A contradiction with bigger anchors

[NormanS]

Another rerun for a Neeves peeves

And not really on solid ground imho, is there really a recommendation for the majority of boats people on here sail, weekends out and a week or three in the summer to go a size or 2?
Don't think there is and wandering round marinas it's seldom you see a biggie. And even if you do it's often on a boat obviously more used to being on the move and living on the hook. Where the practice is commonplace and recommended by many extremely experienced cruisers is on a long term long distance boat. With regards to chain strength etc, in general these are people well versed in keeping the boat going and more than capable of reading data sheets along so that's not really a big deal. Also keeping the anchor loads down with various strategies / snubbers etc takes the strength argument largely out of it.

So do many weekend sailors go big? Can't be many, you never see them.

Quite a few contradictions there.
If you want to see the anchors used by serious users of anchors, a marina is probably not the best place to look.
By definition, long distance sailors spend long times on passage. Coastal cruisers, unless they are pontoon hoppers, anchor much more often, so are just as likely to have as much experience of anchoring. I have never done an ocean passage in my life, and have no desire to do so, but I anchor every night.

 

[GHA]

Quite a few contradictions there.
If you want to see the anchors used by serious users of anchors, a marina is probably not the best place to look.

Exactly. The "get a bigger anchor" just isn't common advice or recommended for most forum users.

 

[Neeves]

When you say 'size' are you using that interchangeably with 'weight'?

I'm being careful to be vague as I did not want to go down that track. Most people's idea of size is weight, that is generally how they are sold. Many people also think a 10$ increase in weight means a 10% increase in hold - I think that erroneous - which is why I've left it vague. I agree with the very simplistic view that a larger anchor has the potential of having greater hold.

Sticking with an engine and windage. If you have a 20kg anchor and a 30kg anchor and your engine power can develop a tension of 300kg then the maximum hold of both of those anchors is 300kg. If the wind develops and increases the tension to 500kg then the maximum hold of those 2 anchors is 500kgs. The bigger anchor will develop no more, nor less. hold than the smaller one. The difference between the 2 anchors will be that to achieve the same hold the smaller anchor will have dived more deeply (you can decide which is better, if any, a deeper set or shallow set anchor). The larger anchor will only develop more hold when the smaller anchor has achieved its maximum diving depth - which might be, in that seabed, 1,000kg and in most good seabeds - 2,000kg. In thin mud neither anchor may achieve any hold.

The idea that a larger anchor develops more security than a smaller anchor in most recommended anchorages is a good way to improve anchor sales. I suspect if we had access to the data this could be proven. There is no evidence from members here that have the recommended sized modern anchor that they wish they had gone bigger.

Jonathan

 

[Neeves]

Another rerun for a Neeves peeves

And not really on solid ground imho, is there really a recommendation for the majority of boats people on here sail, weekends out and a week or three in the summer to go a size or 2?
Don't think there is and wandering round marinas it's seldom you see a biggie. And even if you do it's often on a boat obviously more used to being on the move and living on the hook. Where the practice is commonplace and recommended by many extremely experienced cruisers is on a long term long distance boat. With regards to chain strength etc, in general these are people well versed in keeping the boat going and more than capable of reading data sheets along so that's not really a big deal. Also keeping the anchor loads down with various strategies / snubbers etc takes the strength argument largely out of it.

So do many weekend sailors go big? Can't be many, you never see them.

Strangely GHA I had a thread on modern anchors dragging (about 6 months ago) and I specifically asked about anchor size and size related to anchor chart sizing tables. From memory I would say half the respondents said they had an anchor one size larger and some 2 sizes larger than recommended. A large minority had the size recommended and a few had anchors smaller than recommended. I fully accept the replies do not form statistically sound evidence. The conclusion from the thread was that evidence of modern anchors dragging was lacking, whatever size, except when they became entangled in a supermarket trolley.

Whenever I read forum threads of persons requesting advise on anchor choice (including here) then always, without fail, at least one person, if not many say - go bigger than the recommended charts. If you read Noelex posts with just a little care - that is his advise. This is despite advise suggesting, specifically Rocna, have already upsized their chart. The other suggestion is go as big as is possible for actual housing on the bow roller and the size of your windlass. Some people even advocate doubling the size of the anchor, over the size suggested in the anchor charts. In fact if my memory serves me well - you have just bought an anchor bigger than that recommended, why did you buy the bigger anchor, because if somehow its going to produce more hold then maybe you should have upgraded the rest of the ground tackle to accommodate that extra and anticipated load.

So my thought was simple - if the chart says 20kg anchor for your yacht and you buy a 30kg anchor (and this does not seem an unusual 'upgrade') - why not upgrade the chain, swivel and shackle as well. Why do you expect the extra hold not to impact the other components in the rode? There is no evidence of chain damage as a result of a larger anchor though there is evidence of chain stretch (which might just be poor chain). There is evidence of both swivel and shackle failure, in fact it is surprisingly common - again this might simply be poor choice. But if you are focussing on security why is it then limited to the bigger anchor, a better shackle is hardly expensive. Yet I hear of more shackle failure of people with modern anchors and never hear of modern anchors dragging (except when they are caught in crab pots and the like).

For many who only anchor for lunch this will have no interest whatsoever, like many threads on this forum, but for those who anchor overnight with their children or grandchildren, use their yacht for an annual 2 week holiday or live on their yacht for 6 months a year - and surely there are 1 or 2 in this category - I thought it an interesting topic to discuss.

Sorry that you feel the need belittle

Jonathan

 

[Neeves]

The focus on a larger anchor is often just on the improved holding capacity but in practice the ability to anchor in poorer substrates or at shorter scopes is a valuable bonus.

It opens up anchorages that would otherwise not be viable, or perhaps not deemed suitable for overnight.

It is a matter of degree, rather than absolute difference, but anchoring overnight (hopefully safely) and enjoying a peaceful sunset while some boats are forced to leave for a more "suitable location" is a nice advantage.

A larger anchor is by no means immune from dragging so it is important to excersise some judgment, but it does extend the viable anchorages (compared to an identical smaller anchor) for any given conditions.

GHA, just an example, there are many others from other people - Noelex is not advocating anything new.

 

[Robin]

I've stayed away this time but my assumption always has been that quoted weight is merely an indication of size and since a simple weight alone doesn't work that it is the working area which is important. I went up from a suggested 35lb to a 45 lb on revamping our set up ( Delta on all 10mm/3/8" chain) and even then the 35lb was actually rated for ('up to') a bigger boat. I had an undersized 35lb one on a 41 footer that served fine for 10 years and 20,000 miles so the 45 lb one on a 36 footer should be just fine and dandy and indeed is so far.If weight alone counted a Fortress would not work so well. Probably a diversion but thought I would chip in my 2 cents.

I'm still waiting to hear reports of how one of the new gen anchors held a supertanker in a cat 5 hurricane as might be implied by their advocates but nobody so far ever admits to going for a lighter version than might be considered 'normal' for their boat or did they not live to tell the tale perhaps?

 

[Neeves]

Much to GHA' annoyance I am still here and we use(d) a 15kg steel Excel as primary on a 38' x 7t cat. We have since swapped the steel version for the alloy version (but same physical size) which weighs in at 8kg. Our cat has the windage, simply addition of front and side elevations, as a 45' AWB though it would weigh around 12t/14t. We used the steel Excel for 5 years and the alloy, as the primary, now for only 6 months (without any issues). The strongest winds we have been subjected to, measured at the masthead, has been 55 knots (steel Excel) - we are still here. There are a few other forum members with an anchor one size smaller than the charts might recommend - but we are a minority.

Without encouraging thread drift - evidence suggests that if you can get an alloy Spade or Excel to work (to set - and we have never had an issue) then they have the same hold, or as similar as makes no difference, to their steel counterparts. Its more difficult to quote Fortress vs Danforth as they are not exact copies but all tests seem to suggest that anchors of similar size perform similarly, or that the Fortress is better. Possibly simplistic - but weight is not relevant - its physical size, or area.

I know a size too small simply does not work, I've tried a 5kg Spade and separately 5kg Excel, complete waste of time, even for lunch. But no-one will be surprised by the result We do know that our anchors are too small for thin mud, they simply drag (been there, done that). The Fortress Chesapeake tests seem to suggest we would need anchors 3, 4 or 5 times bigger to have any security - its easier just to use a Fortress than carry something 'that' big.

Jonathan

 

[rgarside]

There's a lot of data on full size anchors, plus behaviour of mooring lines, etc here:-
http://vryhof.com/flipbooks/am2015/#

You'll need to scale down a bit to get to yacht size anchors, but there are some factors for variation of holding capacity with weight in the manual.

 

[Neeves]

Another contradiction.

We have chosen to follow a different path to many and have gone the small and quality route

So we have an anchor that some might consider too small - though it has proven perfectly adequate in some testing conditions.

But and a big but.

Smaller anchors are designed for small yachts and hence smaller potential loads. Consequently if well set in strong winds using a larger yacht than that for which the anchor is designed then the anchor is potentially at some risk to bending - or in our case we might be testing the edge of the strength design envelope.

So, unlikely though it might be be - anyone fallowing our lead should be conscious of all the decisions and thought processes we have gone through.

The corollary is also true - if you considering an anchor whose strength you might query, not mentioning any names, then having one bigger than the anchor maker recommends means it will be stronger (and maybe one reason. why some anchor makers recommend larger anchors than others)

rgarside, Vryhof is a great background source as are some of their and Bruce' research or technical papers given at 'oil' conferences.

Jonathan

 

[lw395]

I've used a big Fortress in poor holding where others were dragging in pretty benign conditions, so I can see the attraction of a big anchor.
Over-speccing the chain adds a lot of weight where you don't want it.
I don't know anyone who has broken an anchor chain.
In the limit, something will always break, maybe I'd rather it was the chain than pulling the bow off the boat.

I have heard tales of the chain getting stretched in extreme conditions, but that's a fair way from breaking it.
I think if you get caught out in a hurricane and your chain will never run smoothly over the gypsy again, you should probably buy a new chain with good grace and be more careful in future?

FWIW, I once bent a Danforth after getting it well wedged in rocks.

 

[Neeves]

You do not need to buy bigger chain for it to be stronger. G40 instead of G30 etc.

Once it stretches it will, eventually, not fit the gypsy and then to 'save' the anchor you will need to pull it all in by hand, easy with 6mm or 8mm - slightly more taxing with 10mm or 12mm. Is taxing quite the right word.

Jonathan

 

[lw395]

I suggest you read Jonathan's article on chain in the current Sailing Today, and maybe attend one of my anchoring talks, RYA and CA have hosted several recently. Catenary at fresh winds and above is effectively non-existent, also as calculated by Alain Fraysse some years ago. I show a large number of photos that demonstrate quite conclusively that all of the chain lifts of the bottom in winds of F6-7. One of these is of a 27 kg Manson Supreme with 12 mm chain attached to an Oyster 55. Even this extremely heavy chain, about 25 metres with a scope of 4:1, was fully clear of the bottom in gusts.

I also show the graph of results of the 2006 YM anchor tests. All anchors were 35 lb models. In a variety of bottoms Spade, Rocna and Manson Supreme all held at over 2 tons load on 3 out of 4 pulls. I cannot imagine that my deck fittings would hold this much, although my 8 mm chain certainly would.

Anyone who's been on an anchored boat yawing and reacting to even small waves should realise that the Fraysse analysis of catenary effect is woefully simplistic.
The mass of the chain gives it inertia as well as weight.
As it is dragged throught the water it gives some damping.
A lot of variables in the real world, regrettably too much for articles in our glossy comics.

'Fully clear of the bottom in gusts'
That means it has allowed the boat to move back in the gust, absorbing some energy. Maybe it doesn't bode well for Force 10, but it will be reducing the peak loads and making life better onboard in the F6/7.

 

[lw395]

You do not need to buy bigger chain for it to be stronger. G40 instead of G30 etc.

Once it stretches it will, eventually, not fit the gypsy and then to 'save' the anchor you will need to pull it all in by hand, easy with 6mm or 8mm - slightly more taxing with 10mm or 12mm. Is taxing quite the right word.

Jonathan

When I can afford a yacht that will stretch 12mm chain, I will have staff to bring me a fresh chain when required....
I'm more likely to be using 12mm nylon.

 

[Richard10002]

I've only read the first 3 pages of this and keep coming back to the thought that the anchor, and the chain, have no idea what type of boat they are connected to, nor how heavy it is. They only know what the pull on them is, along with the direction.

Given that the "weight", (for want of a better scientific word), on the anchor, and the direction of pull, increase and deteriorate, respectively, as conditions worsen, surely there comes a point where, no matter what the type or weight of the boat, the heavier/bigger anchor will perform better than the smaller anchor.

The alternative to my laymans conclusion is that the performance of a heavier anchor will deteriorate in more benign conditions?? which is not something that is ever postulated, provided that the boat and its engine or sail power is enough to dig the anchor in to a reasonable level, e.g. a 10 tonne anchor on a 10 tonne boat would be ridiculous, unmanageable, and definitely undiggable

I agree that, in these hypothetical worsened conditions, if the anchor is so big, and so effective, there could come a point where the tension or snatch will be such that the chain stretches of breaks - but I thing it has been suggested that deck fittings and the boat itself may have given up before the chain does.

In a laymans way, I often think in a similar way about different things, i.e. "the anchor has no idea what it is attached to, merely the effects it experiences at its point of attachment to the shackle and chain.

 

[lw395]

I've only read the first 3 pages of this and keep coming back to the thought that the anchor, and the chain, have no idea what type of boat they are connected to, nor how heavy it is. They only know what the pull on them is, along with the direction......

But if the pull and direction are not steady, the anchor is stopping a mass every wave. A light boat will have a different variation of 'pull' than a heavier one.
I don't believe an anchor will fail to work because the boat is too light though.
It would have to be pretty convoluted circumstances surely?

 

[Richard10002]

But if the pull and direction are not steady, the anchor is stopping a mass every wave. A light boat will have a different variation of 'pull' than a heavier one.
I don't believe an anchor will fail to work because the boat is too light though.
It would have to be pretty convoluted circumstances surely?

The issue must be to do with the point at which an anchor will fail to do its job, for some reason, and I'm guessing that this will be the point at which it will either drag, or break up, or something else I cant think of.

Presumably, the forces imposed by a "smaller" boat in heavier winds, or bigger waves, causing bigger snatches or a bigger constant pull, could be/will be, the same/similar to those imposed by a larger boat in lesser conditions - albeit, at some level, both could be the point at which a particular anchor type/size fails in one way or another

My laymans conclusion remains that a bigger/better anchor on the smaller boat will enable it to survive worse conditions.

Clearly, once you have specified an anchor to withstand a particular level of conditions, (or whatever), you then need to ensure that the chain and deck fittings can withstand them - which was the OPs point in the first place.

I agree that an anchor wont fail because the boat is too light, or the anchor too heavy - which was one of the the points I was making. i.e. that an anchor cant be too heavy, (unless it is so heavy that it is unmanageable or undiggable).

 

[lw395]

....

Presumably, the forces imposed by a "smaller" boat in heavier winds, or bigger waves, causing bigger snatches or a bigger constant pull, could be/will be, the same/similar to those imposed by a larger boat in lesser conditions - .....

You might choose to presume that, I question it. But I don't think it is a real world issue TBH.

 

[lw395]

The issue must be to do with the point at which an anchor will fail to do its job, for some reason, and I'm guessing that this will be the point at which it will either drag, or break up, or something else I cant think of.
....).

Maybe the 'something else' is a light boat being more likely to foul an unburied heavy anchor when the tide turns?
That's the only thing I can think of at the moment.....

 

[geem]

'Fully clear of the bottom in gusts'
That means it has allowed the boat to move back in the gust, absorbing some energy. Maybe it doesn't bode well for Force 10, but it will be reducing the peak loads and making life better onboard in the F6/7.[/QUOTE]

Not my experience. Gusts in the 25-30 kts range in shallow water with 4:1 scope with a well set anchor can be very uncomfortable. The chain can lift off the bottom very quickly and create a considerable snatch due to the relatively short length of chain and lack of weight. A very long snubber line and an over sized rubber snubber make a huge difference but that 10mm chain is totally straight. We now use a three strand snubber line that is half the length of the boat (44ft boat). The fairly recent addition of the large rubber snubber to this line has made a considerable difference.
If we anchor in deeper water we don't get the snatch in this kind of gusty weather which would suggest we are not straightening the chain at these wind strengths. So deeper water in better for comfort as the weight of chain is useful.. We have found this true up to gusts of circa 40kts. We have not needed to anchor in stronger winds.

 

[Neeves]

People have made the observation that yachts veer and then snatch as they sail at anchor. When this occurs the anchors is being constantly loaded in different directions, I've measure veers of 75 degrees and in one specific anchorage have veered through 180 degrees. When an anchor is loaded at constantly changing directions it leans over, but does not set more deeply. Conversely if you snatch load, or evenly load, an anchor in one direction it sets more deeply with each tug (or steady pull).

If a lightweight yacht with a small engine sets an anchor, maybe a bit too big for it then the engine will not set it deeply. If the wind picks up and is not in a steady direction then whatever set has been developed has every chance of being negated by the constant veering of the wind (for which light yachts are prone).

If the anchor was deeply set, with the shank and chain well buried, it will be more stable because the shank will not lean (leaning is resisted by the seabed in which it is buried) and the buried chain has to be dragged through the seabed and reoreintated inorder to impact the shackle.

If you had 2 anchors set in a 'V' each will only be loaded in the set direction.

Jonathan