Anchors - Bigger is Better ?

[cwyckham]

Good summary, Jonjo.

I love my Boss, but I, too, upsized when I switched.

[Alan Mighty]

Originally Posted by JonJo

Virtually all of the comments were subjective as no-one, reasonably, had set a lighter anchor in 50 knots of wind and when it dragged set an identically designed anchor 2 sizes bigger - and not dragged.

The use, or popularity, of bigger is better has no restrictions in terms of seabed - it is believed better in soft, hard, muddy and weedy seabeds.

It was difficult to judge whether the comments that bigger is better was based on a generalisation (go to the next sized anchor bigger than recommended) or go for 2 sizes bigger which was the basis of the original question.

But reiterating

The concensus was that a bigger anchor is, without any shadow of doubt, better than a smaller one.

What have I missed?

Jonathan

If you can tolerate the comments of newbie late to the table (and who would like to say "more, please sir") ...

I think your summary was accurate and fair Jon. I hoped the thread had gone further and I think your summary could have fingered some of the weaknesses of the thread.

Specifically:

1. A rigorous discussion and definition of what a "standard" anchor is. That could have started, for instance, with Professor John H. Knox's "Force 5" guideline, that a "standard" anchor should hold a boat in F5 winds.

2. A rigorous evaluation of what "bigger" means in these days of new generation anchors alongside a considerable installed base of old gen anchors. That might for instance have involved mentioning guideline such as van Dorn's that holding power was directly proportional to fluke area (but also associated with shank/fluke angle and the sharpness/tendency to penetrate of the flukes and that fluke area for much affordable metal fabrication was associated with mass^(2/3).

3. A rigorous evaluation of what "better" means. That might have for instance started with your own published observations (dating back to 2008 in Afloat, unless I'm mistaken - those not familiar with your work can browse the back issues at afloat.com.au) quoting and quantifying maximum holding capacity in kg.force/kg mass.

4. A rigorous evaluation of the dis-benefits of "bigger". That might have for example involved the effects on a sailboat of having one or more heavy chunks of metal sitting on bow rollers. And at least some of that dis-benefit is directly proportional to the product of that mass * (distance of that mass from the Centre of Gravity of the rest of the boat)^2.

Without something on those lines, I consider the thread to date to be a FAIL. And I think you captured that failure, noting the subjective nature of contributions and the generality of them all.

Al (who just discovered the Edit button! A newbie excuse)

[Alan Mighty]

Originally Posted by Alan Mighty

4. A rigorous evaluation of the dis-benefits of "bigger". That might have for example involved the effects on a sailboat of having one or more heavy chunks of metal sitting on bow rollers. And at least some of that dis-benefit is directly proportional to the product of that mass * distance of that mass from the Centre of Gravity of the rest of the boat.

And of course that should read "dis-benefit is directly proportional to the product of that mass * (distance of that mass from the Centre of Gravity of the rest of the boat)^2.

Is there nae an 'edit' button to correct typos?

Al

[Pirate999]

I go with the bugger is better theory. My boat carries an oversized cqr on the bow. Given the size of the boat, weight is not an issue. I also have 400' of chain.

But the story is with the previous owner. He carried, and I still have, the mentioned cqr as well as a regular sized danforth and a large danforth along with a huge collapsible fisherman. The large anchors were all stowed. My understanding is that he went through two cyclones with his large anchors and didn't have a problem.

[sailorboy1]

Originally Posted by cwyckham

I love my Boss, but I, too, upsized when I switched.

Took me a moment remember you were talking about anchors as I was wondering what type of job you had

[Andrew Troup]

Originally Posted by noelex 77

....
One area where the new generation anchors have not improved over there old counterparts is performance on short scope.
The Bruce Anchor has always been regarded as exceptionally good on short scope. Its geometry is very different to most anchors so it is no surprise that it has different properties.

One caution I would add is that the Bruce is very size dependent. Large Bruce anchors (say 40kg +) seem to work much better than small versions.

The general consensus seems to be that the Spade works poorly on a short scope, but I did once see a spade holding a boat in 35-40 knots on a very short scope. The shank was lifted a long way off the bottom. I was very impressed, but it was an isolated incident. Overall I think the evidence is that the Spade is not great on a short scope, but I still have an open mind.

I stumbled across this when looking for something else, but on the principle that you can never have too many anchor threads (even ones with almost identical names )

here's what sprang to mind:

There's a risk of circular logic taking hold in certain subcamps of the NewGen anchor movement, it seems to me.

Here's one way it might play out for someone who frequents deep anchorages:

<< I got rid of my 40kg Bruce because NewGen anchors hold better.
And I got rid of my heavy chain, so I can carry a longer length of smaller chain.

So now I have a 40kg anchor and a longer chain. Same weight overall.

However in anchorages deep enough so I previously had all my chain out, I STILL have all my chain out, but even then my anchor is occasionally not holding like the old one did, because:

I no longer have sufficient catenary curve to improve the apparent scope the anchor 'sees', and my new anchor doesn't hold as well at short scope as the old one did.

What's more, my swinging circle is much larger. And my smaller chain is jumping the smaller teeth on the new chainwheel when my anchor digs for China; so at times now I have to faff around with chain hooks and the motor just to get my anchor back after an overnighter in normal conditions.

[JonJo]

Andrew,

Trying to keep two similarly named threads apart

The concensus is that one discards the, say, 40kg Bruce (which was the correct size (based on an average of sizing charts)) and replaces it with a new gen anchor of at least the next size up (even better - 2 sizes up). The replacement would then be, say 55kg.

So the 40kg Bruce is replaced by, say a 55kg Supreme or a 55kg Spade.

The concensus of the thread was - that's the way to go.

This does not negate your comments (either for a 40kg or 55kg replacement) with regard to chain. However the idea of the thread, and one similarly named, was to deal with one issue at a time.

If there is any merit in a 'stronger' smaller chain (so its lightweight) then it might be possible to have another thread trying to combine the 2 issues, 'bigger anchor and lightweight chain'. This is the thesis proposed by a number of respected yachtsmen.

The main argument being that at windspeeds above 30 knots (might be 35knots) the chain is as straight as a snooker queue anyway - so why carry a heavy chain to provide catenary when the catenary disappears just when you need it most.

However in the absence, yet, of a single advocate with a strong technical argument in support of a lightweight, strong, chain it does seem that a third thread is unlikely I await the development of the 'second' thread to see how that pans out.

But I'm not sure that a chain hook is particularly difficult to attach and the snubbers to which the chain hook is attached look to offer advantages whatever weight of chain you use (and even more so if you have a multihull - where you use a bridle, with chain hook, every time you deploy the anchor - maybe multi owners are more tolerant?).

Jonathan

[Andrew Troup]

JonJo

The thread having run its course, my post was aimed at raising a narrow point, flowing from Noelex's interesting post I quoted, rather than being intended to illuminate your (ie the OP's) topic.

Didn't seem a big enough point to deserve a new thread. It's specific to one brand of anchor which is no longer even available new, and the point is specific to deep anchoring.

In the latter connection, even Smith and Fraysse both acknowledge that catenary from heavy chain is a major factor in DEEP anchoring

not just for snubbing, but for direction of pull (ie scope as "Perceived" by the anchor)

And it struck me that deep anchoring is presumably a major reason for people wanting to carry longer, lighter, chain. It's certainly why John Harries went to G70 (to my considerable surprise). And IIRC he favours a Spade ....

- - - -

I mentioned the chain hook in connection with a hypothetical problem breaking out a NewGen anchor on a light chain.

In a situation where, with an old school windlass and heavy chain and moderate digging anchor, getting the anchor would simply involve stopping the windlass when 'up and down' and motoring ahead, (possibly all controlled from the cockpit)

a small chain on a deeply embedded anchor might require going to the bow, fitting a (second?) chain hook on a short, non-stretchy strop, then releasing the windlass clutch, going back to the cockpit and motoring judiciously ahead for a period, to extricate the anchor. Not a deal breaker, but a consideration.

[JonJo]

Andrew,

I understand your point, now - but you were suggesting initially that the combination you were considering (light chain and Bruce) would result in the anchor not setting, now you are suggesting (I think) that the anchor might set so well (I assume you are now thinking of the new gen) it would be difficult to retrieve (so much so you are suggesting you would not want that load (I'm sure not an accepted technical word) imposed on the windlass.

I do not think that this problem is restricted to lightweight chain - sit out really strong winds and new gen anchors can set so deep they can be desperately difficult to break out and give a little bit (or worse a lot) of chop and you have snatch loads of ferocity once you get to the near vertical on retrieval. I suspect more anchors are damaged on retrieval than 'in use'. Thin chain will, of course, engender a more deeply set anchor.

Its a compromise, again. If your anchor sets well then you must expect that if you load it up over a period of time then it will be well set - better than an anchor that does not set - methinks?

You also introduce the contradiction that Noelex says a Spade does not 'hold' at short scope (or too large, high, a chain angle) and that with a lightweight chain the angle will be high (because there is less catenary) but one of the advocates of the light chain uses a Spade.

Personally, having used one many times, at a variety of scopes I find the Spade performs well at short scopes - but I confess never to have tempted fate and deliberately anchored with a short scope in 35 knots of wind or more. To find oneself anchored in 35+ knots at short scope looks like incompetence or very, very bad luck.

Jonathan

[noelex 77]

Originally Posted by JonJo

You also introduce the contradiction that Noelex says a Spade does not 'hold' at short scope (or too large, high, a chain angle) and that with a lightweight chain the angle will be high (because there is less catenary) but one of the advocates of the light chain uses a Spade.

Personally, having used one many times, at a variety of scopes I find the Spade performs well at short scopes

Despite the comment I think the steel Spade is a great anchor. All anchors have reduced holding power at a shorter scope.

The table produced by Fortress (Fortress Anchors – The World's Best Anchors! – Safe Anchoring Guide ) is I think pretty accurate for most anchors at average anchoring depths:

Scope Percentage holding power
2:1 10%
3:1 40%
5:1 70%
7:1 85%
10:1 100%

The above Fortress percentages apply roughly to all anchors (although some feel up to 14:1 produces some slight improvement over 10:1), but some anchor designs do slightly better than others.

It is interesting that this is an area where modern new generation anchors have not improved over their older counterparts.
I think the king of the short scope anchors is the old generation Bruce. If you have to anchor at say 2:1 a big Bruce is very hard to beat.

The steel Spade is great anchor, one I would be happy to have on my bow, but compared to its counterparts it is slightly more sensitive to scope.

The large Sail and Yachting World magazine anchor test of 2006 concluded the same thing for the steel Spade, reporting a fantastic performance at a 5:1 scope used for most of the tests, but noting a drop in performance compared to the other anchors at 3:1.

"Multiple pulls at both wharf locations yielded 5,000-pound load readings. Its simple weighted point and mid-sized blade easily penetrated and held without dragging. Results fell off dramatically, however, at 3:1 scope and at the New Brighton location."

Your anchor is an aluminium Spade has a different performance to the steel version. In harder substrates its performance is worse. (still a good anchor, but unfortunatly it looses the excellence of the steel version). It is possible that the relative performance for the aluminium version is more similar between long and short scopes.


I don't see any contradiction in someone carrying G7 chain with an anchor that may be slightly more sensitive to the angle of pull on the shank. On the contrary the most common reason for carrying HT chain is the ability to carry more chain to ensure a longer scope, so the combination makes sense to me.

[DoubleWhisky]

Originally Posted by Andrew Troup

Even Smith and Fraysse both acknowledge that catenary from heavy chain is a major factor in DEEP anchoring not just for snubbing, but for direction of pull (ie scope as "Perceived" by the anchor)

And it struck me that deep anchoring is presumably a major reason for people wanting to carry longer, lighter, chain.

Snubbing and direction of pull are important factors for Med mooring also, even when one does set his anchor in relatively shallow water. It make for less violent movements of boat in strong crosswind gusts and for less of periodical side forces on the anchor. So it adds both to the comfort of being aboard and to the good holding.
On the other hand - long chain is advisable for Med mooring, lighter chian much less

Regards

Tomasz

[JonJo]

[QUOTE=noelex 77;1527818]Despite the comment I think the steel Spade is a great anchor. All anchors have reduced holding power at a shorter scope.

The table produced by Fortress (Fortress Anchors – The World's Best Anchors! – Safe Anchoring Guide ) is I think pretty accurate for most anchors at average anchoring depths:

Scope Percentage holding power
2:1 10%
3:1 40%
5:1 70%
7:1 85%
10:1 100%

The above Fortress percentages apply roughly to all anchors (although some feel up to 14:1 produces some slight improvement over 10:1), but some anchor designs do slightly better than others.

It is interesting that this is an area where modern new generation anchors have not improved over their older counterparts.
I think the king of the short scope anchors is the old generation Bruce. If you have to anchor at say 2:1 a big Bruce is very hard to beat.

The steel Spade is great anchor, one I would be happy to have on my bow, but compared to its counterparts it is slightly more sensitive to scope.

end quote



I would like to see any reliable quantification of the idea that data produced by Fortress for their anchor applies to other new gen anchors. I have no doubts to the validity of the data with respect to the Fortress anchor but to extrapolate to other anchors is, I think, suspect. You might be correct - but I have never seen any evidence to support the contention. One pull, at the 3:1 scope, from the WM/YM/Sail test lacks any statistical validity.

I also doubt the comment that Spade are 'slightly' more sensitive to scope - having conducted numerous tests - sensitive does not come into any analysis - there are so many unquantifiable variables (the seabed 1m away - for example) that variables, in performance, have to be quite large to justify any conclusion.

But it is interesting that though there are 2 (different) anchors on the bow rollers of Morgan's Cloud the Spade is the primary anchor. This suggest that over a long period of time and experience the Spade had more than an edge - its definitely better.

Equally the idea that a 'big' Bruce might be better than more modern designs, again might be valid, but is totally irrelevant given that most yachts are less than 45' long, would not normally carry a big Bruce, of say 40kg or more and one cannot buy them anyway - primarily because very few people worry about the performance of an anchor set at a 2:1 scope. Equally the idea the big Bruce is better is 'subjective' (at a 2:1 scope) again - quantitative data would be better.



I have both an alloy and steel, an S80 and a A80 and have used them both extensively.

Jonathan

[noelex 77]

Originally Posted by JonJo

But it is interesting that though there are 2 (different) anchors on the bow rollers of Morgan's Cloud the Spade is the primary anchor. This suggest that over a long period of time and experience the Spade had more than an edge - its definitely better.

You can read Morgans Cloud's thoughts on the Spade verses the Rocna here:

Comparison Of The Strengths And Weaknesses Of SPADE And Rocna Anchors

It is worth noting that they also addressed the issue of the Spade performance on a shortish scope:

We can attest from our own experience that the SPADE is not great at setting in difficult bottom types on a scope of less than about 4:1 in relatively shallow water. (Interestingly, at least with a chain rode, the SPADE has no problem setting on 3:1 scope, even in rocky and weedy bottoms, once the water gets deeper than 75-feet.) On the other hand, everyone we have talked to with a Rocna says that it will reliably set on 3:1 scope in just about any bottom type and any water depth.

[Andrew Troup]

Originally Posted by JonJo

Andrew,

.... you were suggesting initially that the combination you were considering (light chain and Bruce) would result in the anchor not setting

Not so: The two scenarios I was comparing were Heavy chain & Bruce vs Light chain & NewGen.

Originally Posted by JonJo

now you are suggesting (I think) that the anchor might set so well (I assume you are now thinking of the new gen) it would be difficult to retrieve (so much so you are suggesting you would not want that load (I'm sure not an accepted technical word) imposed on the windlass.

Not exactly: I'm speculating that the smaller chain/chainwheel combo might become the limiting factor for the capability of the windlass to retrieve a deepset anchor, due to the small chain jumping the small dogs between chain pockets, in the extreme case of small (very HT) chain.

Originally Posted by JonJo

To find oneself anchored in 35+ knots at short scope looks like incompetence or very, very bad luck.

I'm saying that, in an anchorage whose depth is at the limit for the amount of chain carried, a boat which has switched to small chain could end up *effectively* at an unexpectedly "short scope", in strong winds, despite carrying more chain than it used to when it carried heavy chain.

Because in deep water, the catenary contribution of light chain to effective scope is minimal in comparison to heavy chain.

In a deep anchorage, a calculated scope of 2:1 could easily provide 5:1 effective scope at the anchor, PROVIDED the chain is heavy.

So I'm trying to highlight a perverse and counterintuitive result, whereby a person switches to light chain in order to carry more, so they can anchor in deeper situations. As John Harries has done.

Yet it seems to me conceivable that such a switch could actually end up impairing the ability to anchor in deep, windy situations.

If this is true, switching anchors at the same time, to one less tolerant of high shank angles, would compound the impairment.

[cwyckham]

Catenary has been much discussed. Many of as feel it is useless since it is gone by the time you have a big enough blow to drag the anchor.