Anchoring with 4:1 Scope?

[Lepke]

Taught in professional marine schools I went to: all chain 4:1, cable 7:1.
The point of enough scope is to keep the anchor's shank from lifting in wave action. In bad weather and heavy currents, I use more than 4:1 even with all chain.

[chris mac]

I'm sure with a new gen anchor, 4to1 scope would be good enough.
For myself however, I've never been satisfied with "good enough" when it's so easy to do "better" or even "great". I sleep much better with 7to1
I understand crowded anchorages and tight anchorages. They are sometimes a necessity. But rarely as a cruiser are they the norm. In my experience they occur in tourist stops or resupply locations. Locations I try to limit my time at.
But, to each their own.

[CarlF]

But if you are using a new age anchor does anchoring with 7:1 scope hold any better than 4:1? (the old "sleep better" test which I've been known to repeat). It still seems to be gospel that letting out more scope will help you hold better - despite no anchor test that I know of showing that.

Looking at the Steve's videos the best anchors at 4:1 scope are burying themselves completely with no indication that a lower lead angle from 7:1 scope would make them bury any deeper or faster. They look headed for China.

And I'm not sure I believe that a few degrees difference in pull vector from a chain catenary is going to make them bury any differently either. It would be an interesting thing to test.

I do agree that chain catenary helps to absorb some shock loading. But my 30ft nylon snubber is a much better way to provide shock absorption. I would never rely just on chain catenary for this.

[Panope]

Originally Posted by CarlF

But if you are using a new age anchor does anchoring with 7:1 scope hold any better than 4:1? (the old "sleep better" test which I've been known to repeat). It still seems to be gospel that letting out more scope will help you hold better - despite no anchor test that I know of showing that.

Looking at the Steve's videos the best anchors at 4:1 scope are burying themselves completely with no indication that a lower lead angle from 7:1 scope would make them bury any deeper or faster. They look headed for China.

And I'm not sure I believe that a few degrees difference in pull vector from a chain catenary is going to make them bury any differently either. It would be an interesting thing to test.

I do agree that chain catenary helps to absorb some shock loading. But my 30ft nylon snubber is a much better way to provide shock absorption. I would never rely just on chain catenary for this.

Carl,

Any anchor will have higher holding power at 7 to 1 scope than 4 to 1.

An exception would occur when the holding is so poor, that catenary cannot be removed at the lower scope. In that case, the anchor will "see" the same angle of pull (0 degrees) regardless of additional scope.

Steve

[hpeer]

Originally Posted by chris mac

I'm sure with a new gen anchor, 4to1 scope would be good enough.
For myself however, I've never been satisfied with "good enough" when it's so easy to do "better" or even "great". I sleep much better with 7to1
I understand crowded anchorages and tight anchorages. They are sometimes a necessity. But rarely as a cruiser are they the norm. In my experience they occur in tourist stops or resupply locations. Locations I try to limit my time at.
But, to each their own.

Quick story.

We go into Dehies, in Guadeloupe. It is a sort of narrow bay, open to the Caribbean, moderate sloping sides and the central bit is quite deep with some soft mud. Because of the mountains the wind frequently shifts and can swing you right around and be real gusty. And it is real popular, its best to go in early in the day to find anchorage room. I have had a guy hit is while trying to anchor.

So we go in, grumble, grumble; the best I can do is a bit deep and in the mud. We drop our 125# Mantus and set it. We go clear in and are grabbing lunch, Im watching the boat. 180° wind shift (or more) and I get a bit nervous so I head out solo to check.

By the time I get to the boat we are a whisker from kissing another boat. I motor up and retrieve the anchor. The anchor is fouled in the chain. It cleared itself as it came out of the water but I could clearly see it fouled.

What I THINK happened is that in the weird 180° shift the slack chain drug back over the shank and fouled it. This occurred because the boat drifted directly back over the anchor.

The other possibility is we fouled the anchor when we set it, but I had backed down hard and she held solid. About 4:1 scope. Now its possible it set into some rock and dropped out when she swung but thats kind of far fetched.

Would more scope have helped? I do not think so, thats just more chain to wrap around the anchor. Less chain? Maybe, but there are other considerations.

Dehais is a funny place and can be a bit challenging in many ways. It seems we never go there with out obtaining a new story. I thought this one might be interesting concerning scope issues even if it is an odd situation.

[markpierce]

Important factor: the quality of the bottom surface to hold an anchor. Thick, heavy mud, as contained in most of the San Francisco estuary, is ideal.

[Panope]

Originally Posted by CarlF

.......And I'm not sure I believe that a few degrees difference in pull vector from a chain catenary is going to make them bury any differently either. It would be an interesting thing to test.......

More shallow pull vector absolutely makes anchors bury better.

Here is the test:

https://youtu.be/i146P6BL7y4

[Mike OReilly]

Originally Posted by Panope

Carl,

Any anchor will have higher holding power at 7 to 1 scope than 4 to 1.

An exception would occur when the holding is so poor, that catenary cannot be removed at the lower scope. In that case, the anchor will "see" the same angle of pull (0 degrees) regardless of additional scope.

Steve

Puts it perfectly.

[thinwater]

Originally Posted by CarlF

But if you are using a new age anchor does anchoring with 7:1 scope hold any better than 4:1? ....

You didn't read the whole thread? You didn't read Noelx's post? The data you are looking for (a few degrees) has been collected. Google holding vs. scope, look for data, and you will see similar data many places. Some brands are better at short scope than others, but the trend is universal.


There is no difference until you anchor in enough wind to straighten the chain substantially, which depends on the depth. There is also no difference if the anchor holds well enough not to drag (hold could be less but you would not notice). Case in point is a concrete block mooring; short scope reduces hold, but the block is very heavy.

People get away with inefficient practices with conservatively sized NG anchors. That's a good thing. It allows them to anchor short, for example. Nothing wrong with that. Hopefully, they realize their practice is sub-optimum before a real storm comes.

BTW, the "sleep well" test is psychology, not engineering, and is thus off topic.

[sstuller]

Try the square rigger anchor test. Sail down wind into an anchorage at three or four knots dropping your hook. If the anchor sets before you hit the beach it is big enough. How's your confidence level?

[Chotu]

Starting to see why I’ve never once dragged in my life when so many others have.

Here I am getting a lousy night’s sleep if I’m down to 6:1 in an extremely tight anchorage while everyone else is trying to see how 4:1 is working out.

I can also see why everyone else uses their engine to pull on the anchor to try to set it. I literally throw mine overboard and dump out 10:1, or at worst case, 8:1. Nature does the rest. Never dragged once in my life and I’ve lived at anchor more nights than on land in my life.

I strongly prefer not to push the envelope in sailing. No navigation shortcuts, no seeing how little scope I can get away with, no leaving port with 5 gallons of fuel and empty water tanks. It’s all the same thing.

If you can take away the uncertainty in boating, why wouldn’t you do that?

[Chotu]

Originally Posted by sstuller

Try the square rigger anchor test. Sail down wind into an anchorage at three or four knots dropping your hook. If the anchor sets before you hit the beach it is big enough. How's your confidence level?

At 3-4 knots, how’s your bowsprit and anchor roller?? Lol

[Dockhead]

Originally Posted by Mike OReilly

Thanks Thin/noelex. My view is that anchoring is such a dynamic event, with many variables both known and unknown, that it just makes sense to be as conservative as one reasonably can. Setting as long as rode as is reasonably possible is part of my this approach.

Well, but there is no sense in just more more more for its own sake. To get a rational answer to this you need to consider other factors -- quality of your anchor, size of your anchor, bottom condition, depth of the water, weather.

If you are in a wide empty place with no other boats around, then sure, just dump out all your chain. But usually there is some other constraining factor, especially swing room.

Fetishizing scope as some people do is harmful, as it will lead them to ignoring other factors, like depth of the water, for example seeking out shallow water in order to increase scope for a given amount of chain .

My anchor is big and good enough (100 pound Spade) that I know that in a reasonable bottom and reasonably deep (10+m) water, 3:1 will hold me in any storm I've ever anchored in. If I'm not constrained by swing room, I will normally put out 5:1 or 6:1, in bad weather more. In iffy holding or shallow water more. I have heavy 1/2" chain, so more of that out gives more catenary, which gives a smoother ride. If I have at least 50m of chain out I normally don't need a snubber. But I know that I can shorten up to 3:1 if I need to and sleep soundly.

I've been through a storm on 2:1 once, when I had no choice (50m of water depth). Set the anchor carefully and didn't budge. There are almost no circumstances where 10:1 makes any sense. As Dashew has reminded us, the more chain you have out, the greater area of the bottom you are sweeping as you swing, and the greater risking of fouling the chain. He has a grossly oversized anchor and has written that he TYPICALLY anchors at 2.5:1.

[Dockhead]

Originally Posted by Chotu

Starting to see why I’ve never once dragged in my life when so many others have.

Here I am getting a lousy night’s sleep if I’m down to 6:1 in an extremely tight anchorage while everyone else is trying to see how 4:1 is working out.

I can also see why everyone else uses their engine to pull on the anchor to try to set it. I literally throw mine overboard and dump out 10:1, or at worst case, 8:1. Nature does the rest. Never dragged once in my life and I’ve lived at anchor more nights than on land in my life.

I strongly prefer not to push the envelope in sailing. No navigation shortcuts, no seeing how little scope I can get away with, no leaving port with 5 gallons of fuel and empty water tanks. It’s all the same thing.

If you can take away the uncertainty in boating, why wouldn’t you do that?

With respect, it's poor anchoring technique to just throw your anchor out and let "nature do the rest". Anchors need to be set. And if you don't bother to set your anchor, you don't even know if the bottom can be anchored in, or not, or whether your anchor is fouled on something. A whole lot of overkill with scope might sometimes make up for failing to set your anchor, but I'd say you've been extremely lucky if you never dragged anchor. I'd much rather lie to a properly set anchor on 4:1, than an anchor just lying on the bottom at 10:1. There is a lot more to know about anchoring than just letting out a bunch of scope, and it's a lot more work than just dumping out all your chain, to do it properly.

[SV Siren]

Not to throw a wrench into the conversation, but here goes anyways

My boat when I purchased her, came with a rather large kellet. Does anyone use these much anymore, and should I keep it. I have rather oversize ground tackle now on all chain..