Dragging of anchors

[Neeves]

I'm a glutton for punishment

Most people have had an anchor drag. I wondered if anyone had thought back on why it dragged?

According to all the holding capacity tests, in good clean sand, an Old Gen anchor of around 15kg will have a UTC of about 1,000kg and a NG a hold of about 2,000kg - far more hold than necessary for the yacht sized to the anchor - as long as the tension is in one direction and that tension is increased steadily (not necessarily valid for most anchoring situations).

Consequently its not hold, per se, that causes the anchor to drag - but some other characteristic(s), chop, yawing, poor seabed (not that ideal sand, beloved of people testing anchors!), clogged fluke, change of wind direction, wrong anchor, short scope etc

Without getting into my anchor is better, or bigger, than yours - what conclusions have people drawn on why their anchor dragged.


Contradicting myself - once when I was testing a whole range of anchors we anchored for lunch using a 5kg Spade and then 5kg Excel - we dragged with either, in soft sand under fairly benign conditions. So size, at the extreme, does matter (we continue to normally use a 15kg anchor (or its equivalent) - which does not drag). We dragged using a CQR with out J24, a combination of not accounting for tide, we had only gone for lunch, but the chop picked up to something quite large and I suspect it, the chop, was the cause rather than the change in depth of water.

Jonathan

 

[Uricanejack]

First off I was always quite happy with a CQR. Usually I find the. "My anchor is better". Threads a bit boring.


The only times I have ever dragged.
I thought the anchor was to small.
Or the scope to short.
I tend to pick regularly used anchorages with reputably good holding so haven't had a problem with holding. Could just be lack of experience.

Personally. I like to use a lot of scope. I like to pick my spot. drop the anchor, go astern lay out a lot of rode. Cleat it off and give it a good pull. If it doesn't hold I pick it up and pick another spot and try again.

Occasionally I sail in down wind. The anchor rode flaked out on deck and cleated off. drop the anchor. Get stopped by the anchor bighting. Stow sails. My wife finds this embarrassing and goes bellow.

I sail quite often with my sister and her husband. They tell me you don't need to do all that its rubbish. We quite enjoy sailing together. On my boat we do things my way. On their boat we do things his way. I don't tell him how to run his boat.

When I sail with them we are always very diligent about picking transits and keeping a good anchor watch. Which is just as well. We quite often get up in the night because we a dragging the anchor.

We have been doing it this way for about 40 years. Quite happily and quite convinced we are both right. He still has a CQR. I have a Bruce.

One complaint I have about the 15kg Bruce. I don't have an anchor winch. Sometimes I find it really hard to break it out when hauling my anchor. Still its never failed to hold.

 

[jordanbasset]

Touch wood I have only had an anchor drag twice when I have set it (always give it 2000 revs to make sure it is dug in). I suspect the reason they did drag on the two occasions was other boats lifting my anchor when they went out. (tied back to the quay stern to)
But have had an anchor fail to set a few times. Invariably due to poor holding, thin layer of sand over rock, thick weed etc

 

[john_morris_uk]

I’m interested where this ‘best holding is sand’ idea comes from. I suspect most people would suggest that the best boxing is thick gloopy mud.

Sand is used in the tests because it’s use is repeatable and the waters clear enough to video or photograph in. Also it might be argued that any old anchor works in mud. Sand is often more challenging.

 

[JumbleDuck]

Without getting into my anchor is better, or bigger, than yours - what conclusions have people drawn on why their anchor dragged.

Not counting the time I stayed longer than I meant and forgot to let out more chain (shades of "We Didn't Mean to Go to Sea"), I have only dragged twice. The first time was in Ardinamir:

There is a fair tide through the places, running NE-SW and there was a fluctuating wind from the SW. Every time the wind rose, we rode to it and the anchor reset. Every time the wind fell we rode to the tide and the anchor reset. The result was a zig-zag track to the north. I had to get up and re-anchor three times during the night, and every time I went on deck to do so at least one other boat there (it was a very popular anchorage in these days) was doing the same. Of course this isn't a true drag, and I suspect that a modern anchor would have had similar issues, though perhaps slightly smaller steps to the zig-zag.

The only other time I've had problems was a couple of years ago ... in Ardinamir again, when precisely the same happened.

 

[KenMcCulloch]

I’m interested where this ‘best holding is sand’ idea comes from. I suspect most people would suggest that the best boxing is thick gloopy mud.

Sand is used in the tests because it’s use is repeatable and the waters clear enough to video or photograph in. Also it might be argued that any old anchor works in mud. Sand is often more challenging.

I agree. My favourite Scottish anchorage in a gale from the west is Isleornsay. Thick clay, even a primitive CQR will just dig in and in.

 

[KellysEye]

I dragged in English Harbour, Union island and Jost van Dyke in the Caribbean all were a thin layer of sand over dead coral I moved around to find sand. You will find the same in some Greek island bays thin sand over rock.

 

[cindersailor]

Dragged in David Balfour's Bay on the Ross of Mull once. Conditions were pretty benign with perhaps 10 kts from the NW, but my 10 Kg Delta certainly dragged in about 4 M with 3:1 scope. I put this down to very soft sand, at least judging by its sinky nature in the shallows on the beach. Have since changed to a 12 Kg Vulcan and recently anchored just along the coast in Traigh Gheal, which seems to have similar sand, without a problem. The beaches along that short stretch of coast are fantastic, pity they all face south.

 

[Stemar]

I had a CQR that held fine, until the day it hooked a trot (the engine died just after I cast off my mooring, strong tide & no wind) and held so well I couldn't get it back. I got a second hand CQR and I could never get the damn thing to set. No idea why. Then a mate hooked a 10kg Delta and a length of chain when retrieving his anchor and, knowing my problem, gave it to me and it's never let me down in over 10 years. (24ft Snapdragon)

 

[Kukri]

I have dragged an anchor twice. The same thing both times - dragged "downhill" into deeper water. Once was on a glacial moraine in a fjord and then history repeated itself as farce at Stone Point in Walton Backwaters when I was trying to be clever and get near the beach on an ultra short scope.

I suspect the problem is most likely to arise when you anchor, in the words of an Admiralty Pilot quoted by HW Tilman, "(Anchorage in this bight must be) prompted by necessity and not by any hope of tranquility!"

 

[RupertW]

I have never dragged once set and always set with hard astern to check the seabed.
When it has failed to set it has been catching on a rock, rubbish or a lot of weed on the bottom and once with a thin layer of sand over large sheet of flat rock.

I probably have a Delta

 

[AntarcticPilot]

I have had an anchor drag twice; both times it came up with a big clump of weed on it. So I think it was dropped on weed and failed to reset on the change of the tide.

Not me, but my Dad's boat - we had a mooring in Dunbar harbour, where the bow was made fast to two massive barge anchors (obtained from a breaker at scrap metal prices) and the stern to the harbour wall. The barge anchors weighed around 2 cwt each (100 kg) each; the nice thing was that the scrap dealer looked at them and said, OK, a hundredweight each - when we came to move them they were clearly WAY more than that! My dad and we two teenagers had to use a complicated system of levers and jacks to get them into a trailer.

The boat was a Halcyon 27, so the mooring was vastly over-specified (the chain, from the same source, would have held the QE2 as well!) The anchors were buried in the harbour floor by the harbourmaster at extreme low water springs. Normally there was not the slightest hint of a problem. However, one weekend there was a massive westerly gale. It was too dangerous to attempt to go ashore in the dinghy, there was a massive swell in the harbour and we later had to watch a friend's boat being smashed up in the harbour. Just when we were congratulating ourselves on riding it out, we felt those two massive anchors dragging! Immediately we started the engine, cut the mooring warps and went through into the inner harbour (we hadn't done it earlier because my dad judged the danger of moving to exceed the danger of staying put - and if the anchors hadn't dragged, he'd have been right.)

No anchor is entirely safe from dragging; if ever there was a setup up you'd have imagined couldn't drag, that was it - and it dragged.

 

[Neeves]

To add to Antarctic Pilot's post - not with an anchor but a 1t lump of concrete.

Our swing mooring in the shelter of Pittwater is, was, simply a 1t block of concrete to which is attached one 50mm chain, 3m I think and then 3m of 15mm chain then a nylon pennant. The block is sitting on sand into which it slowly sinks between services (when it is annually retrieved it usually has sand on the top of the block - so it sinks to about block depth) - it had been serviced about 6 months previously. The nylon is not much longer than depth of water, 10m, and we have short bridle attached at the 'top'. Last year our cat, 7t and 38', dragged the block about 100m (much to the surprise of our mooring service provider). We now have 2 x 1t blocks.


We were part of a line of yachts anchored in Jervis Bay, well south on the Australian east coast. The forecast was for a 15 knot on shore wind. Having had a 15 knot offshore wind all day - everyone stayed put. There was a large fetch. At about midnight the wind was blowing 25 knots and it was getting bumpy and I went out into the cockpit to survey the scene. I watched as yachts one after the other dragged - no-one was yawing - but everyone was horsing. I don't know what scopes people were using - you don't notice these thing with a 15 knot forecast and we were all about the same distance off the beach. I concluded it was the horsing that was the major cause of dragging - everyone but us was using old gen anchors (in clean sand). Discretion being the better part of valour I went to retrieve and was amazed at the snatch loads - the anchor was set as if in concrete.

As an aside - the 2 yachts who dragged just before we bailed out were obviously concentrating on clearing up - and on a dark blustery night it would have been very useful if they had switched their nav lights on - as at this point our radar eventually gave up the ghost.

But I echo Antarctic's comment no anchor is safe from dragging - you might power set but you cannot power set (maximum revs, and how many set at maximum revs?) much beyond the tension developed at 30 knots - so if it blows 40 knots the anchor will set further - and, you might be very unlucky, and may catch something that unseats it.

Jonathan

 

[gus]

Many times sailors will bemoan that their anchor just gathers weed and then blame the weed for their problems. A good sharp point on the anchor is essential so that it has a chance of starting to dig in. If the point is blunt then it has no chance on a firm substrate.

 

[Kukri]

To add to Antarctic Pilot's post - not with an anchor but a 1t lump of concrete.

Our swing mooring in the shelter of Pittwater is, was, simply a 1t block of concrete to which is attached one 50mm chain, 3m I think and then 3m of 15mm chain then a nylon pennant. The block is sitting on sand into which it slowly sinks between services (when it is annually retrieved it usually has sand on the top of the block - so it sinks to about block depth) - it had been serviced about 6 months previously. The nylon is not much longer than depth of water, 10m, and we have short bridle attached at the 'top'. Last year our cat, 7t and 38', dragged the block about 100m (much to the surprise of our mooring service provider). We now have 2 x 1t blocks.


We were part of a line of yachts anchored in Jervis Bay, well south on the Australian east coast. The forecast was for a 15 knot on shore wind. Having had a 15 knot offshore wind all day - everyone stayed put. There was a large fetch. At about midnight the wind was blowing 25 knots and it was getting bumpy and I went out into the cockpit to survey the scene. I watched as yachts one after the other dragged - no-one was yawing - but everyone was horsing. I don't know what scopes people were using - you don't notice these thing with a 15 knot forecast and we were all about the same distance off the beach. I concluded it was the horsing that was the major cause of dragging - everyone but us was using old gen anchors (in clean sand). Discretion being the better part of valour I went to retrieve and was amazed at the snatch loads - the anchor was set as if in concrete.

As an aside - the 2 yachts who dragged just before we bailed out were obviously concentrating on clearing up - and on a dark blustery night it would have been very useful if they had switched their nav lights on - as at this point our radar eventually gave up the ghost.

But I echo Antarctic's comment no anchor is safe from dragging - you might power set but you cannot power set (maximum revs, and how many set at maximum revs?) much beyond the tension developed at 30 knots - so if it blows 40 knots the anchor will set further - and, you might be very unlucky, and may catch something that unseats it.

Jonathan

Keep in mind that the s.g. of reinforced concrete is about 2.4 to 3.4 , give or take a bit for the amount of steel in it, so your one ton block is actually a 583 kg or so to 713kg or so block once it is under water. That's not an awful lot to hold a seven ton 38ft cat. Very many moorings providers use concrete blocks and get away with it because the loads on the mooring in summer are quite low, assuming that the mooring is sheltered and there is minimal "fetch".

I agree that horsing has an awful lot to do with anchors unsticking and moorings parting. People are usually aware of the need to anchor in shelter, with minimal fetch, but often they forget why this is - and it is indeed to reduce the risk of horsing. So when someone anchors close to a tempting shore, perhaps with the wind offshore, others are tempted to join them. Then the wind comes onshore, not necessarily very strongly, with a few miles of fetch... This seems to have been the case in some well known "mass groundings"...

 

[Richard10002]

My sense was that New Gens were all to do with much better ability to "dig in" to the sea bed. My Harbourfast CQR copy seemed to have a tendency to lie on its side and drag along the seabed, unless it got lucky. Whereas New Gens have something built in that encourages/forces the tip to engage with the seabed at the right angle for digging in.

An anchor with a hinged head always struck me as more likely to avoid digging in, than the opposite....

Clearly, whatever anchor you use, it needs to be heavy enough and, if 5kg is not working, but 15kg is, then it's a big clue.... no matter what the holding forces of 1000 and 2000 might tell you

 

[TQA]

I am a full timer living on the hook mostly in the Eastern Caribbean for 15 years. I believe in a 'one size up' anchor all chain rode lots of scope and backing down hard to set the anchor. Generally this give me a good grip on the bottom but I have dragged a few times.

The mysterious ones are when after holding for days in strong gusty winds the anchor drags in light winds for no apparent reason. This has happened in sand and heavy mud.

I relied on CQRs for many years but now have a Rocna.

I am a firm believer in lots of scope and backing down hard, nothing like the bow whipping round to point at the anchor and then dipping.

 

[jdc]

I've dragged almost never in UK waters, and just had the usual suspects of CQR, Bruce and Delta over the years albeit a bit over-sized. (I have failed to set the Delta: funnily enough Isle Ornsay being the worst place where I tried maybe 6 times and it just didn't hold at all (it was blowing a gale). I went further out and it bit at once, so I put it down to a patch being churned up from lots of anchoring over the years and so very soft).

Elsewhere it's always been in very soft mud when I've dragged. The symptoms as experienced have never been exactly a drag, ie a steady and slow inching back, but a sudden let go and the boat just takes off sideways at about 4 knots even with loads of scope (10:1 or more). The Delta is infamous for this amongst Europe yachtsmen visiting S America and so is not popular there. Now I'm back in home waters I'm not rushing to replace it but certainly will if we go back.

 

[biscuit]

I have dragged several times, over a period of years, usually not in extreme conditions. The first time (with a professional skipper, 35ft sailing school boat, CQR ) it was apparent that we had hooked a wooden obstruction.
Once in a friend's boat, through sheer carelessness, the anchor was never set properly. Once on too short a scope in an anchorage which was fine until the increasing wind and swell of a spring tide over topped the protecting reef. Once with a Rocna which happened to have pierced the centre of a discarded wire mesh scallop dredge which was probably buried deep in the mud. (it came up with the anchor) On that occasion, it had held with a good burst of astern, but dragged when the wind increased later, presumably it slowly worked its way out. Unless you are able to dive on your anchor, you can never be 100% sure.

 

[Neeves]

There was no intention that this develop into another anchor scare thread, but

Even if you dive on your anchor you cannot be entirely sure - the toe can till hold something or there can be something buried not far from the toe that will be impaled when the wind picks up. Nothing is certain - but in the real world people have been using Deltas, CQRs and Bruce for decades and they and their yachts are still around.

Furthermore diving on anchor can be more risky that it dragging, crocodile, sharks etc, often the water is too murky (and the anchor has disappeared in soft mud) and for those of us who have reached the age of maturity - the water can be too cold (and it pitch dark). We are 100% sure (and live on that basis) until it drags!

But a piezo electric anchor alarm works very well, though if it ever goes off it might shorten my life significantly!


Minn, I accept what you ay about the SG of concrete - our mooring was specified by the mooring contractor who, with his father, have been providing moorings for many decades (and accepted by our insurers, Pants). He learnt a lesson as well!

I started the thread to try to identify if there were any specific patterns.

When we used a CQR copy we once anchored late afternoon in a long line of yachts down a narrow channel. We had dinner, slept, we were preparing breakfast and the whole line of yachts decided to leave en masse, one after the other.

We of course were dragging, the wind was no different, we had passed through one high tide - and suddenly we inexplicably dragged. Difficult to ascribe a pattern to event like that - and someone mentioned the same earlier.

Jonathan