Anchoring with 4:1 Scope?

[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.

https://www.youtube.com/watch?v=0_NjTRAJ0FU

[tkeithlu]

Long, long, ago in an ocean far, far away (Like 1960 in the Atlantic) the books said 3:1. Across my years in boats the common knowledge scope has stretched to even 7:1. Hell, we only had Dansforth anchors, not plows of any sort.

There is no magic number. It's your judgement call given your boat, the size and type of anchor, the bottom, the rode you use, and the winds and waves. With that many variables no single number could possibly be a "RULE."

However, I did used to know a couple, now quite experienced and wonderful in any case, who in their first boat let out 35' of rode because the water was 35' deep...

[Benz]

It's rare that I let out as much as 5:1; usually 3:1 has been enough with my Manson Supreme. I like a heavier anchor with less scope rather than lighter anchor with more.
I've never heard anyone advocate 7:1 scope before--that just sounds ridiculous.

[sailorboy1]

Well a 4:1 with a new generation anchor is a lot different than 4:1 with a CQR field plow anchor

IMO and experience.

[Cheechako]

I've anchored many times at about 4:1. My normal is 5:1. But if you know the bottom, and/or it is coarse sand, or there is no fetch from any direction for wind waves, ... no problem. It's simple to let more out anyway.

Although I started cruising in the CQR popularity era, I always hated them. Most people don't realize that they almost always lay on their side, due to the huge knuckle weight. Then unless the bottom is perfect, they just drag along on their side.
That's what Delta figured out and changed. My Deltas almost always set upright like they should. Now even better modern anchors rule.

[Don C L]

Under most conditions, especially with oversized anchors and all chain, I suspect Steve would agree 4:1 is fine. I can only reflect on times when I have been anchored not just in strong winds but in a rough anchorage with the bow pitching on a heavy full-keel boat and the rode out on a roller a a foot or so out on the bow sprit. If the chain or nylon line is taught enough that it is starting to lift off the bottom at the anchor then the anchor may start to get pulled at a higher angle to the point where it is not trying to dive down into the bottom anymore. If the fluke angle is lifted and it is no longer trying to dive, then personally I'd be concerned and I'd keep laying out scope until the angle ensures the anchor shank never gets a jolt upward by a pitching bow. Of course, we are never able to watch what is happening down there so Steve's videos are invaluable. One thing you might check also are those videos where anchors do not set well after a reversal. It may not necessarily always be a scope problem in those cases but the more the rode is laying on the bottom while pulling, the better I figure. Draw a diagram with the rode taught at 4:1, with the rode exiting from it's maximum height when pitching and look at the angles. If an anchor can be pulled at that angle and still continue to dive into the bottom, then it should be good to go.

[Mike OReilly]

There is no magic number here. More is always better. Panope's tests say nothing about this. His tests are intended to be extreme anchoring situations, not arguments for a new normal.

In general, the newer anchors set better and have greater ultimate holding power than most of the older designs (Danforth-style still wins, but in a narrow band of substrate). This is why we can get away with shorter scopes most of the time. But that doesn't mean one should deploy less.

It's all about trigonometry and force vectors. The longer the hypotenuse of the anchoring triangle the smaller the ultimate pull angle on the anchor, and the greater the horizontal force vector. All anchors work by digging in, and the greater the horizontal vector, the better they do this.

I believe it was Noelex (another great contributor to anchoring know how) cites research showing that rode ratios beyond 10:1 really make no measurable difference. I have laid to 4:1 or even 3:1 on very rare occassions, but unless I'm constrained by geography or other boats, I never willingly lay out less than 5:1. And if there's space, I happily put out more.

[noelex 77]

An anchor’s holding ability with varying scope is an important question that could do with more research, but there are at least some ball park figures available.

Some anchor manufacturers publish data. These are typical results:

Scope Holding
10:1 100%
7:1 85%
5:1 70%
3:1 40%
2:1 10%

4:1 often produces more than adequate holding ability and is therefore a commonly used anchor scope. This is especially true with the modern trend to use oversized new generation anchors.

There are other very important factors such as the quality of the substrate, slope of the bottom, and depth of water to name but a few that play an important role in selecting an adequate scope.

There are downsides to larger scope such as larger swing circle.

[Tomodore]

Agree that conditions and bottoms rule. This past summer in the Sea of Cortz there was usually a chance of a Chabasco resulting in sudden high winds in mostly empty anchorages. Lots of scope and heavy duty snubber bridle of 30 feet. Now on the Mexican Gold Coast very little likelihood of much wind and many more boats in anchorages. Just a dock line for snubber and short scope. Practical Sailor has some testing on holding power and scope and it surprised me how much 7/1 outperforms 4/1. I do ask my neighbors how much scope if I am close and I love my golf range finder for gauging how far the rocks and other boats are.

[tenchiki]

I used to have a "How To Anchor" pamphlet from Danforth which advocated for rope rodes with a very short bit of chain, saying that 7:1 was the minimum scope for best holding power for a lightweight (ie: danforth/fortress style) anchor. It also advocated for using 2 anchors to limit swing and eliminate resetting, either bow and stern or bahamian style, depending on currents, etc.
This was also back in the times of "what is the lightest anchor you can get away with".
I wonder if I can still find it? I gotta stop being such a packrat...

[thinwater]

You cannot have a discussion of chain rode scope independent of depth. The reason is that the effect of catenary is HIGHLY dependent on how much chain is out. In moderate conditions, the number of feet of chain can be as important as the scope.

One sailor will say 3:1 is enough. Another will say 7:1. The first sailor is probably assuming 20' from roller to bottom (16 feet of water) and BBB chain, and the other might be assuming 6' from roller to bottom (I've done this many times) and G43 chain. In the latter case I would have 18 feet of chain (13 pounds) at 3:1 and I could pull the curve out with one hand without leaning. Heck, my bridle is that long. How ridiculous would it be to anchor with no rode? In the former case he has 60 feet of chain (95 pounds) and it would take a fresh breeze to lift that.

Another factor in very short rodes is that the max amount of stretch (nylon) or chain is very limited. If a wake hits, there is simply too length to provide energy absorption, whether chain or rope.

An additional rule of thumb that I find useful is to deploy no less than 75 feet of chain (50 feet if very shallow). A corollary is that unless the water is very deep, you're seldom going to need more than 200 feet of chain, because that's enough weight for catenary to be effective in breezy conditions.

Play with a catenary calculator and you will see the sense.

Real storms, even squalls change the math a bit. Nuf' said without getting off topic.

Nylon also has a practical limit in terms of stretch. About 30 feet is the minimum for combination rodes, to avoid overload. However, the catenary effect is much less (there is a chain leader--it's not zero) and minimum scope is less dependent on depth.

[thinwater]

Originally Posted by noelex 77

An anchor’s holding ability with varying scope is an important question that could do with more research, but there are at least some ball park figures available.

Some anchor manufacturers publish data. These are typical results:

Scope Holding
10:1 100%
7:1 85%
5:1 70%
3:1 40%
2:1 10%

4:1 often produces more than adequate holding ability and is therefore a commonly used anchor scope. This is especially true with the modern trend to use oversized new generation anchors.

There are other very important factors such as the quality of the substrate, slope of the bottom, and depth of water to name but a few that play an important role in selecting an adequate scope.

There are downsides to larger scope such as larger swing circle.

This^.


However, this is STATIC pull data. Start horsing the anchor from side-to-side or jerk at it, and the soil will liquefy, particularly if the anchor was not deeply set. Then hold can fall of rapidly.


But in fact, the load on the anchor most nights is far less than people think, and that is why they can get away with shortcuts. It's like estimating bridge clearance or the size of waves. Unless you use a load cell, you're probably way off in your guesses. Not sayin' a safety factor isn't a good thing!

[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.

[Panope]

Originally Posted by thinwater

You cannot have a discussion of chain rode scope independent of depth...........

Absolutely.

I am remiss for not making this point clear in each of my videos.

Steve

[Stu Jackson]

Originally Posted by Mike OReilly

>>>>>>>>>>
>>>>>>>>>>>>>
and the greater the horizontal vector, the better they do this.

I believe it was Noelex (another great contributor to anchoring know how) cites research showing that rode ratios beyond 10:1 really make no measurable difference.



>>>>>>>>>>>>>


And if there's space, I happily put out more.

Horizontal is good. I try to do it every afternoon, some days more than others.


I recall that Maine Sail did one, with strings and photos, on his first website.


And yes, I read often about "crowded" anchorages. I guess I'm lucky in avoiding them. Few boats ever anchored out back in San Francisco, and I've found a great one here that scares some away because there is GASP! a rock in the entrance. For which (the rock, that is) I am grateful.