the anchors onto the quay and it was only after about 20 minutes of effort and much unnecessary advice from a gathering crowd that they managed to separate the two.

So, apparently, it is not just rocks that Rocnas can pick up.

 

[Neeves]

This is repetitious but again.

Our super long snubbers, around 14m, are attached at the horn cleats on the transom and run up, through the reinforcing slots of the stanchion bases, to the bow, We now have dedicated turning blocks on the bow, previously we had blocks attached to the bow cleats. The snubbers then meet, forward on a common shackle with chain hook. We effectively only have about 4.5m (each side) forward of the bow, and as the cat is over 6m wide we have little forward at all, so the snubber cannot drag on the seabed. We use a chain hook because trying to thread a soft shackle through 8mm chain is not easy. You could use the same system on a mono hull with only one snubber - you simply need to devise a way of getting the snubber 'off' the sidedeck and over the bow - an obvious way is through the bow fairlead but you might need to account for abrasion (Delfin uses Dyneema) but you could simply use hosepipe. We use climbing tope because it is the most elastic cordage available that is also sufficiently strong. Unfortunately climbing rope because of the method of construction (to increase elasticity) defies splicing and I note that someone (Evan Starzinger) who had a similar system to ours has returned to conventional nylon so that they can splice a dyneema tail to reduce abrasion. We have a potential abrasion point where the climbing rope might foul the kicker wires for the prodder (bobstay and bowsprit?) and we have sheathed the rope with hollow Dyneema tape (Nautilus Braids in NZ) - you could use hollow nylon tape - available from good mountaineering shops, (Joe Brown et al). Our snubbers are permanently deployed, as they run between the stanchions they are unobtrusive. We had thought of installing a padeye in the transom, instead of the horn cleat, but have not got round to it.

Mantus have a chain hook with a gate, that seems to work well - except that the chain hooks are enormous, a bit agricultural. Witchard also have a hook with a lock, we find it a bit fiddly - needs 2 hands - and the spring pin is said to be prone to bending and locking open or shut. If you look at the Mantus lock you could make one yourself for whatever hook you currently use. I made one, took - maybe 15 minutes.

All our experiences with our, small, anchors are with long snubbers. As much of the load is taken by our snubbers - its all about energy and the nylon absorbs the energy - then our 'success' with small anchors might not be replicated if you had no snubber.

Short snubbers, as mentioned are simply not so effective - but do take the load off the windlass. Most I see - and I see very few snubbers in use at all, are maybe 2m in length. 2m snubbers effectively have minimal elasticity and you should assume you effectively have none.

These dogbone rubber snubber things - they are equivalent to about 2m of nylon, they are expensive for what they are, heavy and they have a low a finite load limit. Find the Practical Sailor article on snubbers and there are tests on these rubber dogbone devices. Nylon will 'work', basically, upto its load limit - of say 2t for 10 or 12mm (more for thicker), rubber snubbers will snap long before that The advantage of nylon is that it will work over the complete range of load you throw at it, its elasticity is almost linear. Obviously the higher you load it, to its limit, you will reduce its life. The more times you use nylon, as a snubber, you will reduce its life. Anchor plait, or multiplait is no better.worse, than 3 strand but multiplait is easier to store.

Snubbers are consumable, we have had two break with age/wear and carry 2 spares. We have a long enough tail on our snubbers to deploy maybe another 3 or 4 meters if its really breezy. if your nylon is too thick it will not stretch as much, if it is too thin it will stretch a lot, but have a shorter life. 10/12mm is about right for a 35'/45' yacht on the basis of a 10m deployment. In 50 knots! (at the masthead) you might need to deploy more snubber or have a second, storm snubber.

Modern anchors when subject to very strong winds can set extremely deeply and can be difficult to break out (especially a Fortress). I'm of the opinion that more anchors (shackles and swivels) are damaged during anchor retrieval than in use 'as an anchor'. The loads, as Delfin is suggesting (all the maths is in Practical Sailor) when using an appropriate snubber are factorially reduced - but this does not happen when you retrieve - in fact as the scope shortens as you reduce the chain length deployed, the loads can factorially increase made worse as you have no elasticity in the system and the only way to breakout a deep set anchor is to load it with the chain and let boat movement 'ease' the anchor out. Despite advise - sometime we do not have a choice of anchorage or Mobo goes past unexpectedly causing waves over which we have no control.

Jonathan

 

[Robin]

Jonathan,

When we used a single snubber line with rubber dog bone, we actually carried two such lines, the second one had a heavier duty rubber dog bone that need a much higher load to stretch it out to the limit of the nylon coil windings wrapped around it. We reserved this for our 'storm snubber' but in reality it very rarely got used as we would not choose to anchor in storms if we had good advance forecast information and if we did so would be even more cautious about our chosen anchorage that it was well protected from the anticipated wind and wind changes as well as being protected from swell direction. I we had one rubber dog bone fail but in a mooring line in our home berth not in a snubber, it had been in use for over 5 years and may have been weakened by exposure. to UV. I cannot recall ever choosing to anchor with a 'this will stand anything the gods can throw at us attitude', I like to think out options and plan for events not be overtaken by them even if the gear to do so is on board because deploying it in extremis would be difficult for a short ( ie two) handed crew.

Nowadays the bridle with two rubber dog bones that we now use is occasioned by having our foredeck cleats on the teak toe rail right on the deck edge and not having a second, unused, bow roller. With a dog bone in each arm of the nylon bridle I guess the snatch loads are shared between them and each will take it's turn to absorb a swinging yaw snatch as the directions of swing reverse.

Nothing 'anchoring is ever simple black and white to make a definite, conclusive statement! .

 

[Neeves]

Jonathan,

Nothing 'anchoring is ever simple black and white to make a definite, conclusive statement! .

Spot on! Additionally 'our' anchoring conditions are completely different to 'yours', scope, chain, anchor etc might be the same but seabed, wind sheer etc will all be different and only very subjectively recorded (or described).

The dog bone rubber snubber devices should be installed based on the suppliers/manufacturers instructions and these usually require a specific number of turns of cord round the snubber. The number of turns limits the amount of stretch of the rubber snubber - and if you stick to the specified number of turns you do not overstress the rubber and it should have a reasonable life (no idea what reasonable might be). If your snubbers are subject to a greater load than the turns allow then any additional load/stress/energy is taken up the the nylon (because the turns stop the rubber taking any more stress). Consequently when the chips are down - you rely on the elasticity of the nylon - the rubber only provides support at lower wind speeds.

We all try to anchor in as sheltered a spot as possible, we (for example) will move miles if something nasty is coming, we have time and the safer anchorage is within safe striking distance. But on these threads there is the fairly regular report of unforecast, often short, sharp, swift, storms or specific and local wind events of 50 knots - and at times like that you (or your anchor) need all the help you (or it) can get (becuase you get no warning and you cannot move). What we need are devices that work at 40-50 knots not 20-30 knots - of whatever - and nylon will work through the whole spectrum.

I'm not knocking rubber (much!) every little helps.

What we find, for a catamaran bridle, is that the load is on one side then the other, they might be shared momentarily as the yacht yaws through the centre. The arms do not share the load but the load frequency is halved - I guess that theoretically a bridle should last twice as long as a single snubber. But a bridle reduces yawing (so the intensity of any loads ought be reduced) and if you are using 2 anchors in a 'V'/fork there is an even further reduction in yawing. Ideally this could be measured but I only have one load cell and you really need to record load on each arm at the same time.

Jonathan

 

[Delfin]

Spot on! Additionally 'our' anchoring conditions are completely different to 'yours', scope, chain, anchor etc might be the same but seabed, wind sheer etc will all be different and only very subjectively recorded (or described).

The dog bone rubber snubber devices should be installed based on the suppliers/manufacturers instructions and these usually require a specific number of turns of cord round the snubber. The number of turns limits the amount of stretch of the rubber snubber - and if you stick to the specified number of turns you do not overstress the rubber and it should have a reasonable life (no idea what reasonable might be). If your snubbers are subject to a greater load than the turns allow then any additional load/stress/energy is taken up the the nylon (because the turns stop the rubber taking any more stress). Consequently when the chips are down - you rely on the elasticity of the nylon - the rubber only provides support at lower wind speeds.

We all try to anchor in as sheltered a spot as possible, we (for example) will move miles if something nasty is coming, we have time and the safer anchorage is within safe striking distance. But on these threads there is the fairly regular report of unforecast, often short, sharp, swift, storms or specific and local wind events of 50 knots - and at times like that you (or your anchor) need all the help you (or it) can get (becuase you get no warning and you cannot move). What we need are devices that work at 40-50 knots not 20-30 knots - of whatever - and nylon will work through the whole spectrum.

I'm not knocking rubber (much!) every little helps.

What we find, for a catamaran bridle, is that the load is on one side then the other, they might be shared momentarily as the yacht yaws through the centre. The arms do not share the load but the load frequency is halved - I guess that theoretically a bridle should last twice as long as a single snubber. But a bridle reduces yawing (so the intensity of any loads ought be reduced) and if you are using 2 anchors in a 'V'/fork there is an even further reduction in yawing. Ideally this could be measured but I only have one load cell and you really need to record load on each arm at the same time.

Jonathan

Personally, I don't use the dog bone rubber thingie for stretch, but as a poor man's load cell. If it is blowing like stink, its stretch is an easy way to visually see the loads involved.

 

[geem]

You might try a soft shackle to attach the snubber to the chain, as it won't come off like a hook can and is stronger.

We don't have a problem with the chain hook coming off as it doesn't touch the bottom. The chain hook is very strong and convenient to deploy and remove. I forgot to mention that the snubber line goes through blocks on its way to the bow roller and the line is protected from chafe as it goes over the roller with hose. All very easy to use and works well as it is. It has taken some time to perfect it