anchor scope

[Kettlewell]

I find it odd that Casey chose 4:1, as that is perfectly in-between what many experienced cruisers consider a minimum scope of 3:1 and a normal scope of 5:1. In any case, Robert Smith actually did a lot of load testing on anchors and wrote about it, and he said that on average there was an increase in holding of 43% when the scope was increased from 3:1 to 5:1. That isn't insignificant, but it doesn't answer the question if most of this increase is achieved by 4:1.

I frequently anchor in less than 10 feet of water here on the East Coast, and 5:1 means I only have to put out (10 + 5) x 5 = 75 feet of rode, so the swinging circle isn't excessive. If winds are light I can shorten up to 4:1, which does seem to work in the typically less than 25 knots of wind we see in the summer on the East Coast. So if the answer is that you can anchor with 4:1 in normal conditions I think he is correct, but I do also think that increasing scope increases holding power significantly beyond that point.

There is also the important point that longer scope means more catenary and/or more bounce in the nylon, which reduces loads on the anchor. So you get a win-win situation: greater holding power and less peak loads to deal with.

[Kenomac]

There's no special formula for scope that works the same for everyone or for every location. I'm certainly no expert world cruiser, but I look at every anchorage for what it is, bottom, wind, waves, tide, other vessels etc., then I put down the appropriate anchor and scope for the conditions.

Forget the published recommendations, our priority is to sleep well and to not ever have to explain to our insurance company, why the boat dragged anchor and ended up on the rocks while we were all ashore.

If it's crowded, I try to anchor a little further out to avoid the crowd, which I can do with 100 meters of chain in the locker. If I'm the first one there and I'm going ashore, I send at least 60 meters of chain over the side in 25 ft of agua and let the others worry about staying out of the way. I've placed a 60 meter mark on the chain.

[sailorboy1]

doesn't seem that the group supports the 4:1 (normal in the article was up to 40 knots wind)

[boatman61]

Originally Posted by Don L

Also related to the BIB thread he says: "You can also try switching to "better" anchor if you like, but when you do so double down on your bet and make it bigger as well."

I do so love an 'Expert'...

[zeehag]

Originally Posted by Don L

doesn't seem that the group supports the 4:1 (normal in the article was up to 40 knots wind)

having watched as boats drag anchor and seeing what kinds o fanchors and chain and techniques folks use has been a kind of hobby for me since 1990 as i do not keep a tv on board. is quite entertaining as well as informational.
4:1 is not sufficient in west coast usa or mexico, as swells and winds WILL cause a dragging incident. go figger. with swells to 5 meters, you will not fare well with only 4:1 scope. especially in windy situations..yes we have biiig winds on west coast. funny thing about that. rocky bottoms also...funny thing about that.
i just re anchored into 14 ft water at high tide--with 100 ft chain. i should be ok into a tormenta(fancy spanish word for electrical storm to make florida jealous), at which time i will either be somewhere else with boat or i will let out more chain. i vote for elsewhere. is time to move south more, as soon as work is finished so i can leave under power or sail...i like options.

[Hudson Force]

Someplace, a few pages back, it was said that increasing the rode length doesn't lessen the load on the anchor, but just makes it more hoirzontal. I would say that this is generally true and yet still benefits holding; however, I recall an exception. I anchored for two hurricanes in a shallow cove with a six foot depth and soft mud. I was pretty much alone in this space and put out 250' of chain. With the height to my bow roller this would be a seemingly ridiculous 24:1 scope, but a great length of my chain was well beneath the mud during the strong winds and I'm confident that this did lessen the load on my anchor.

[Tomm0]

If the chain out is so heavy and has so much bottom friction that its almost a mooring block, of course it will reduce demand on the anchor. 250ft could do that... In light weather you could probably use it without an anchor!

[thinwater]

Don Casey is published is Sail and is therefore a god (small g). Real testing? Rubbish. Just kneel down.

He presents one experience as though it were universal. It is not. He presents a specific anchoring situation--deep water over good holding in crowded conditions--which is not normal at all on the east coast. He presents numbers with without providing any basis for the calculations (simple trig I'm guessing, that disregards the effects of surge, catenary, and sailing at anchor--done that way I can recreate his figures).

He is correct in that more rode doesn't always help holding power. More rode can increase sailing surging. Of course, his less rode pitch neglects the vertical motion and devastating effect that can have in a shallow anchorage on all chain, when the chain snaps tight against a swell. Ouch.

He does allow that you should set the anchor first at 7:1, but in a soft mud anchorage--common on the Chesapeake--it is often sensible to let the anchor settle in first, unless you like plowing groves. Could I set it an hour later and then shorten up? I probably won't.

As I said, rules for one specific sort of anchorage, a kind Chesapeake sailors seldom see.

But he is a god.

---

Yes, I have used a variety of anchors (Fortress/Northill/Delta/Mason Supreme) and both mixed and all-chain rodes. I like the new anchors, but they don't suspend physics or change fluid mechanics.

I actually thought it was a reasonable article written for beginners that don't know squat. That seems to be the target audience of the new Sail Magazine. There is really very meat for the more experienced sailor, but they practically gave subscriptions away a few years ago. No reason to renew.

[sailorboy1]

Originally Posted by thinwater

There is really very meat for the more experienced sailor, but they practically gave subscriptions away a few years ago. No reason to renew.

$7/yr and the issue I used on this thread is a free one I picked up when I signed up. For $0.60/issue I thought it was worth some bathroom reading, but I wonder?

[zeehag]

with a lot of chain on a semi rock bottom, the chain can wrap on rocks and make life a lot noisier and much safer as you will not drag. short scope--impossible to wrap a rock, can drag.
anchoring in a wrecked boat is good--you will not drag..do not use rope rode, as it will chafe and you will walkabout. could be difficult to extract from wreck-may need diver.

best way to learn what works is to practice practice practice. is funner, also.

[Kettlewell]

In my many years of observing with keen interest how people are anchoring around me I see the #1 problem being the use of too short a scope. I think it starts with many boaters having no idea how much chain or line they have out because it isn't marked. Many don't add in the height of the bow when figuring scope. Often they forget to compensate for the state of the tide. So what happens is you get someone who comes in and anchors in 10 feet of water, so they let out maybe 50 feet of chain thinking they are now using the recommended 5:1 scope. But, the bow roller is 6 feet off the water, and it is low tide so you have to add another 4 feet for that, so in reality at high tide they are on a scope of 2.5:1 at 2am when the thundersquall comes through with a violent wind shift.

[denverd0n]

Originally Posted by thinwater

Don Casey is published is Sail and is therefore a god (small g). Real testing? Rubbish. Just kneel down.

Did you even read the article? I'm guessing not.

Don Casey is a very experienced cruiser, an intelligent and educated man, and generally comes across as quite humble. You may mock him as a "god," but I am quite certain that he has no illusions about his human shortcomings. He is always very clear about what "real testing" he, or others, have done and about what is just his opinion, based on his experience.

As to the original question, I suspect that a lot of us are uncomfortable with scopes of less than 5:1 simply because that was what we always heard when we were learning. From the empirical evidence out there, I'm not sure I'd agree that there is no material benefit over 4:1, but it is pretty clear that the returns begin to diminish dramatically beyond that point.

[denverd0n]

Originally Posted by Kettlewell

So what happens is you get someone who comes in and anchors in 10 feet of water, so they let out maybe 50 feet of chain... But, the bow roller is 6 feet off the water, and it is low tide... so in reality at high tide they are on a scope of 2.5:1 at 2am when the thundersquall comes through with a violent wind shift.

Exactly. And those are the ones who are at least trying. I can't even count how many times I've seen someone come into an anchorage, drop the anchor until the rode goes a bit slack, and then snub it off there--essentially a 1:1 scope! Do they even realize that, when the tide comes in, their anchor is going to be off the bottom completely? Probably not.

[thinwater]

Originally Posted by denverd0n

Did you even read the article? I'm guessing not.

Don Casey is a very experienced cruiser, an intelligent and educated man, and generally comes across as quite humble. You may mock him as a "god," but I am quite certain that he has no illusions about his human shortcomings. He is always very clear about what "real testing" he, or others, have done and about what is just his opinion, based on his experience.

As to the original question, I suspect that a lot of us are uncomfortable with scopes of less than 5:1 simply because that was what we always heard when we were learning. From the empirical evidence out there, I'm not sure I'd agree that there is no material benefit over 4:1, but it is pretty clear that the returns begin to diminish dramatically beyond that point.

Please. That's the kettle calling the kettle black, since perhaps you didn't read the balance of my post. And I was just having a bit of fun. The mocking was a critisism of the flock--accepting the written word as gospel--not of the man; I'm sure he expected challenges and wouldn't mind. Perhaps I should have been more clear.

1. I mentioned that his figures were the result of simple trig. I repeated them. I think the calculations oversimplify the situation.
2. I mentioned I subscribe to the mag. Figures I read it.
3. I'm right about the variable harbor situation. He is experienced in some areas, but not everywhere and one size does not fit all. But after all, it was just a mag article and thus beginner stuff.

An I know a number of places that getting any anchor to set at 4:1 is a fool's errand. Sand, sure, soft silt or hard clay, nope.

I've spent 30 years as an engineer and 25 years as a sailor. I've learned anchoring defies simple engineering evaluation, for the reasons he gave and some more he skipped.

[Cheechako]

Originally Posted by Don L

I read something in Sail the other day that caught me off guard. It was in the letters to the experts (and I think Don Casey gave the answer) and was about anchoring.

The thing that caught me was that he said there is no data that scope of more than 4:1 was of any use. Now I learned the standard 7:1 rule and accept that "all chain" of 4:1 when things are normal is enough. But in this case he is saying that 4:1 is as good as it gets and than more than that doesn't ready change the angle far as the anchor shank etc. and doesn't really help.

Once I started thinking about it I could not really think of any real studies or tests with higher scope and had just accepted the "more is better" thinking. Anyone have any links to something about scope far as tests?

Yeah, I read that article too, it was in this months sail mag. Kinda caught me off guard... a tow truck with some anchors on a beach might solve that question.... More scope (with all chain) means more weight on the ground so I suppose that is a small added benefit. But it is a good question, at what point does the decrease in angle stop making a difference? I bet it's specific to anchor design....