Anchor chain scope

James_Calvert said:
Point of detail, my recollection is that 3: 1 was the rule of thumb for fisherman anchors.
4:1 became recommended for more modern anchors like the CQR.
When the Bruce became available, it was marketed as one that worked on a shorter scope.

And scope was measured at sea level. You let the anchor out until the relevant marker was submerged. If the wind blew up you let out some more until it was again submerged. And to the next marker for luck, maybe.
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What are these markers to which you refer?

Modern cats, like a Lagoon have a high freeboard, I'd think nearer 2m. With your recommended 4:1 for a CQR that means deploying a 14m rode (with less for your idea of a Bruce) with a 3.5m depth. 4:1 might have been an acceptable rode, but I doubt it, 50 years ago - with smaller yachts

I think not - unless its lunch only.

Ours is a 38' cat, less freeboard than the current production cats - at 3.5m depth - assume no tide, good forecast - I'd deploy 25m of chain minimum (and because our chain is marked at 10m intervals - my wife would deploy 30m). If we had only room for 25m - we would go somewhere else. If its that crowded we would move - and often have. Too many idiots trying to squeeze into a small space results in people using stupidly short rodes which simply don't factor for an error in the weather - forecasts are not a certainty. We sail as enjoyment and crowded anchorages at best are noisy and worst mayhem.

Jonathan
 
I read Jonathan’s post re reverse catenaries with interest and was aware of this phenomenon. I believe it is particularly pertinent to very deep anchoring of drilling rigs/FPSOs etc with composite and very complex rode systems. Clearly it also relevant to smaller anchors. But when it comes to determining scope for a leisure yachtsperson I’m not sure I would consider it. All you need the rode to do is transfer the tension to the anchor without breaking the anchor out and long enough to dampen peak tensions to ensure a night without being tumbled out of bed or spilt milk (or beverage of your choice). Since it would appear most modern anchors need quite a steep (much greater than 3:1) rode to cause breakout and since few if anyone would be comfortable with a scope of less than 3:1 the key is load damping. Then you open the Pandora’s box that is rode design!

so to answer the op 3:1 is enough providing the conditions are reasonably benign and with a short length ofchain and plenty of nylon, probably sufficient for quite a blow
 
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NormanS said:
I'm fairly sure that what Johnathan writes at length is technically correct, but his long and detailed essay, which I have skimmed through looking for relevance, has the effect of making a simple subject seem much complicated than it really is.
Imagine someone new to anchoring trying to digest all that. They would probably decide that it was too much hassle, and choose to go to a pontoon or a mooring.
The amount of scope required is not an exact science. It used to be generally accepted that 3:1 was a reasonable figure. It seems now that with more modern, but not necessarily better, anchors, 3:1 is not enough, and 4:1 or 5:1 is needed. Try to get your head round that anomaly.
I would suggest that 3:1 is fine in deep water, but maybe 5:1 or even more in shallow water. It depends on many other factors, including whether you have an all chain rode, whether the anchorage is sheltered from waves, wind or current, the type of material on the seabed, and the strength of wind expected. Too many variables to give an exact figure, but that's it - it doesn't have to be an exact figure. Just go out and do it and learn.
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I find it incredible that with weight of evidence from numerous independent tests of various new generation anchors that you cannot accept that they are far better than old generation anchors. New gen anchors generally need less scope. Not the conclusion you come to.
They set far better and hold more reliably. This is not controversial. It's known fact based in weight of evidence. Based in my own experience gained over many years where I previously owned Bruce and CQR anchors, there is no comparison with my Spade anchor. The Spade is fantastically reliable. Something I never experienced with a CQR or Bruce anchor.
Take off the blinkers see the light
 
boomerangben said:
I read Jonathan’s post re reverse catenaries with interest and was aware of this phenomenon. I believe it is particularly pertinent to very deep anchoring of drilling rigs/FPSOs etc with composite and very complex rode systems. Clearly it also relevant to smaller anchors. But when it comes to determining scope for a leisure yachtsperson I’m not sure I would consider it. All you need the rode to do is transfer the tension to the anchor without breaking the anchor out and long enough to dampen peak tensions to ensure a night without being tumbled out of bed or spilt milk (or beverage of your choice). Since it would appear most modern anchors need quite a steep (much greater than 3:1) rode to cause breakout and since few if anyone would be comfortable with a scope of less than 3:1 the key is load damping. Then you open the Pandora’s box that is rode design!

so to answer the op 3:1 is enough providing the conditions are reasonably benign and with a short length ofchain and plenty of nylon, probably sufficient for quite a blow
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Its good to know someone relates to the concept.

Its used in more shallow moorings - shackle angle is calculated by the US Navy when developing fleet moorings.

I'm not suggesting we would use the angle (we cannot measure it :( ) I was simply attempting to point out that the 3:1 or 6:1 relates to an angle and people are fixated with the idea that anchors are best tension with rode on the seabed, thus tensioned a 0 degrees. because modern anchors bury the shackle - the tension angle is never 0 degrees - but something higher.

I may have been a bit parsimonious with my script - but a member here complains bitterly about the length of my prose and I try to accomodate all tastes :)

Jonathan
 
Neeves said:
Its good to know someone relates to the concept.

Its used in more shallow moorings - shackle angle is calculated by the US Navy when developing fleet moorings.

I'm not suggesting we would use the angle (we cannot measure it :( ) I was simply attempting to point out that the 3:1 or 6:1 relates to an angle and people are fixated with the idea that anchors are best tension with rode on the seabed, thus tensioned a 0 degrees. because modern anchors bury the shackle - the tension angle is never 0 degrees - but something higher.

I may have been a bit parsimonious with my script - but a member here complains bitterly about the length of my prose and I try to accomodate all tastes :)

Jonathan
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In the past have fallen into the trap of the 0 deg seabed angle but of course is not relevant to modern leisure anchoring. The interesting point with this is that there is a huge amount of technology and expertise in modern anchor and rode design that has enabled exploitation of seabeds and beneath. It has inevitably filtered down to the leisure market in the form of anchors, but the maths has been left behind. After all, the software is expensive, relies on detailed knowledge of the seabed and of course imparted loadings, none of which is generally available. Plus each anchor location in industry is a discrete case. on a small boat there is limited scope (excuse the pun) for carrying multiple rodes for each anchoring scenario, so the all chain rode “good enough for ships, good enough for my little ship” thought process. I guess there are advantages to an all chain rode, but in my book, nylon and 5m of chain gives a peaceful nights sleep and easy workout in the morning. I just rely on my 3 (and ok sometimes 4) times table to do my rode design.
 
James_Calvert said:
Paint of course!

( Colour/banding to the code of your choice.)

Or knotted cord, or spinnaker material ribbon, or cable ties.

Or tape recovered from your cassette player?

Subject of another thread already perhaps.
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I perhaps was being obtuse.

You said

quote "You let the anchor out until the relevant marker was submerged. If the wind blew up you let out some more until it was again submerged. And to the next marker for luck, maybe." unquote.

It was the submerging bit that got me - we simply watch the marks pass the bow roller, finish. In the dark we would not see ours disappearing into the gloom without using some yoga moves to peer over the bow (as our bow roller is well beck from the crossbeam). and if the rode was straining under the wind (necessitating that extra rode - then the marks would be well forward).

Sorry to be such a pedant. :)

Jonathan
 
boomerangben said:
In the past have fallen into the trap of the 0 deg seabed angle but of course is not relevant to modern leisure anchoring. The interesting point with this is that there is a huge amount of technology and expertise in modern anchor and rode design that has enabled exploitation of seabeds and beneath. It has inevitably filtered down to the leisure market in the form of anchors, but the maths has been left behind. After all, the software is expensive, relies on detailed knowledge of the seabed and of course imparted loadings, none of which is generally available. Plus each anchor location in industry is a discrete case. on a small boat there is limited scope (excuse the pun) for carrying multiple rodes for each anchoring scenario, so the all chain rode “good enough for ships, good enough for my little ship” thought process. I guess there are advantages to an all chain rode, but in my book, nylon and 5m of chain gives a peaceful nights sleep and easy workout in the morning. I just rely on my 3 (and ok sometimes 4) times table to do my rode design.
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I would totally agree

except, there are always exceptions.

Here the ambition of many is to visit The Reef, which was our ambition until we discovered how many had the same idea at the same time. Sadly it is a little known but undeniable fact that inanimate coral actually has a voracious appetite for nylon - it will consume a rode, or a bit of it, overnight. Consequently we are all a bit parsimonious and object to feeding the coral with its preferred source of fibre and use all chain. There must be some legislation somewhere about the weight of chain Australian men are allowed to retreive as everyone seems to use an electric windlass (and pay a gym membership. :)

Somewhere in the middle of all this development of 'the rode' everyone forgot the benefits of nylon and snubbers are are those who do not respond to

"G'day mate"

Take care, stay safe

Jonathan

I have a correspondent who has access to the soft ware and has a deep understanding of seabed shear stress variations etcand he actually calculated some shackles angles on some American leisure anchor tests (he worked in R&D for the US Navy on anchors and anchoring). Bruce, the oil rig anchor company, market devices called 'Boosters' to suppress the buried chain catenary as a means of beneficially managing shackle angle. I spent some time setting anchors in shallow water off our cat, waiting for the tide to recede, carefully digging the rode out, or at least exposing it and the measuring the angles - it is a real effect - sufficient to negate the paranoia of the 0 degree belief.
 
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Neeves said:
Just note that the scope might actually be 6:1, might not encompass high tide. The cat, which might be a charter boat, might have been equipped with an inadequate anchor, say a copy Bugel. We simply do not have enough information to damn the skipper.

Tell us what the forecast was, what the anchor was, what that 3.5m depth actually means and then we can be harsh or wonder why the skipper had not deployed more rode.

Where we sail we would try to anchor in deeper water as at a depth of 3.5m it would mean being close to shore, close to shore means at low tide the chop/waves stand up and its uncomfortable. We would aim for 5m at low tide, our tides (round Sydney) are a max of 2m (and 10m further north) which converts the water depth from 3.5m to 5.5m add the distance from sea level to bow roller of 1.5m and you have a scope - with 30m deployed of 4:1 - and you wish to damn the skipper....


Jonathan
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Private (English) boat, not Lagoon type so more steamlined. In bay well sheltered from wind and swell. Navily currently giving it 100% protection rating. No tide. Most boats anchored in 3 to 4.5m - he is probably in 3m. Not an anchorage with problems I suggest.

I would prefer a shorter scope but you have to consider what is around you. I have just moved this morning and am down to 4:1 my usual.
 
geem said:
I find it incredible that with weight of evidence from numerous independent tests of various new generation anchors that you cannot accept that they are far better than old generation anchors. New gen anchors generally need less scope. Not the conclusion you come to.
They set far better and hold more reliably. This is not controversial. It's known fact based in weight of evidence. Based in my own experience gained over many years where I previously owned Bruce and CQR anchors, there is no comparison with my Spade anchor. The Spade is fantastically reliable. Something I never experienced with a CQR or Bruce anchor.
Take off the blinkers see the light
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Use whatever anchor you prefer. I am not making any recommendations. I do find it interesting that while historically a scope of 3:1 was the accepted norm with the older style of anchor, it now seems that 4:1 is more common.
 
NormanS said:
Use whatever anchor you prefer. I am not making any recommendations. I do find it interesting that while historically a scope of 3:1 was the accepted norm with the older style of anchor, it now seems that 4:1 is more common.
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Windlasses mean you never have to bother about what goes out, perhaps?
 
NormanS said:
Use whatever anchor you prefer. I am not making any recommendations. I do find it interesting that while historically a scope of 3:1 was the accepted norm with the older style of anchor, it now seems that 4:1 is more common.
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When I had a CQR or a Bruce I needed far more chain than I use now. How many places in the world have you tested your anchor? It might work in your home cruising ground but does it work elsewhere. I have no idea where you cruise but I have noticed how bottom conditions can vary dramatically once you are away from the UK. If I could only choose one anchor it for all bottom types it would be a NG anchor without doubt
 
dgadee said:
What's the thinking on this? Cat near me told me he had 30m of chain out in 3.5m. Is 8 times ok? Selfish?

Or is scope old hat? This article seems to suggest so - How much anchor chain? - Yachting Monthly

This is reasonably quiet time in south of Greece. I wonder what the August sailors would think of large anchoring swinging circles.
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I've always used 12x the square root of the depth. I'm not sure if it is based on any science but it impresses the crew!
 
geem said:
When I had a CQR or a Bruce I needed far more chain than I use now. How many places in the world have you tested your anchor? It might work in your home cruising ground but does it work elsewhere. I have no idea where you cruise but I have noticed how bottom conditions can vary dramatically once you are away from the UK. If I could only choose one anchor it for all bottom types it would be a NG anchor without doubt
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Fortunately, I don't have to choose one anchor. I carry three different designs of bower anchors. They all have their uses depending on varying conditions.
 
AFA I'm concerned bringing freeboard into the calculation is not relevant.
I calculate how much chain to deploy based on the depth of water at HW and the conditions, so if the calculation turns out to be 25m then I stop deploying chain when my 25m marker arrives at the surface of the water, not when it appears on deck or at the bow roller.
 
It is surprising that with the availability of modern anchors and better techniques (such as the more widespread use of elastic snubbers) the trend seems to be towards using greater scopes.

Finding boats anchored overnight at scopes such as 3:1 or 4:1 is becoming less common in my experience.

There is nothing wrong with using longer scopes when this is practical and does not inconvenience anyone else, but I wonder
if modern sailors are more conservative, or is there something else driving this trend? Is the modern tendency towards thinner chain a factor?
 
noelex said:
It is surprising that with the availability of modern anchors and better techniques (such as the more widespread use of elastic snubbers) the trend seems to be towards using greater scopes.

Finding boats anchored overnight at scopes such as 3:1 or 4:1 is becoming less common in my experience.
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I wonder if it's the increase in marina based boats. Anchoring is no longer the norm for most cruisers. In the Caribbean you would think that half the people anchoring have never done it before. Thank God for modern anchors. I think they cover the shortfall in crap anchoring techniques for many sailors. Without them, most yachts would have dragged miles?
 
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