Don't drag your anchor!

[NormanS]

I doubt if the Western Isles will ever be like the Whitsundays. ☺
It is noticeable that although more yachts are visiting the Western Isles, the increasing provision of visitor moorings and pontoons, has meant that the genuine natural anchorages are probably even less visited than before. Suits me. ?

 

[sailaboutvic]

I can't help thinking that, after all these posts, post #5 is still the most applicable.

Richard

I think it's about time we stop talking about 3.1 scope for lists of reasons one is 3.1 is only suitable for windless night and little current or for a lunch time stop , another reason all of us will deferment the depth by our gauge ( 4 mts depth 12 mts scope) but most will forget there another metre is so from the bow to the water ,
I found over the years 5.1 generally is about right taken the depth from the bow ,
The only time I would shorten the scope is if we in a crowded Anchorage and I am happy we in for a quiet night then I anchor at 4.1 other wise I move even if it ment anchoring further out where there less protection .

@jonathan regarding snubbers I can't say honestly that I seen a charter boat with a snubber although an half experience sailor chartering could easily make one up at no cost to him self.
What I found amazing is now and then a skipper would talk about snubbers as if he just invented it ,
I over heard a conversation a few months back , both are supposed to be experience old time sailors like some of us here talking about snubbers , one said his snubber was a metre long just enough to take any strain of the windless and that's all that's needed the other said he had no need of one because he had a chain stopper ,
There no doubt both had any idea what's a snubber was use for so one has to wonder what their anchoring technique was like.
I very rearly get involve in anchoring conversation face to face because just like this forum everyone knows better,
I am happy to help out if needed at time of anchoring if asked or while having a general chat but as soon as I hear guys who are set in their ways talking crap I walk away has I found all that will happen is you end up falling out , believe it or not these normally are the old hands sailors who refuse to accept new ideas ( X has been doing it like this for hundreds of years ) the younger sailors seen to be more open to lean what they are doing wrong .

 

[RichardS]

I think it's about time we stop talking about 3.1 scope for lists of reasons one is 3.1 is only suitable for windless night and little current or for a lunch time stop , another reason all of us will deferment the depth by our gauge ( 4 mts depth 12 mts scope) but most will forget there another metre is so from the bow to the water ,
I found over the years 5.1 generally is about right taken the depth from the bow ,
The only time I would shorten the scope is if we in a crowded Anchorage and I am happy we in for a quiet night then I anchor at 4.1 other wise I move even if it ment anchoring further out where there less protection .

@jonathan regarding snubbers I can't say honestly that I seen a charter boat with a snubber although an half experience sailor chartering could easily make one up at no cost to him self.
What I found amazing is now and then a skipper would talk about snubbers as if he just invented it ,
I over heard a conversation a few months back , both are supposed to be experience old time sailors like some of us here talking about snubbers , one said his snubber was a metre long just enough to take any strain of the windless and that's all that's needed the other said he had no need of one because he had a chain stopper ,
There no doubt both had any idea what's a snubber was use for so one has to wonder what their anchoring technique was like.
I very rearly get involve in anchoring conversation face to face because just like this forum everyone knows better,
I am happy to help out if needed at time of anchoring if asked or while having a general chat but as soon as I hear guys who are set in their ways talking crap I walk away has I found all that will happen is you end up falling out , believe it or not these normally are the old hands sailors who refuse to accept new ideas ( X has been doing it like this for hundreds of years ) the younger sailors seen to be more open to lean what they are doing wrong .

Hi Vic

I agree with you. We always use 5:1 as measured from the bow for overnight stops. If a bay is so crowded that we can't use 5:1 we would normally find somewhere else unless the weather is totally settled but that seems to have become increasingly uncommon as the years have gone by.

We've charted a half-dozen times over the years with both Sunsail and The Moorings and have always been shown how to use the snubber provided by the shore crew before we left the charter base. I understand that some charterers then fail to follow the instructions but I don't see what the charter company can realistically do about that.

Richard

 

[RupertW]

In

Hi Vic

I agree with you. We always use 5:1 as measured from the bow for overnight stops. If a bay is so crowded that we can't use 5:1 we would normally find somewhere else unless the weather is totally settled but that seems to have become increasingly uncommon as the years have gone by.

We've charted a half-dozen times over the years with both Sunsail and The Moorings and have always been shown how to use the snubber provided by the shore crew before we left the charter base. I understand that some charterers then fail to follow the instructions but I don't see what the charter company can realistically do about that.

Richard

I will differ a little here. Although I prefer anything up to 8:1 in a blow I am happy in a crowded anchorage overnight to be at 3:1 provided I’ve done the usual hard reverse once set at slow. I measure from where the chain hits the water so may be fairly similar.

My only issue with short scope is when the wind changes and a boat which was alongside becomes ahead their stern may get very close to our bow if their scope is longer.

 

[GHA]

In

I will differ a little here. Although I prefer anything up to 8:1 in a blow I am happy in a crowded anchorage overnight to be at 3:1 provided I’ve done the usual hard reverse once set at slow. I measure from where the chain hits the water so may be fairly similar.

My only issue with short scope is when the wind changes and a boat which was alongside becomes ahead their stern may get very close to our bow if their scope is longer.

You have to pay........ but interesting piece (2 actually) by one of our own about yawing at anchor in latest practical sailor.
Deep Anchors Stay Put in Moderate Yawing - Practical Sailor
(You'll get twenty six quids worth of usefulness over a year subscribing imho. )

Data shows yawing on a deeply set hook can have a very detrimental effect on holding as well - get that dinghy off the foredeck if the wind is coming

 

[vyv_cox]

In

I will differ a little here. Although I prefer anything up to 8:1 in a blow I am happy in a crowded anchorage overnight to be at 3:1 provided I’ve done the usual hard reverse once set at slow. I measure from where the chain hits the water so may be fairly similar.

My only issue with short scope is when the wind changes and a boat which was alongside becomes ahead their stern may get very close to our bow if their scope is longer.

I agree. As I posted a few weeks ago, we sat out a full gale for several days on the Fortess with 5 metres of chain and Anchorplait. Depth from memory about 5 metres. Only when we recovered the anchor did we realise that due to marking confusion we were at 3:1 scope. The Fortress was deeply buried.

 

[sailaboutvic]

In

I will differ a little here. Although I prefer anything up to 8:1 in a blow I am happy in a crowded anchorage overnight to be at 3:1 provided I’ve done the usual hard reverse once set at slow. I measure from where the chain hits the water so may be fairly similar.

My only issue with short scope is when the wind changes and a boat which was alongside becomes ahead their stern may get very close to our bow if their scope is longer.

I use what ever I have in the locker in a big blow this is why we carry plenty of chain has you Richard and I know In Croatia these blow can happen especially with thunderstorms throughout the summer months ,
My suggestion that we need to stop talking about 3.1 is because lots of newcomers to sailing read these forums and they can easily get them impressions that 3.1 is normal practise

I agree. As I posted a few weeks ago, we sat out a full gale for several days on the Fortess with 5 metres of chain and Anchorplait. Depth from memory about 5 metres. Only when we recovered the anchor did we realise that due to marking confusion we were at 3:1 scope. The Fortress was deeply buried.

This is what I am talking about , someone reading this will think , if vyv can do it so can I , not taken in account you was using a fortress and knowing you that you was most likely to had been anchoring in sand or mud where a fortress would have no problem burning it self , someone else with a less impressive anchor would had a very different experience.
Especially on a different sea bed .

 

[vyv_cox]

This is what I am talking about , someone reading this will think , if vyv can do it so can I , not taken in account you was using a fortress and knowing you that you was most likely to had been anchoring in sand or mud where a fortress would have no problem burning it self , someone else with a less impressive anchor would had a very different experience.
Especially on a different sea bed .

Not something I would do deliberately but does demonstrate firstly that 3:1 scope can work and secondly that the old 3:1 chain, 5:1 rope advice is pretty much worthless.

 

[Neeves]

You have to pay........ but interesting piece (2 actually) by one of our own about yawing at anchor in latest practical sailor.
Deep Anchors Stay Put in Moderate Yawing - Practical Sailor
(You'll get twenty six quids worth of usefulness over a year subscribing imho. )

Data shows yawing on a deeply set hook can have a very detrimental effect on holding as well - get that dinghy off the foredeck if the wind is coming

I assume GHA agrees with the content of the articles to which he linked

The articles seem to suggest that a deeply set anchor with a well buried fluke, shank and some chain resists veering better than a shallow set anchor. This appears to contradict the mantra of buying a big anchor 50kg or (maybe 60kg) instead of the 33kg as the auxiliariary motor of the yacht will set the 33kg anchor more deeply, with more chain and shank buried) than the larger anchor. The article does suggest this is not a panacea (the well set small anchor) but it will help. I might suggest that 2 well set anchors, of the recommended size, set in a 'V' might be batter answer (than the single anchor of the recommended size) or an overly large anchor.

The more recent posts all seem to suggest the idea that a large anchor can be safely used at short scope has few supporters.

Veering is not only caused by some characteristic of the yacht, the dinghy on the foredeck (for example). It can be caused by bullets of wind regularly hitting the anchorage from different directions simply cause be the geography of the surrounding hills. The wind will shear in any event and will then find a different valley through which to pass causing gusts at angles well beyond a difference of 60 degrees. Being anchor with 2 anchors set to counter these extremes might be useful and/or shore lines.

We would very seldom anchor at 3:1, I will not say never, and our common scope would be 5:1 - or more. We would seldom deploy more than 7:1 but if conditions were to suggest a scope beyond 7:1 would be sensible - we would rather deploy a second anchor.

Snubber seems to have been the term for that short piece of rope that was used simply to transfer the tension on the rode to a strong point (not the windlass) and to stop the chain grinding on the bow roller. My vague recollection is that slowly it has been used as the name for a long rope with noticeable elasticity. I cannot recall when the long elastic snubber started to gain popularity - maybe within the last 20 years (?). Bridle has had the same issue - a catamaran bridle is commonly installed to 'manage' veering - any elasticity it has was almost accidental. Its not the old salts that have it wrong - more recently we have stolen their term for another use.

We almost never see long snubbers, in fact its more common not to see a snubber at all. Multihulls invariable have the short beefy bridle installed at commissioning which looks strong enough to lift the cat by crane and must be devoid of elasticity.

Jonathan

 

[noelex]

It is interesting that recommended scopes seem to be gradually increasing.

This is from the famous Hiscock book “Cruising under Sail”:

"Insufficient scope of cable is the most common cause of anchors dragging, and three times the depth of water at high water should be paid out. In depths exceeding 10 fathoms, however, the proportion of chain may be less."

My over 30 year old “The Complete Book of Anchoring and Mooring” by Hinz has the following to say:

“Experience has given us some rule of thumb methods for the propper scope to lay out .....For the working anchor with winds no greater than 30 knots and some protection from the seas, the following values have proven adequate in good holding ground:

All chain 4:1”


Exactly why we are seeing a gradual creep up in the scopes people are recommending is a bit of a mystery. Anchorages are becoming more crowded both with boats and moorings, so shorter scopes are more likely to be necessary than in the days of Hiscock and Hinz. In addition, boats have become larger and are therefore more likely to be found in deeper water and have all chain rode etc.

However, having said the above, in many anchorages there is only the occasional need to contemplate shorter scopes. We have had only two other boats sharing our anchorages for eight months (ignoring a super yacht anchored in very deep water). This is in three countries. Perhaps more boats are staying in marinas? Anyway, over this time we have been able to put out whatever scope we have room for without any fear of inconveniencing others.

It is also important to realise that shorter scopes reduce the holding ability quite drastically. Many anchor manufacturers publish tables showing the percentage of holding versus scope. At 3:1 you can expect the ultimate holding ability to be around 40% of the maximum that would be achieved on a very long scope.

If is is desirable to anchor at short scope, the skipper needs to judge factors such as quality of the substrate, quality and size of the anchoring equipment, the likely maximum wind strength and depth of water to determine if this will be safe (with a suitable reserve). Don’t forget to include the slope of the bottom which can have a drastic effect on the important “effective scope”.

Personally, I am no hero. Currently I am anchored at 6:1 and this is at high tide. Why not? In fact if there more room I would lay out more chain as some bad weather is forecast in the next couple of days and we will still be here.

But with the oversized anchor that I and other cruising boats carry, the predicted 40% of holding capacity at 3:1 equates, at least on paper, to a total holding capacity of a boat equipped with a small anchor but using a much greater scope.

The formula for scope versus holding power and weight versus holding power is well tested and documented, but it is hard to be sure if these formulae are accurate in all circumstances. I think these are better looked at being rules of thumb.

So stay safe everyone. If in doubt, a little more scope is better than not enough, but I hope we do not see a continued increase in the scope people are comfortable with. 4:1 and 3:1 are cerntainly very usable with some commonsense and judgement. It is a shame to rule out these sort of scopes for overnight anchoring as some seem to be doing.

 

[geem]

Lots of talk about anchor weights, scope, extra heavy anchors, etc but one variable that doesn't get talked about so often is sea state. When a 180 degree winds shift hits the anchorage, typically in a squall with heavy rain and all of a sudden your nice sheltered anchorage becomes a very different prospect. The one thing that has made a difference to us when this has happened is a very long snubber. When the bow is going under the waves the dynamics of the boats movement are quite different from being sat in a calm anchorage. The stretch on our snubber can be dramatic. I hate to imagine the loads on an anchor without a snubber in this situation.
We have a 33kg Spade (the correct size for the boat). It hasnt dragged in this situation.

 

[lw395]

I think the reason people used not to talk about snubbers is that all-chain rodes were not so common. Windlasses were not so common. When the weather piped up, people added more rope. It wasn't called a snubber, it was called 'more rope'.
Maybe people's expectations of when and where it's reasonable to anchor have changed too?

 

[NormanS]

One difference that I see that may well be encouraging people to use more than the previously widely accepted 3:1 scope, is that although boats have tended to get bigger, the size of chain has tended to be smaller.
When I had a 25' Folkboat, I used 5/16" (8mm) chain. Now I see 40' cruisers using the same.

 

[dom]

The old 4:1 depth (from bow roller) rule of thumb roughly equates to a 15 degree seabed angle. According to Spade:

“The Royal Navy's test on why anchors drag "if the angle of pull is 10 degrees off the seabed, the anchor's maximum holding power is down to 60%. At 15 degrees, it is further reduced to only 40% of its maximum holding power".”​

Hence Spade recommend a minimum 5:1 scope in decent condition and 7:1 in adverse weather.

These equate to seabed angles with a taught rode of approximately 11 and 8 degrees respectively. Beyond 7:1 the effect of additional scope on seabed angle diminishes sharply.

Seems sensible to me. And we know for sure that the sine tables haven't changed with time

 

[noelex]

One difference that I see that may well be encouraging people to use more than the previously widely accepted 3:1 scope, is that although boats have tended to get bigger, the size of chain has tended to be smaller.

When I had a 25' Folkboat, I used 5/16" (8mm) chain. Now I see 40' cruisers using the same.

Maybe this is a factor. Catenary is effectively lost at high wind speeds, but short scopes are used in more settled conditions where catenary can play a role. Chain sizes, as Norman has indicated, have been decreasing in modern times.

Whatever the reason, maybe this is just an incorrect perception from forum posts, but while anchors have been improving, acceptable or commonly used scopes seem to be if anything increasing.

I don’t have any explanation. It is just an observation.

 

[GHA]

Did everyone just drag more back then?

 

[noelex]

Did everyone just drag more back then?

Yes, good point. I think they did.

Anchoring has become more secure thank goodness . I would put this down to improved anchor designs that work well in a wide range of substrates, as well as increased anchor sizes principally as a result of reliable and powerful anchor windlasses that enable a small crew to comfortably manage higher weights. Greater knowledge has improved techniques such as the more common use of well designed snubbers.

Given these improvements, do we really need more scope than our forefathers?

 

[differentroads]

I'd suggest you need to carry a Fortress, anyway. They seem to come up, in the UK (so I'm told) fairly regularly on eBay, Sarabande pointed one out recently but it was a FX37 (quite big). But I recall other members have bought smaller ones. The Fortress is excellent if you need to kedge off, its good in sand and mud and unbeaten in squishy mud. I would not use it in weed nor stony anchorages. Its also knock down (though I recommend it is carried assembled so ready to use). It is relatively flat (you can store it tied to the transom) Of the other anchors and it will be your primary, I would suggest Spade as it is knockdown and you mentioned that as a criteria for choice. I would not touch a Mantus, for the reasons outlined in the link in post No 9. If you value hold in an anchor then to buy a Mantus of the same hold as a 10kg Spade or Rocna you will need a 20kg Mantus. If you want the hold of a 10kg Delta - you will need a 10kg Mantus. Spade also does not carry Morgan's Cloud negativity for clogging. If you want to keep weight down in the bow then the aluminium Spade is an option. If you know people going to and from OZ I can recommend the aluminium Excel, we have used one for years as replacement for our steel Excel. In small sizes aluminium anchors will fit into checked in luggage. You could also try Anchor Right and see how much it would cost to airfreight one to you.

If you do need to retrieve by hand then aluminium anchors are so much easier than the steel versions. Our Spade and Excel both weigh in at around 8kg and are the same size as the steel versions each weighing 15kg. The extra weight is noticeable but more noticeable if you have to carry them down the side deck. 15kg is not that heavy - but becomes so on a moving deck when you need to squeeze round shrouds etc of deploy from a dinghy.

Jonathan

Excellent advice except I have to add a cautionary note re Spades and clogging. Last year my Spade dragged twice (in 47 anchorages) and both times it came up with a big ball of clay even after power setting and appearing to hold firm. One one of those occasions I swam over the anchor and noticed it had left a longer trail than normal before appearing to set and I could see what looked like thin sandy over a plate of rock. No anchor is going to do too well in that!
My second anchor is going to be a Fortress to replace the heavy lump of Danforth that I have now. Ideal as a kedge or a stern anchor, which I've recently started using a lot to keep my bow into the waves. And a very good spare bower anchor to boot.

 

[Neeves]

But with the oversized anchor that I and other cruising boats carry, the predicted 40% of holding capacity at 3:1 equates, at least on paper, to a total holding capacity of a boat equipped with a small anchor but using a much greater scope.

The hold of an anchor is determined by the yacht and the conditions under which the anchor is set (engine power or wind) NOT by the size of an anchor. For a Delta its ultimate hold is around 1,000kg in a reasonable sand seabed and the the yacht for which this 15kg anchor would be suitable has at best a 30hp engine and can develop a tension of 300kg (roughly). If the tension developed by wind was 500kg the conditions on the yacht would be such to result in divorce.

The article in Practical Sailor, linked by GHA above, clearly underline that veering is possibly a major cause of dragging (and I and the author) think hobby horsing, due to chop, is another cause. However an absence of holding capacity is not the culprit - UNLESS hold is a function of an ability to resist veering and horsing.

If you have the recommended sized anchor you can set it deeply and shear strength of the seabed increases with square of depth. If you have large anchor you simply cannot set it deeply - it will have the same hold but it will not be set deeply and has less ability to resist veering. As the article in PS says - deep set an anchor and you can rely on the shank, a vertical fluke, to resist sideways forces - veering. A smaller anchor will bury more chain - and chain resists veering. The transmission of movement down the chain, the yacht horsing, veering any vibration from the rigging or boom are not transmitted so effectively through buried chain (and a good snubber). If you anticipate a veering wind - set 2 smaller anchors deeply - much more reliable than one big anchor.. A moving anchor, veering, horsing, vibration down the chain will reduce the shear strength of the seabed in immediate proximity to the fluke and negatively impact hold. Manage that movement - and you improve the opportunity for your anchor to hold.

The PS article shows that a shallow set anchor loses more hold as a result of veering.

Interestingly when large commercial anchors are deployed the focus is on deep set and the chain becomes part of the hold calculation.

If you want to maximise depth of set then power set to the maximum of engine revs, and hold at that maximum for upto 30 seconds - as the anchor sets deeply its ability to dive further slows - give it a chance. Get rid of the swivel - it is an impediment to diving (burial). If you really need a swivel think of a bent link - if made correctly they are smaller area than the chain and add more of that vertical fluke to resist veering. Next time you are thinking of a new anchor chain - think of a smaller HT chain (as the oil industry does). If you don't use a snubber longer than a few metres, change now and introduce a deck length , as a minimum, snubber NOW. Everyone carries a second anchor - capable of replacing the primary (people do lose their anchors) if your yacht is subject to veering or the anchorage is subject to bullets separted by more than 45 degrees - think of setting a second anchor - if the winds are to be over 30 knots. Veering is a killer for any anchor. If you use a grossly oversized anchor your second anchor needs to be grossly oversized as well, the second one is there in case you lose the first so the same rules for choice apply - its now your primary. Carrying 2 grossly oversized anchors seems ridiculous when 2 anchors of the recommended size would suffice. If you control veering, take windage off the bow or deploy 2 anchors - the anchorage will be more comfortable. A veering yacht is debilatating and no single anchor will alter that. Obviously if you are real man (and have no crew) this will not worry you.

Reading back through the thread comment has been made that their, usually Delta, did not work in thin mud - carry a Fortress and use the anchors best suited to the seabed.

There is no quantitative data to support use of oversized anchors, in the same way there is no quantitative data to support use of large anchors at short scope. It is 15 years since Rocna was introduced and despite the hype (and maybe because there is no data to support the mantra) the vessel size vs anchor size spreadsheet has not changed.

There is data to support use of better anchors.

It merits underlining - Noelex anchor is 50kg or 60kg and has the hold of a 25kg or 30kg Rocna (or a 50 or 60kg Delta). Rocna would suggest a 33kg for a yacht of his size, 50'. I can well imagine why Noelex has such a large anchor - why he did not choose a smaller one of a different design is very much a mystery. He mentions, only recently, he chose his anchor because it sets well in a hard substrate - its a big sacrifice for an illusory or rare seabed - to illustrate Vyv has mentioned in all his decades sailing his anchor was only defeated once due to a hard seabed. We have never been defeated by a hard seabed.

Jonathan

A further thought

So, all serious long term cruisers and livaeboards carry oversized anchors - I'd like to see the data (but do not expect it to be forthcoming). I wonder if the 'big anchor' reasoning is similar to the reasoning of the popularity of the necessity to drive a 4x4, particularly in Knightsbridge To me - the arguments are specious.

 

[Neeves]

Some years ago I established a thread to identify whether those who used modern anchors had ever dragged and if so what were the reasons for the drag.

Dragging of anchors

The response basically was - modern anchors do not drag - as no-one admitted to dragging. I'm not entirely convinced, that modern anchors never drag (as Morgans Cloud have a different view) and the absence of 'bad luck' seems unlikely. But taking the results as being honest then whatever scope people were using a few years ago was perfectly adequate (and I would assume is little different to today) and suggestions that 'we' are using less safe scope is erroneous. Scope may have changed - but there is no indication that whatever those changes are have resulted in an increase in insecurity.

Differentroads, post 98, is suggesting a different scenario (bad luck) nothing to do with scope.

Its worth mentioning - the scope, and the ratio of depth (+ height to bow roller) to chain deployed and the angle developed by that ratio and catenary has very little to do with the angle of the tension on your anchor. When a modern anchor sets it buries chain and the angle is determined by the anchor the shackle develops as it is buried - whatever your scope - the angle of the shackle is inevitably higher. Some anchors, Mantus, Fortress do not bury chain until they have fully 'disappeared) if they bury completely at all (photographs seldom show fully buried Mantus - scope then remains important. For a Rocna, Excel or Spade its the shackle angle that determines the tension angle - and modern anchors appear to be very accomodating of high(ish) tension angles - when deep set.

There is no one rule fits all situations in anchoring. It is dangerous to try to categorise all anchors, all rodes etc as behaving the same. Unless posts contain enough detail one person's experience may not be valid to others.

Jonathan