The great anchor debate - whats are take

[roly_voya]

There have been a nuber of pretty active threads since YM published the article on anchor is the december edition but I wanted to start a debate here because the way livaboard/long distance cruising boats use anchors is different. For one thing who else is going to anchor in january!!

If you havent read the article its worth a look but I can't say I was particularly impressed. It got me thinking though and so did some of the stuff on the treads so I have done a bit of digging.

First thing was that many people who sell anchors give very scant information although notable some of the 'new' manufacturers and a few chandles are better than most (congatulations to rocna and marinestore).

The second thing was that what was recommended was very different from what was recomended in Ian Nicolsons' Boat Data Book which I have used extensively in refitting the boat. Anchor sellers suggested 25-35lbs for main bower for general use whearas Nicolson recommends 50lbs for coasal or 2x 70lbs for long range!! (this is for a 32ft 6.5T sloop)

This was a starting piont, but in order to understand weather an anchor system was good enough I needed to know not just what pull it would hold but what pull the boat would put on it. The most valuable thing in the YM artical was the address for Alain Frayssee site which is at www.tinyurl.com/5goox and is outstanding, anyone going long distance or frequently anchoring should definatly read this.

Working from this data I worked out that for my boat In need the the anchor to resist the following (for 32ft 6.5 ton sloop) using 'traditional' anchors:
Up to F6 about 600kg, pretty much anything will do and 25lb with short chain and rope road would be fine
Up to F8 about 1400kg, the max recommended anchors at 35lbs is going to struggle unless the holding is exellent I need to go up to 45lb to be comfortable
For a true storm anchor capable of standing up to F10 the load goes up to 2582 and even the 45lb is not enough I need to go to tandom 45lb which are then good up to cat 1 hurricaine (5000kg at 70kn) at which piont the 10mm chain breaks!!! (This data is based on reserch published by the American ABYC but in fact assumes less conservative figures than they give as the ABYC covers any boat including cats which have much higer draf factors than my boat)

So my conclusion is that Nicholson is right in recommending at least 70lb anchors for long range cruising and what most people are advertising (eg 35lb CQR) for my boat is only correct for up to about F7, presumably you are supposed to get into the local marina if the forcast is worse than than - not helpful if you happen to be in the north of Scotland at the time.

The other recomendation is that I should be setting abot 5:1 scope of 10mm chain with a 15mx20mm link of good strechy rope as a 'shock cord' to stop snubbing - for 20m depth thats 100m chain weighing 225kg plus about 90lb (40kg) anchors, total 265kg or more than 1/4 ton and thats just bowers! I any case I would always opt for an all chain main rode because of the risk of rope chaffing but its a good job the boat is a good load carrier

If fact I can confim this works because the winter before last I left the boat on exatly tackle that while visiting me mum for christmass in Fishgaurd (there are no mooring you have to swing on the hook) and it blew force 10 for 2 days. I was fine but the 100ft seagoing tug moored next to me sank.

So am I tempted as the artical suggests to sell the CQR's. Well I have never had a problem with dragging and not on grounds of wt because most of the wt is in the rode and you still need that. But if the new style anchors realy do hold 5000lbs+ (which the tests do seem to show) then I would only need 1 and could set a second on the spare rode to allow for wind shift etc or if I lost an anchor. With my current setup I am only really equiped for up to F8 using a single 45Lb and keeping the other as the spare or layed out as a second anchor for wind shifts etc. If I tandom them I loose the backup and I cirtainly don't want to carry a a spare pair!!

What does anyone else think?
Whats you experience of anchoring in storm force winds and how did it work out?

 

[robind]

Isn`t the general opinion that one should place enough sea room between your boat and the sticky out hard bits, in such weather that it won`t matter. Anyway most insurance companies won`t pay out if the boat is unnoccupied at anchor during such times? If you are talking about leaving a boat in a Hurricane hole at anchor you are more likely to attract damage from other boats, so someone on board would be the way to go even to just start the engine to reduce the pull on the anchors! As for size use the biggest and best possible and the correct scope. as for type it depends on the bottom. I would always have available a " Fishermans" for rock or weed and keep your existing anchors as they seem to be adequate for the purpose! Amidst all this calculation and cogitation don`t forget chaffe and shackle weaknesses and ways to lessen the jerk on the rode ie and Angel and (whats the other thing called where you use a chain hook or rolling hitch and a suitable springy bit of warp )

 

[beneteau_305_553]

I have put your data into the synthesis calculation and for a 10 m boat in a F10 (59 kts) in 20 m of water the estimated tension is 1050 dN (1000 kg approx).

A 15 kg CQR would be sufficient and 30 m of 10 mm chain and 100 m of nylon rode would also be sufficient if the holding is good (as normally found in a recognised anchorage)

I havent seen where the damping effect of the weight of the anchor chain is calculated but the surge loads due to wave action and yawing can as stated have a factor of 2.2 (or 5 if on a short chain) at the boat end.

An anchor line with nylon rode with chain at both ends sems to be the ideal provided you have enough space.

The web site is excellent.

 

[KellysEye]

I've always been slightly sceptical about anchor tests - seems to me it's impossible to replicate conditions of (say) a backing F7 with a swell coming in without actually doing it.

Having done it in real life, FWIW we (38 feet, 15.2 tons) carry a 45lb CQR and 300 feet of chain as a main anchor. Plus another 200 feet of chain and hundreds of feet of rope for a 60lb CQR and a big Fortress - for use in strong winds. Also we use 7 x depth. I think it's the combination of anchors and chain/rope that matters rather than looking at a single anchor. Basic rule is don't let the chain lift off the ground, it's worked for us but I could be wrong.

 

[charles_reed]

Re: The great anchor debate - the critical missing factor

Lots of blether and half-baked opinion masquerading as proof, in the ongoing anchoring debate.

What all seem to miss is the most important point, the bottom, or holding, is far more significant than the type or weight of anchor used.

I anchor overnight about 60-70 times a year and drag about 5 times a season.

Invariably dragging occurs after a blow, when wave action is interrupting the catenary effect of the chain, and it occurs when the bottom is hard sand or shingle.

This is in a 3.5 tonne boat on a 12kg CQR. I've tried heavier anchors the improvement is offset by the inguinal repairs required.

Scope much above boat length + x2 the depth of water merely increases the likelihood of a drag.

 

[KellysEye]

Re: The great anchor debate - the critical missing factor

[ QUOTE ]
the most important point, the bottom, or holding, is far more significant than the type or weight of anchor used.

[/ QUOTE ]

Absolutely right, we've dragged only once when we tried to anchor on what we thought was sand but turned out to be a thin layer of sand over a smooth coral shelf i.e. no anchor would have held. But assuming the bottom is suitable for anchoring...

[ QUOTE ]
I anchor overnight about 60-70 times a year and drag about 5 times a season...Scope much above boat length + x2 the depth of water merely increases the likelihood of a drag.

[/ QUOTE ]
I really can't see that scope calculation, it's not logical and maybe it's why you drag so often? Put another way, try letting out half a mile of chain and see if it makes you drag more (bearing in mind the top point) - of course you won't, albeit we find 300 feet is quite enough.

 

[roly_voya]

Hi Hunter

"I have put your data into the synthesis calculation and for a 10 m boat in a F10 (59 kts) in 20 m of water the estimated tension is 1050 dN (1000 kg approx). "

Interesting, the figure I get is 1416dn but that assumes a steady wind of 59kn which neve occures. The calculation I show assume lulls of of 33kn and gust of 78 with a mean of 52. The difference is significant as surge created may be the thing that breaks the anchor out and start dragging.

Yes I do realise this is all very theoretical but hey, Its Nov, the weathers dire and the boats in dry dock what else have I to do? Hopefully a bit of theoretical investigation will back up the practical experience else why would anyone bother with RYA theory courses.

 

[craigsmith]

[ QUOTE ]
There have been a nuber of pretty active threads since YM published the article on anchor is the december edition but I wanted to start a debate here because the way livaboard/long distance cruising boats use anchors is different. For one thing who else is going to anchor in january!!

[/ QUOTE ]One of the other things long distance cruisers have to contend with is varying bottom types, more so than you find around the UK. Accordingly, it would pay to look for advice from those who have the experience, and largely discount that from those local pot-holers who have very specific limited knowledge.

[ QUOTE ]
The second thing was that what was recommended was very different from what was recomended in Ian Nicolsons' Boat Data Book which I have used extensively in refitting the boat. Anchor sellers suggested 25-35lbs for main bower for general use whearas Nicolson recommends 50lbs for coasal or 2x 70lbs for long range!! (this is for a 32ft 6.5T sloop)

[/ QUOTE ]Two things here.

1) Anchor sellers are motivated to suggest lower sizes, as it makes their product appear better ("you can get away with a smaller one") and cheaper. The fine print on quite a few brands is very interesting. "Sizes are working anchors and should not be used in winds above 20 knots". Etc.

2) What dictates holding power is simply resistance, which you get from fluke area. Accordingly, anchor size should not really be chosen based purely on weight.

We recommend a 15Kg / 33lb Rocna for your boat. While at the upper end of your bracket of "anchor sellers", that is still substantially less than Nicolson. I would suggest not that Nicolson's advice is bad, but that it is based on his experience with older anchors such as the CQR, and their relatively small fluke sizes. We in fact consider our recommendations to be very conservative - our calculations are based on 60 knots wind.

There is a problem with most of the existing bibles in that they are a bit out of date with respect to anchoring. More than half the anchors in the SAIL and Yachting Monthly testing are less than 10 years old.

[ QUOTE ]
This was a starting piont, but in order to understand weather an anchor system was good enough I needed to know not just what pull it would hold but what pull the boat would put on it. The most valuable thing in the YM artical was the address for Alain Frayssee site which is at www.tinyurl.com/5goox and is outstanding, anyone going long distance or frequently anchoring should definatly read this.

[/ QUOTE ]Yes it's good, but also severely flawed. While its conclusions are generally sensible, some of the math and models used are far too primitive and do not go far enough in their analysis.

[ QUOTE ]
The other recomendation is that I should be setting abot 5:1 scope of 10mm chain with a 15mx20mm link of good strechy rope as a 'shock cord' to stop snubbing - for 20m depth thats 100m chain weighing 225kg plus about 90lb (40kg) anchors, total 265kg or more than 1/4 ton and thats just bowers! I any case I would always opt for an all chain main rode because of the risk of rope chaffing but its a good job the boat is a good load carrier

[/ QUOTE ]There is no "right" scope; more is better, and the minimum depends on lots of factors. 5:1 is not really adequate in shallow water for really bad weather. In 20m depth you could probably get away with less, and you certainly would not need 100% chain.

Fraysee's recommendations for a snubber are valid, but they are a little over-blown (the stress on the chain will never approach infinity, for example), and they don't consider several disadvantages including the sailing effect that can be exacerbated from too much stretchy stuff. Over a series of cycles of surges (you will notice Fraysee only considers one complete cycle) this can build into a severe problem. You don't want a bungee cord.

These arguments are also affected by scale, i.e. boat size.

[ QUOTE ]
But if the new style anchors realy do hold 5000lbs+ (which the tests do seem to show) then I would only need 1 and could set a second on the spare rode to allow for wind shift etc or if I lost an anchor. With my current setup I am only really equiped for up to F8 using a single 45Lb and keeping the other as the spare or layed out as a second anchor for wind shifts etc. If I tandom them I loose the backup and I cirtainly don't want to carry a a spare pair!!

[/ QUOTE ]Tandem anchoring isn't to be advised for normal circumstances. If your primary anchor isn't adequate on its own in 99% of all deployments, you need to upgrade. However, it is one way of dealing with extreme conditions. It seems unnecessary to carry two pairs, although considering how serious you are, it is not unreasonable to carry four anchors total. Remember however that tandems should always be the same type.

I would suggest you do as you seem to be leaning, get some newer anchors, at least one decently sized one that you can rely upon, and have the others to serve changing roles as back-ups, spares, auxillaries, and tandems.

[ QUOTE ]
Lots of blether and half-baked opinion masquerading as proof, in the ongoing anchoring debate.

[/ QUOTE ]Certainly...

[ QUOTE ]
What all seem to miss is the most important point, the bottom, or holding, is far more significant than the type or weight of anchor used.

[/ QUOTE ]That's like saying the most important factor keeping an airplane in the air is the, ummn, air.

Since it is a constant and one that can't always be changed, it is only sensible to look at what else may be improved.

[ QUOTE ]
I anchor overnight about 60-70 times a year and drag about 5 times a season.

[/ QUOTE ]Well that's close to a 10% failure rate. Do you think that's good?

[ QUOTE ]
Scope much above boat length + x2 the depth of water merely increases the likelihood of a drag.

[/ QUOTE ]I hope that was a mistake - either way it is completely incorrect. The more scope the better, as touched on above. Secondly, there are many factors involved in determining adequate scope, but boat length is irrelevent.

 

[charles_reed]

as I tried to point out

my experience is that extensive scope results in greater likelihood of dragging, not less.

As this is contrary to percieved wisdom I don't expect ready acceptance.

 

[charles_reed]

<<That's like saying the most important factor keeping an airplane in the air is the, ummn, air.

Since it is a constant and one that can't always be changed, it is only sensible to look at what else may be improved.>>


Well yes it is as any competent pilot will tell you.

In hot weather or at high altitude you have far less lift, decreased load and increased take-off.

Try anchoring on thin sand on coral and you'll find your Rocna anchor pretty useless, in fact any "large fluke area" anchor is disadvantaged, however you might get some purchase with a Bruce or Fisherman.

<< Quote:
I anchor overnight about 60-70 times a year and drag about 5 times a season.

Well that's close to a 10% failure rate. Do you think that's good?>>

Well my anchoring is mainly in the Med, only occasionally do I have the nice sticky mud and shallow water one enjoys around the coast of the British Isles. Lots on rock over sand, lots of deep water. So I think it's reasonable - and I've never dragged in a blow.

 

[kalessin]

[ QUOTE ]
We recommend a 15Kg / 33lb Rocna for your boat.

[/ QUOTE ]

Just out of interest, how would we obtain a Rocna anchor either in the UK (where we are) or in Portugal (where the boat is), other than by wiring a large amount of money to New Zealand?

[ QUOTE ]
There is no "right" scope; more is better, and the minimum depends on lots of factors.


[/ QUOTE ]

Surely more scope is not better in a busy tidal anchorage? If everyone else is on 3:1 and we're on say 6:1, we're very likely to swing on to somebody when the tide turns.

 

[kalessin]

Using two anchors

[ QUOTE ]
There have been a number of pretty active threads since YM published the article on anchor is the december edition but I wanted to start a debate here because the way livaboard/long distance cruising boats use anchors is different.

[/ QUOTE ]

Good idea to post here, and can I ask the question which I also asked on another forum: how many of you actually set two anchors - either in tandem or in a "V", on separate rodes - and how often? I'm not so interested in the technical aspect, more in real-life experience!

 

[jimbaerselman]

Re: The great anchor debate - the critical missing factor

Charles,

If you drag 5/60 times, there's something wrong.

Do you always test the set of the anchor by motoring astern? Or if mooring stern/bows to, by attempting to pull the anchor home with the winch?

Your winch should stall before the anchor moves, and the anchor should be able to hold you against full astern on a moderately powered sailboat (not snatching).

Your comment about scope I don't understand. Quite simply, the rode should never arrive at the anchor shaft at an angle greater than 10 degrees off the bottom (give or take an inch). In the conditions I've just quoted, which emulate shock loads caused by yawing around the hook, that implies a 6 times your depth at the waterline.

Unless you're anchoring on a slope!

 

[craigsmith]

[ QUOTE ]
Just out of interest, how would we obtain a Rocna anchor either in the UK (where we are) or in Portugal (where the boat is), other than by wiring a large amount of money to New Zealand?

[/ QUOTE ]By waiting for our British distributor to get set-up (first shipment on its way by sea now). If you are in a hurry but don't want to use a wire, you can talk to us about other forms of payment.

[ QUOTE ]
Surely more scope is not better in a busy tidal anchorage? If everyone else is on 3:1 and we're on say 6:1, we're very likely to swing on to somebody when the tide turns.

[/ QUOTE ]Purely in the context of performance, other factors notwithstanding.

 

[davidbains]

Craig, are you displaying your anchors at the LBS?

 

[KellysEye]

One thing that hasn't been mentioned is riding sails. We use one whenever the wind goes over about twenty knots and it definitely cuts down sheering, taking strain off the anchor chain. Just a thought.

 

[jimbaerselman]

If three times the depth meets the 'setting test' in my previous post, fine. You've proved the point that some bottoms are quite exceptionally sticky.

Otherwise, if you're in less than 10m, I'd lay 6 x (or whatever passed the holding test), and wait for those with less scope to cruise past me - if the wind got up.

Referring to the use of two anchors - you'll remember my post in the other forum. Yes, I use two anchors in three situations: To reliably survive a tide turn; to minimise yawing snatches in strong winds; and to reduce scope when swinging room is very limited.

I'm aware that I'm very much in the minority. But my early sailing years were spent in Brittany on a sailing trawler with novice crews, a very unreliable engine, and a skipper who'd learnt his skills under sail alone.

 

[charles_reed]

Re: The great anchor debate - the critical missing factor

<<If you drag 5/60 times, there's something wrong>>

Possibly, perhaps my criterion is a bit high, >40m from anchoring point constitutes a drag and includes all drops - anchor will probably re-set, but that's not good enough if it's crowded. The usual reason for a drag is bottom detritus, plastic bags, old nets/traps, weed.
There is of course too good a hold, as when the anchor fouled an unmarked, sunken pontoon in the Guadiana and I had to dive to recover it in 8m of liquidised mud.

<<Do you always test the set of the anchor by motoring astern? Or if mooring stern/bows to, by attempting to pull the anchor home with the winch?Your winch should stall before the anchor moves, and the anchor should be able to hold you against full astern on a moderately powered sailboat (not snatching)
>>

Yes, that's when lack of hold usually occurs, but no way will the anchor ever hold at full revs in reverse, the screw is a Brunton 3-blader driven by a 3YM20. The winch is manual so I don't have that option, of tripping the cut-out.


<<Your comment about scope I don't understand. Quite simply, the rode should never arrive at the anchor shaft at an angle greater than 10 degrees off the bottom (give or take an inch). In the conditions I've just quoted, which emulate shock loads caused by yawing around the hook, that implies a 6 times your depth at the waterline.>>

The boat is very wind-rode and sails freely up to and round her anchor unless it's blowing >F4. A long scope allows her to pick up sufficient speed to yank the anchor up.
What I try to do is find a mud bottom, choose the deepest point and drop the hook in there. The problem is that mud bottoms are few and far between in the Central Med, though the Adriatic is better. Drags occurs on thin sand on rock or pebbly bottoms or when the anchor gets something on its point.
Besides when you're single-handed recovering a long scope is very undesirable.

<<Unless you're anchoring on a slope!>>

Nice flat bottoms, like mud are few and far between, so by definition one is frequantly anchoring on a slope. If it isn't it's usually rock.

 

[KellysEye]

Re: Using two anchors

[ QUOTE ]
how many of you actually set two anchors - either in tandem or in a "V", on separate rodes - and how often? I'm not so interested in the technical aspect, more in real-life experience!

[/ QUOTE ]

Yes we have set anchors in a V shape on about half a dozen occasions in strong winds - worked very well, but it's a hardly measurable percentage of how many times we've anchored. If we were expecting the wind to go round the clock we would use a Y configuration.

Never tried anchors in tandem, I'm a bit uneasy about the idea and whether you could be certain even one of them was set i.e. motoring full astern against two big anchors and lots of chain may not do it - or maybe it will, I just don't want to take the risk.

 

[craigsmith]

Re: The great anchor debate - the critical missing factor

[ QUOTE ]
Try anchoring on thin sand on coral and you'll find your Rocna anchor pretty useless, in fact any "large fluke area" anchor is disadvantaged, however you might get some purchase with a Bruce or Fisherman.

[/ QUOTE ]Of course we have tried it, and on the contrary, I would go with a Spade, Bügel, Delta, or Rocna. These anchors are designed to 'hunt' by the tip, and once they hook up on anything, they will transfer the force directly to that small point. A Bruce and Fisherman are quite capable of lying on their side and not hooking anything, since their dynamics do not work to force the tip(s) into the bottom. Witness Steve Dashew's recent comments on his Rocna, anchoring in the Pacific on exactly that type of bottom.

[ QUOTE ]
Possibly, perhaps my criterion is a bit high, >40m from anchoring point constitutes a drag and includes all drops - anchor will probably re-set, but that's not good enough if it's crowded.

[/ QUOTE ]I would say your criterion is too low - dragging any more than a few meters and the anchor, for one reason or another, is not doing its job.

[ QUOTE ]
Yes, that's when lack of hold usually occurs, but no way will the anchor ever hold at full revs in reverse, the screw is a Brunton 3-blader driven by a 3YM20. The winch is manual so I don't have that option, of tripping the cut-out.

[/ QUOTE ]21HP correct? You shouldn't be able to drag your anchor in fair holding. Reversing the prop while stationary, most sailboats are unable to simulate wind conditions greater than 30 knots or so. Of course the exact figure depends on the boat. If the anchor is dragging just with your engine and you are unable to ever get it to hold, something is wrong.

[ QUOTE ]
The boat is very wind-rode and sails freely up to and round her anchor unless it's blowing >F4. A long scope allows her to pick up sufficient speed to yank the anchor up.

[/ QUOTE ]That is a fair point. However, a boat "sailing" on her anchor is a whole other can of worms, and is a problem that can be alleviated. It does not justify recommending the use of short scope so directly detrimental to performance of the anchor.

[ QUOTE ]
What I try to do is find a mud bottom, choose the deepest point and drop the hook in there. The problem is that mud bottoms are few and far between in the Central Med, though the Adriatic is better. Drags occurs on thin sand on rock or pebbly bottoms or when the anchor gets something on its point.

Nice flat bottoms, like mud are few and far between, so by definition one is frequantly anchoring on a slope. If it isn't it's usually rock.

[/ QUOTE ]Since we're talking about the Med, why are you using a CQR? All the problems you describe are characteristic of it. Consider the recent popularity of the Bügel and Spade. Consider the recent SAIL and Yachting Monthly testing, which illustrated the differences that become apparent when the anchors are asked to set in more difficult seabeds, such as hard sand.

Try a different anchor - and use a bit more chain. Your will find the problems you seem to perceive as unavoidable will disappear.