Dragging of anchors

[thinwater]

Sand is nearly as variable as mud. Coarse, light coral sand and fine mineral sand with a little mud are worlds apart. The later generally sets in a few feet and will break the chain with some anchors (done that).

In the real world:
* Undersized Delta in super soft mud. It was simply overpowered.
* Fortress barely set in hard send/shell. It released with the tide reversed. Fortuantly, I was on-deck, only a few minutes from raising anchor anyway (I didn't trust it).
* Danforth on a wildly yawing catamaran (no bridle, main sail up). This doesn't even count.

During testing (no counting anchors I overpowered, which is nearly all of them)
* Obstruction lifting chain. A stick or limb that guides the chain to the surface.
* Clogged roll bar. Either sticks or weed.
* In-line tandem. The secondary always trips the primary in a shift.
* Hardpan hiding a few inches under the sand.
* Pulsation with waves, particularly at short scope. This can reduce holding 2-3 times in soft mud compared to a quiet anchor. The soil cannot consolidate. I suspect this is a common reason in squalls in crowded anchorages; the anchor was set at short scope with a steady pull. Then the boat starts pitching and bye-bye.

 

[MM5AHO]

I dragged a CQR in Ardinamor (mentioned already above). Similar issues.
Then also same anchor in Pulldobhrain, where amazingly we dragged. We were No 2 in line of four from windward back. We started at No 2, and ended up at No4. I still don't know how we didn't hit the others, Nos 3,4.

 

[NormanS]

I'm not enjoying all this talk of anchors dragging.

I have just (today) left our boat at anchor for four weeks. OK, it's actually two anchors in a Bahamian Moor, each with a scope of about 8 or 9, and they're in good sticky mud, in the Outer Hebrides, so I'm not really worried.

Presumably the "horsing" earlier referred to is the same as the more common term "pitching"? If so, we don't suffer from this, as for any serious anchoring, where the boat may be left unattended for some time, we always choose a situation with little fetch.

 

[thinwater]

Though it varies regionally, the US Navy describes it thus:

Pitching is the up-and-down motion of the bow.
Horsing is fore-aft surging. Some use this to refer to all motion, I think because it sounds nautical.
Yawing and fishtailing refer to right-left sailing.
Sailing at anchor usually means a combination of yawing and surging.

Definitions are tough, because generally they are all mixed together, though pitching tends to be a distinct rocking motion.

 

[Neeves]

And there was me thinking horsing came from hobby horse or horse riding - an up and down movement.

So I've been using it incorrectly - when I've aid horsing I mean pitching (caused by chop) - though pitching might occur together with horsing.

Never too old to learn.

Norman - choosing an anchorage at leisure where horsing, pitching etc cannot occur seems like good seamanship as it removes one mechanism that may cause an anchor to drag. Your yacht being heavy, or heavier, will not have the extremes of yawing that an AWB (or catamaran) might have and you anticipate a change of tension direction by using a Bahamian moor. From previous posts you have made you are well practiced in this art - more so than anyone else has described. I think you have practice on your side.

Jonathan

 

[Neeves]

Maybe few are interested but there are dearth of replies - does this imply people don't drag (Which should be comfort to many - as I said this was not meant to instil fear.

Makes we wonder why everyone, well quite a few, are changing to NG anchors.

Jonathan

 

[JumbleDuck]

Makes we wonder why everyone, well quite a few, are changing to NG anchors.

Judging by the boats I see, most people aren't. It's a no-brainer if you're starting from scratch, but most of us have anchors which work well enough ... as you said, right at the start, a CQR can provide a pretty hefty force, albeit not as much as a <whatever>. I'd be tempted to move to NG in order to use a much lighter anchor for the same (wholly adequate) holding power, but that doesn't seem to happen much.

 

[thinwater]

Judging by the boats I see, most people aren't. It's a no-brainer if you're starting from scratch, but most of us have anchors which work well enough ... as you said, right at the start, a CQR can provide a pretty hefty force, albeit not as much as a <whatever>. I'd be tempted to move to NG in order to use a much lighter anchor for the same (wholly adequate) holding power, but that doesn't seem to happen much.

Isn't that how new tech generally spreads, more through attrition than replacement?

I replaced my Delta because it was too small for very soft mud, and a poor design for that as well (as is any plow). I found it lacking all-around. I would have kept the Delta had it been 2 sizes larger. But I would not buy a new Delta.

I added a NG to a new boat that was only equipped with a Fortress. I kept the Fortress, of course, as it is a superior kedge and soft mud anchor. I wouldn't have bought a plow, but I might have stayed with one if it was large enough.

I doubt an inventive guy like Sir Taylor would be offended that after 85 years his design had become obsolete. He would probably ask "what took you so bloody long?"

 

[Neeves]

Judging by the boats I see, most people aren't. It's a no-brainer if you're starting from scratch, but most of us have anchors which work well enough ... as you said, right at the start, a CQR can provide a pretty hefty force, albeit not as much as a <whatever>. I'd be tempted to move to NG in order to use a much lighter anchor for the same (wholly adequate) holding power, but that doesn't seem to happen much.

The reason for thread was, that as you suggest, holding capacity, or lack thereof, is not the reason anchors drag. Most 'old' anchors have a holding capacity, when tested in a straight line etc etc in ideal conditions, far greater than most people are ever going to experience. So I wondered if hold is not inadequate what facet, or facets, are there that cause an anchor to drag - if there were a pattern, or patterns, underpinning failure it might be useful such that owners could address those issues.

It could be, probably is, a number of factors all interrelated superimposed on which we have vagaries of the seabed and operator error.

I'm of a belief that yawing and pitching are important characteristics - though the replies here do not really support that idea and certainly we dragged, with our cqr clone - for no apparent reason, or not one on which I could hang a hat.

Interestingly - I plotted vessel length v anchor size for average of CQR/Delta/Bruce and Rocna/Supreme/Excel and despite the rhetoric the 2 graphs are almost identical. The manufacturers, if NG anchors have double hold, have simply kept the same weight recommendations but doubled safety factors! Classification Societies allow a reduction weight of 30% for SHHP anchor over HHP anchors - but this has not filtered through to the NG/SHHP anchor makers.

Contradicting all of this everyone says - buy a bigger anchor than that on the manufacturers spread sheet, and this is a common practice. So if you had a 20kg CQR, Rocna might say buy a 20kg Rocna but people buy a 25kg or 30kg model.

Spade and I think Knox appear to have more confidence and suggest slightly smaller anchors vs the Rocna/Supreme/Excel combo

Which would not fit very well with what you suggest should you become unable to resist temptation (and what we did) go smaller. As you will have noticed going smaller does invoke the contempt of some of the experts.


But this was not about size or specific designs as there are no answers (or there might be but no-one will agree - it was simply a means to see if there were any common reasons as to why anchors dragged - and I'm surprised how few people have responded (but maybe its a boring subject and I should get out more!)

Jonathan

 

[jordanbasset]

We were stern to on Port Kalamos a couple of weeks ago (not really relevant but we were moored next to Rod and Lucinda Heikel - nice people) The boat next to them struggled to set their Rocna anchor, finally they lifted the anchor and there was an almost inch perfect rock wedged in it. They got rid of the rock and set as usual.

 

[Neeves]

Equally not relevant

I've mentioned before we once caught a 4.5kg gas cylinder, the toe caught in the handle. It was difficult to remove and very grubby - I was so relieved when I got it off that I immediately dropped it back in the water - and have regretted that decision, and felt guilty, ever since - I should have removed it to somewhere it would not cause so much grief.

 

[thinwater]

The root question, which I have been pondering for years, is whether holding capacity and reliability are always related. We've given examples of fouling that were immediately obvious, but they won't always be. We talk about power setting an anchor, but that only tests it up to about 25-40 knots, depending on the engine and prop (some are weaker in reverse).

In some anchor tests then give full data. Often the anchor that puts up the best number only did well in one set. The others were above the power set force, but just barely. This is common in thin mud. Another anchor did not achieve the same max, but was more consistent. I think I would rather have the latter, but most anchor tests don't share this information, only the the best result. They should also post the worst result that felt like a set, since you have no way of knowing which you actually have. This is a pet peeve of mine.

Short scope (chain well off the bottom--in deep water catenary tends to keep it down--separate discussion) and pitching are an education issue. Same for yawing. The soil science is well known and obvious. I bet the effects are similar on any anchor design that is set shallow. The science says so.

Fouling with junk. A roll bar has contributed a few times, but never cause a trip for me. The Spade has no bar, but the lack of area and angles has made it weak in soft mud. Perhaps someone will figure out how to get ride of the bar without giving up surface area.

Alloy. I don't know enough to comment.

Hard stuff and trash. Are certain shapes (not just sharp, not just low angle) better at cutting through?

---

I kinna pushed this subject with Neeves in a string of e-mails. To me it's not the best set. It's consistency. I think I know how to measure it in sand and mud (report ALL of the pulls, not just the best one). But difficult bottoms are difficult to evaluate.

 

[dje67]

Used to have a Danforth look-alike that I kept as a kedge. Had to use it when my main anchor windlass failed last year, but it was a rubbish old thing with really blunt flukes that wouldn't grip the sand around Cumbrae.... apart from once when I managed, after about 10 attempts, to get it to hold. Later, when I tried to retrieve it, I could barely lift because I'd managed to get the stays of an old, discarded mast tangled around the flukes. It took me about an hour to raise the mast and anchor (no windlass, only halyard winches and ropes). I then couldn't get the mast stays unhooked and was now stuck with an 8 meter jousting pole at the front of the boat....

Eventually cleared it and could then get back into the marina without getting jammed across the entrance...

Anyway, not really a case of anchor dragging, but the opposite I suppose.

 

[thinwater]

Used to have a Danforth look-alike that I kept as a kedge. Had to use it when my main anchor windlass failed last year, but it was a rubbish old thing with really blunt flukes that wouldn't grip the sand around Cumbrae.... apart from once when I managed, after about 10 attempts, to get it to hold. Later, when I tried to retrieve it, I could barely lift because I'd managed to get the stays of an old, discarded mast tangled around the flukes. It took me about an hour to raise the mast and anchor (no windlass, only halyard winches and ropes). I then couldn't get the mast stays unhooked and was now stuck with an 8 meter jousting pole at the front of the boat....

Eventually cleared it and could then get back into the marina without getting jammed across the entrance...

Anyway, not really a case of anchor dragging, but the opposite I suppose.

I've pulled up a shopping cart and a bicycle, in addition to the odd tire, chain, or tree. Fine holding, all of them!

 

[Neeves]

Some anchor tests give an average of a number of pulls, but sometime the worst pull (which might be factorially worse) is discarded. I think this latter is valid if you are making the same decisions with all anchors. A clogged anchor (clogged for whatever reason) is not typical. The Fortress Chesapeake tests provided all of the data for all of the pulls, these were then averaged for each anchor - with discards. All the data for the West Marine tests, published in 2006, is available - with comment on each pull. All of the earlier data produced by Fortress in their tests last century is also available. Anchor Right test data, when they were testing under Robertson supervision, is all available. Ultra data, under ABS supervision is all available.

The Classification Societies when they test for SHHP require that the anchor under test is better than an existing SHHP anchor, so you test one with another. They take an average, allow discards. Thi actually means that as the first anchor tested was a Supreme - subsequent anchors tested are all better and if your comparison is, say Rocna - then the anchors slowly get better (in terms of UHC).

I am not aware that anyone uses the 'best' result in isolation though for validity tests should include at least 3 pulls - the more the better

The main issue with tests are that they are restricted to straight line pulls at a consistent pull rate and this does not reflect reality. In real life pull direction will vary with the veer angle, pull might be snatch loads and the chain might be thrashing as a result of the yacht bow moving up and down.

There is indication, anecdotal, that higher holding capacity does reflect a better ability to resist dragging as NG anchors (with their higher hold) do not enjoy the dragging propensity reputation of the old gen anchors. Interestingly big old gen anchors appear to drag as frequently as small old gen anchors and our experience with alloy suggests alloy NG anchors are as reliable as steel NG anchors - confounding the idea that heavier is, always, better. Additionally I have never heard anyone complain that a Fortress is more prone to dragging than a Danforth. This not suggesting bigger is not better, but there is no evidence except that ridiculously small is, well, ridiculous. Classification Societies allow a 30% reduction in weight of SHHP anchors over recommended weight for HHP anchors for a given yacht - even though to be SHHP the anchor need have twice the UHC. The CS, for no published reason, are hedging their bets - but do credit the better performance (and contradict - bigger is needed)

Apart from catching stones in a fluke most of instances of dragging appear to be caused by rubbish, man made causes. Weed has been mentioned - but given the difficulty of defining weed (or quantifying its characteristics) I'm not aware that any anchor could be considered reliable - best look for the sand patches.

No-one is really suggesting that the action of the yacht at anchor, veering etc, has any impact on anchor stability.

Most people seem to suggest they power set, though this is really only a reliable method of checking an anchor upto about 30 knots (but most people choose anchorages not subject to more than 20 knots, let alone 30 knots).

I measured the tension on a rode in reverse at full revs, well 3,000 revs, on 2 x MD2020 (20hp Volvo) and this corresponds to the tensions on a rode for our cat at about 30 knots. The normal rule of thumb is 10hp per 100kg of tension.

Jonathan

 

[NormanS]

Please tell me how you find these anchorages where the wind will only be up to 20 knots. Only last week, we had Storm "Hector" with winds forecast to be up to violent storm force 11. Yes, we chose a good anchorage for it, but I can tell you that we had a lot more than 20 knots of wind. A LOT more.

 

[thinwater]

My thought is that you discard (with mention) any non-set that would have been obvious. You should never discard a pull that would have been greater than typical power setting for that size anchor. This set would be accepted as valid in the field. In your case, 400 kg tension, but I would argue not all boats have that much power in reverse, so more like 200 kg (441 pounds) for a 35-pound anchor. If the anchor held more than that, it would not be a throw-out in the field. It would have appeared to be well set.

I'm also not sure I agree with simple averaging after throw outs. If one time in five the anchor seemed set at 441 pounds, but in fact would fail at 450 pounds, the fact that it can sometimes hold 3 times that much is nearly irrelevant. One time in five you will drag if the wind comes up, and you will not know which. This is like minimum breaking strength vs. average breaking strength; climbing gear, for example, is rated by the 6 sigma minimum BS, not the average average BS. If we consider anchors to be safety gear, averages and maximums are irrelevant, except as used to calculate a 6 sigma minimum.

In a poor bottom this usually means you can't be sure of anything more than the power set force. In a good bottom, it may come down to how certain you are of the quality of the bottom.

It's a wonder I sleep when anchored... but I do. I'm actually not nearly as paranoid as I come across when playing devil's advocate. I hope you all understand that this is intended to be a fun rhetorical exercise among friends. It's a fascinating topic with much worthy of debate and few certainties.

 

[noelex]

Please tell me how you find these anchorages where the wind will only be up to 20 knots.

+1

 

[Stemar]

Please tell me how you find these anchorages where the wind will only be up to 20 knots. Only last week, we had Storm "Hector" with winds forecast to be up to violent storm force 11. Yes, we chose a good anchorage for it, but I can tell you that we had a lot more than 20 knots of wind. A LOT more.

https://www.metoffice.gov.uk/public/weather/marine/inshore-waters-forecast?

Yes, I know they don't always get it right and local conditions can multiply wind strength, but if a 5 is forecast, you're unlikely to get more than a 7. If a 7 is forecast, I don't know about you, but I'm going to the pub!

 

[NormanS]

https://www.metoffice.gov.uk/public/weather/marine/inshore-waters-forecast?

Yes, I know they don't always get it right and local conditions can multiply wind strength, but if a 5 is forecast, you're unlikely to get more than a 7. If a 7 is forecast, I don't know about you, but I'm going to the pub!

Yes, that's fine, but while you're in the pub, what's happening with the boat? Do you take it in with you?