Anchoring with 4:1 Scope?

[Mike OReilly]

Originally Posted by SV__Grace

Mike, Yep, it's the time you don't deploy your safety device that you end up needing it!

You've probably seen my previous posts on my "Hidden Trip Line" strategy and this discussion of trip lines reinforces the benefits for me. Easy to deploy, unobtrusive, won't be tripped by another boat, and in the past two years of deploying it 100% of the time (which is a lot, we live on the hook) I've never had a problem or had to use it! (knock on wood).

Thanks Grace. I like's it! Seems simple enough to deploy as needed, and it sounds like it would be no more of a challenge than dealing with the float and line.


I'll definitely rig this the next time I see my boat (whenever that might be ).

[thinwater]

Originally Posted by Dockhead

It's not that clear. Laying crab pots in a legal area is clearly legal. But laying a crab pot in a marked channel (say) is not, and if you cause damage to someone you will pay. The case of anchor floats is not clear one way or the other. Such a case would be decided based on the preponderance of the evidence -- expert witness vs expert witness on the question of whether it's good seamanship or not. And I think it's not unlikely that a judge might be persuaded that it's not (since it is ISN'T good seamanship).

Yes, and if I were your lawyer, that is exactly what I would argue. But whether that is persuasive or not is another question. I would prefer to be arguing the other side where I think the case is much easier to make.

And if for some reason I really wanted to use an anchor float in a crowded anchorage despite the large weight of qualified opinion that it is unseamanlike, and discourteous -- I would be seriously concerned about liability. It is a seriously bad practice.

I dig your enthusiasm and I don't like floats, but as a judge you would have to convince it was clearly negligent, and as we can see, there are too many that like the practice. All I have to argue is that we disagree.


---


I also find it pretty funny when people attach the float to the wrong eye. This is the lashing eye, not the tripping eye. That won't free it from a good snag, because it pulls up not back. at what angle does you anchor hang like that? Just sayin'.

[Dockhead]

Originally Posted by thinwater

I dig your enthusiasm and I don't like floats, but as a judge you would have to convince it was clearly negligent, and as we can see, there are too many that like the practice. All I have to argue is that we disagree. . . .

It's a legal question. How widespread the practice is, may be evidence of the "ordinary practice of seamen", which might help the defense of such a case if it could be established that the practice really is widespread, but that is only one aspect of the question. There is no such legal concept as "clearly negligent" -- you're either negligent or not, and in civil cases, negligence is proven by a "preponderance of the evidence", famously defined as "one iota" more evidence that it was so, than that it was not, a a pretty low bar, a much lower bar than "clear and convincing proof" or "proof beyond a reasonable doubt", standards of proof which are applicable in other types of cases. And negligence itself is not the only possible basis for liability here. You can believe me or not, but there is significant exposure for liability here. It doesn't mean that you would for sure lose, but don't be suprised if you get sued, should a vessel come to grief by getting tangled in your anchor float deployed in a crowded anchorage, and don't be suprised in such a case if your lawyer advises you to settle because he can't guaranty that you will win. It's a serious issue.

[Idlegreg]

Originally Posted by wernerP

Here is my approach so chain length: I don`t think that the anchor is caring at all how much chain is going up to the boat. The anchor cares only about the horizontal force that pulls on him. If I feel happy with having 20 m/60 ft of chain on the ground plus 5 m of rounding to the vertical part - always, no matter what depth - I need only to add the water depth + the hight of my hull. It will show that more depth doesn`t require sooo much more chain.

Maybe I don't understand but I wonder - what keeps the 20m of chain 'on the ground' ?


I mean when the wind blows or some waves lift the bow doesn't all the chain stretch tight between bow roller and anchor ?


It is likley your method will work in many common anchoring depths and even in deeper water, if conditions are gentle, but are you saying that in 20m of water/bow height you would only put out 45m of rode ?

That seems dangerously marginal to me - and I have spent 40 years anchoring with far too little scope - accoring to many of the posters on here - and almost never with a snubber ! (Ducks and hides :-)

[thinwater]

Originally Posted by Dockhead

It's a legal question. How widespread the practice is, may be evidence of the "ordinary practice of seamen", which might help the defense of such a case if it could be established that the practice really is widespread, but that is only one aspect of the question. There is no such legal concept as "clearly negligent" -- you're either negligent or not, and in civil cases, negligence is proven by a "preponderance of the evidence", famously defined as "one iota" more evidence that it was so, than that it was not, a a pretty low bar, a much lower bar than "clear and convincing proof" or "proof beyond a reasonable doubt", standards of proof which are applicable in other types of cases. And negligence itself is not the only possible basis for liability here. You can believe me or not, but there is significant exposure for liability here. It doesn't mean that you would for sure lose, but don't be suprised if you get sued, should a vessel come to grief by getting tangled in your anchor float deployed in a crowded anchorage, and don't be suprised in such a case if your lawyer advises you to settle because he can't guaranty that you will win. It's a serious issue.

Yeah, the bit about settling is certain!


Well, it won't be me with the float.

[Dockhead]

Originally Posted by Idlegreg

Maybe I don't understand but I wonder - what keeps the 20m of chain 'on the ground' ?

I mean when the wind blows or some waves lift the bow doesn't all the chain stretch tight between bow roller and anchor ?

It is likley your method will work in many common anchoring depths and even in deeper water, if conditions are gentle, but are you saying that in 20m of water/bow height you would only put out 45m of rode ?

That seems dangerously marginal to me - and I have spent 40 years anchoring with far too little scope - accoring to many of the posters on here - and almost never with a snubber ! (Ducks and hides :-)

I think there's actually a grain of truth to what he says. I wouldn't take it literally, for the reason you correctly stated.


But it is true that the same scope represents different amounts of chain in different depths, and that this behaves differently. It's the primary reason why a scope which seems too short in shallow water, might work splendidly in deep water. Especially if you have heavy chain.


When I have all 100 meters of my 1/2" chain out -- so 330kg of it or nearly half a short ton -- 3:1 is very secure. 30 meters of water is NO problem. And forget the snubber -- calculations show that it is almost impossible to pull all the catenary out of it in water that deep. But in 3 meters of water? That's only 10 meters of chain -- whole different story.


Depth is really important -- you can't just mindless apply the same standards of scope, across all depths.

[Idlegreg]

Originally Posted by Dockhead

I think there's actually a grain of truth to what he says. I wouldn't take it literally, for the reason you correctly stated.
.......
Depth is really important -- you can't just mindless apply the same standards of scope, across all depths.

DH - I agree with all of that.



But the specific numbers given in the example I quoted are unlikley to be OK in all circumstances so I could not resist commenting, especially as the real danger is a fixed rule, without taking into account the particular situation. I saw the link someone posted to an apparently mathmatical assesment suggested 15m plus 2x depth, or something like that, and I absolutley agree that makes more sense than a fixed multiple of depth, at least if anchoring with chain.



Although I would say, if asked, that I anchor on 3:1 (I read it in a book many years ago) that is not really true, as instead of stopping at the precise length I operate on the 'plus a bit' principle and like many have said it all depends on so many factors, many of which would lead me to add more scope. I rather like anchoring in tight spots with limited room but decent shelter and good sticky Mud. I also take the view that the consequence of dragging is relevent (though I cannot remember the last time I did drag into danger). Alone, way up a muddy creek, then the worst likley outcome is I get to spend some time on the Mud. Except it does not happen, because anchoring with all chain and no snubber I am woken up if the conditions deterioate.


This of course does not apply if I am going ashore for any length of time when the weather could change or the tide could turn while I'm ashore. Then as in many other situations I might be more conservative.


Another thing I read many years ago was an account of Adlard Coles anchoring in a gale in the Frisian Islands, where he concluded a long stretchy warp is better than chain in bad weather and very shallow depths. I try to keep that in mind, though rarely have to use the method.


The truth is that even before the internet, for most of my sailing, I have had the luxury of multiple shipping forecasts per day and I had an engine (plus was lucky enough to sail in an area with few Thunderstorms). So much of my sailing life has been spent choosing anchorages that are well suited to the weather I encountered. I realise that for others there is good reason for more scope and don't deny it can significantly increase holding but I do think people should accept that with a reasonable weight of anchor and chain, and good weather, you will often be safe on 3:1. (I just looked and it seems the current RYA advice is 4:1 chain & 6:1 for rope/chain, which seems sensible)

I don't think shorter scope is relevant if you are living on the hook but can be OK on many occasions if you are moving on each night.

[Dockhead]

Originally Posted by Idlegreg

DH - I agree with all of that.

But the specific numbers given in the example I quoted are unlikley to be OK in all circumstances so I could not resist commenting, especially as the real danger is a fixed rule, without taking into account the particular situation. I saw the link someone posted to an apparently mathmatical assesment suggested 15m plus 2x depth, or something like that, and I absolutley agree that makes more sense than a fixed multiple of depth, at least if anchoring with chain.

Although I would say, if asked, that I anchor on 3:1 (I read it in a book many years ago) that is not really true, as instead of stopping at the precise length I operate on the 'plus a bit' principle and like many have said it all depends on so many factors, many of which would lead me to add more scope. I rather like anchoring in tight spots with limited room but decent shelter and good sticky Mud. I also take the view that the consequence of dragging is relevent (though I cannot remember the last time I did drag into danger). Alone, way up a muddy creek, then the worst likley outcome is I get to spend some time on the Mud. Except it does not happen, because anchoring with all chain and no snubber I am woken up if the conditions deterioate.

This of course does not apply if I am going ashore for any length of time when the weather could change or the tide could turn while I'm ashore. Then as in many other situations I might be more conservative.

Another thing I read many years ago was an account of Adlard Coles anchoring in a gale in the Frisian Islands, where he concluded a long stretchy warp is better than chain in bad weather and very shallow depths. I try to keep that in mind, though rarely have to use the method.

The truth is that even before the internet, for most of my sailing, I have had the luxury of multiple shipping forecasts per day and I had an engine (plus was lucky enough to sail in an area with few Thunderstorms). So much of my sailing life has been spent choosing anchorages that are well suited to the weather I encountered. I realise that for others there is good reason for more scope and don't deny it can significantly increase holding but I do think people should accept that with a reasonable weight of anchor and chain, and good weather, you will often be safe on 3:1. (I just looked and it seems the current RYA advice is 4:1 chain & 6:1 for rope/chain, which seems sensible)

I don't think shorter scope is relevant if you are living on the hook but can be OK on many occasions if you are moving on each night.

Well, if there is room to swing, 6:1 or 8:1 is great. Even in deep water. But otherwise, 4:1 is perfectly adequate in reasonably deep water (say, at least 10m). If you have a reasonably oversized anchor, and the bottom is reasonable.

Shallow water (less than say 5m) is a special challenge. I actually avoid it when I can. Here you certainly want more scope. And a long stretchy snubber.

[Idlegreg]

Originally Posted by Dockhead

Well, if there is room to swing, 6:1 or 8:1 is great. Even in deep water. But otherwise, 4:1 is perfectly adequate in reasonably deep water (say, at least 10m). If you have a reasonably oversized anchor, and the bottom is reasonable.

Shallow water (less than say 5m) is a special challenge. I actually avoid it when I can. Here you certainly want more scope. And a long stretchy snubber.

Hmm - well I'll try not to feel bad - I often anchor in shallower water without snubber and pretty short scope, but then it is in smaller baots and I am talking about decent and sheltered anchorages. It is true most of my experience is heavy long keel boats with low freeboard and it may be the case they lie much more quietly in given conditions.


On both my own boats I have been limited in available anchor chain (30m on my 21' boat and 40m on the current 33' boat) so if I want more scope I have to attach a warp, which means I rather like to anchor in reasonably shallow water.

[Icarus]

Originally Posted by CarlF

I've been anchoring for 40 years. First boat had a CQR so I always used 7:1. As I've gone to better anchors I've shortened up a bit and now use 5:1.

But S/V Panope's anchor tests on YouTube are eye opening. His standard test is at 3.5:1 (and a short scope test at 2.5:1). The anchors that do well in his testing all set, hold, and reset repeatedly at this scope. There's no evidence in the video that more scope would make them hold any better.

Going to 4:1 scope will mean I'll have to worry less about swinging in a crowded anchor and will mean that my 150ft of chain (spliced to 150ft of brait) will be 100% chain in even deep anchorages.

I know this will seem like sacrilege to many but there's no magic to 7:1. Or science either. It's just the scope you needed with a 50 year old anchor design like the CQR.

Thoughts?

Here's S/V Panope's test of the Excel which I think will be my next anchor.

I had a 25kg plough on my 40 ketch, usually i let out 4:1 plus, dragged once in 35kn gust, only once I let out about 7:1 in a blow on a lee shore and a 2m swell
Now i have a Sarca Excel #5, still let out 4:1
I have 80m of 10mm chain and about 30m of nylon.

[moseriw]

I would stay off everything that looks like CQR. Danforth design is the way to go. Or maybe Rocna like designs.

Did you know that the CQR was designed as dragging tackle at river thames?

[MathiasW]

Originally Posted by Don C L

Now that brings up a good point. The slope of the bottom can either really help your holding power or dramatically reduce it. If you are trying to pull an anchor up a slope you can get by with less scope; the anchor will be digging into the slope. But if you are pulling an anchor down a slope you may never have enough scope to make that work. All the discussion so far has assumed a flat bottom. In addition, the material on a slope, whether it is sand, mud or gravel, is going to be far less stable. In my own area I anchor bow and stern in small coves. At times at night the wind will blow off the beach and if I have set my stern anchor in the slope of a sandy beach I cannot count on it. This is especially true if there is any wave action that may loosen the sand.(So I have to make sure I am far enough off the beach to have both anchors in the flatter, more stable, finer grained, bottom.)

Yes, it is indeed true that the pulling angle is better, if I have to pull the anchor upwards, so when the slope between anchor and vessel is positive.

But there is a serious downside to it: Chain works, because it stores energy in form of potential energy. Storing here means to look at the chain's potential energy before the gust blow / swell impact, and thereafter, and to take the difference. The larger the difference is in the shape of the chain between these two points in time, the more potential energy gets stored. So, if you have a positive slope between anchor and vessel, the chain will also be following that slope when "at rest". Then, when the blow comes, it can lift up only very little, since it is half-way there already, anyway.

Just consider the worst case when the slope between anchor and vessel is such that the water depth at your vessel is zero... Well, apart from the slight inconvenience of having run aground , it is obvious that in such a scenario the chain cannot absorb any potential energy at all, and so every additional pull at it will go straight to the anchor load and is not absorbed by the chain at all.

Consequently, with a positive slope the chain will store little energy and the swell / blow will have to be absorbed elsewhere. With a snubber / bridle, or somewhere else in the anchor rig.

I hope my picture is clear enough. What I am saying is that it is generally a bad idea to "take advantage" of a slope when anchoring. Yes, it is good for dealing with static forces, but any dynamic jerking at the vessel and anchor are not absorbed well by a chain when it is lying already "uphill".

The exception would be a positive slope of a few meters and then it is flat again, but that seems like a very constructed special case.

Other than that, for those who are interested in the modelling of anchor chain and have not participated in that thread at the time, here it is:

https://www.cruisersforum.com/forums...pe-235053.html

Be warned - it is a very long thread and meandering a bit, as threads tend to do...

My own summary and conclusions can be found here:

https://trimaran-san.de/die-kettenku...atiker-ankert/

It explains why anchoring at shorter scope in deep water works - simply because the chain is much better then at deploying the catenary effect, and many other stuff as well.

My primary goal of all this was to understand why I am using a certain scope in a certain situation, and when I am getting to the limit, without having to do potentially dangerous experiments with various amounts of chain length.

Old experienced sea bears will not need it, but for folks with less experience it may prove useful.

You will also find pointers there to apps for Apple and Android that I have created meanwhile. (I have decided to charge for them, as the app stores ask for annual fees to keep them alive in the store. Whilst I am happy to spend my time on this matter, I am hesitant to pay annual feels for it year after year.) We (i.e. my son and I) are struggling quite a bit to make a free online web version work. It seems much harder than initially expected, but eventually we will...

And as to 4:1 scope... We are currently anchoring at 8 m plotter reading at low tide, with 3.5 m between my point of reference (bottom of keel) to bow roller. This means a water depth of 11.5 metres minimum, and 16 metres at high tide. As it is a very secluded corner in the bay, I have assumed a maximum speed at anchor of only 0.1 knots to account for swell. Furthermore, assuming a maximum wind of 27 knots (which is not expected even remotely here for the coming week), my calculator arrives at a minimal chain length of 73.5 metres - at low tide. For 12 kn of wind this would go down to 36.5 metres.

All this depends on some vessel characteristics such as chain thickness, windage area, vessel weight, and quality of snubber / bridle. So, it is really impossible to give a rule that fits for all.

Ah, and before I forget. In Germany the official sailing association where you need to take your tests for sailing certificates uses 3:1 scope as the only correct answer in their exams. So, beware of those folks having come fresh from such an exam...

Cheers, Mathias

[MathiasW]

Also, what I find very useful to study is the elasticity of the chain, defined as how much additional potential energy does it store when I increase the pulling force by a tiny little.

Doing this analysis it turns out that a chain is more comfortable in deep water, at a surprisingly small scope. But it has to be in really deep water for this scope to apply.

On the other hand, when in very shallow water, the chain is almost horizontal to begin with between anchor and bow roller, and so it cannot gain much more potential energy anymore. In such a case the chain becomes very poor and needs to be complemented by snubber / bridle for the anchor gear to work.

For this reason I tend to anchor in slightly deeper water and happily leave the beach area for others.

[Don C L]

Originally Posted by Dockhead

It's a legal question. How widespread the practice is, may be evidence of the "ordinary practice of seamen", which might help the defense of such a case if it could be established that the practice really is widespread, but that is only one aspect of the question. There is no such legal concept as "clearly negligent" -- you're either negligent or not, and in civil cases, negligence is proven by a "preponderance of the evidence", famously defined as "one iota" more evidence that it was so, than that it was not, a a pretty low bar, a much lower bar than "clear and convincing proof" or "proof beyond a reasonable doubt", standards of proof which are applicable in other types of cases. And negligence itself is not the only possible basis for liability here. You can believe me or not, but there is significant exposure for liability here. It doesn't mean that you would for sure lose, but don't be suprised if you get sued, should a vessel come to grief by getting tangled in your anchor float deployed in a crowded anchorage, and don't be suprised in such a case if your lawyer advises you to settle because he can't guaranty that you will win. It's a serious issue.

Hmmmm... It may considered in some cases prudent to set trip lines for anchors where retrieval is in question. I would think a judge would have to take many things into consideration. Where I am I have set trip lines on anchors, bow and stern, though very rarely, in places that may have rocky outcrops. And I have sailed into anchorages where others have too. As long as the buoys are bright and visible and their lines are weighted, I have no problem with it. In fact knowing exactly where someone else's anchor is is information I am glad to have! BUT these are anchorages where anchoring bow/stern is the norm so there is no threat from swinging over someone's buoy.

[Dockhead]

Originally Posted by Don C L

Hmmmm... It may considered in some cases prudent to set trip lines for anchors where retrieval is in question. I would think a judge would have to take many things into consideration. Where I am I have set trip lines on anchors, bow and stern, though very rarely, in places that may have rocky outcrops. And I have sailed into anchorages where others have too. As long as the buoys are bright and visible and their lines are weighted, I have no problem with it. In fact knowing exactly where someone else's anchor is is information I am glad to have! BUT these are anchorages where anchoring bow/stern is the norm so there is no threat from swinging over someone's buoy.

Sure. And I've said myself that I have and use an anchor buoy myself in such cases. In very uncrowded places it's not a problem, at least if you have a LIGHT on your buoy (you do, don't you?). But we were talking about CROWDED anchorages. That is a whole different ballgame.



Having thought a lot about SV Grace's ingenious "hidden trip line", it now seems to me, however, that this is an absolutely superior solution to the problem. I will be trying that out, and if it works like it seems to me like it will, I may never use an anchor buoy again.