anchor scope

[sailorboy1]

Originally Posted by Kettlewell

I find it hard to believe that Don wrote that because he's wrong, and he's usually right! There are lots of studies on this. It not only improves the angle of pull at the anchor, but it reduces the load on the anchor by putting either additional catenary and/or additional stretch in the line. Yes, catenary does go away after a certain load is reached, but it does have an effect at normal wind speeds. Besides, I have seen it in action hundreds or thousands of times when I've dropped anchors and played with the scope--too little and it doesn't hold so well, let out more the anchor holds just fine. I also see it in action every weekend in places like Cuttyhunk where due to the crowded conditions a lot of people short scope it and drag anchor during the 2am wind shift or thunderstorm.

Here's our own JonJo's article on this in Practical Sailor.

I'm neither right or wrong, I just asked a question.

This is the first I've seen this article. But it doesn't seen to be what my question was. The article near as I can understand (because I read the beginning and skipped to the answer) is about shock loads and the conclusion was that the loads are highest at 3:1.

My question was about what I read in Sail that said the after 4:1 there wasn't any benefit to higher scope. Is this true that a 6:1 scope will not hold better than a 4:1? Are there any tests about holding and scope?

PS - It isn't me saying 4:1 is the right answer.

[Kettlewell]

By "Don" I meant "Don Casey," not you. Sorry. Read that JonJo article more closely. He does point out that there are much lower loads on the anchor at increased scope, so an anchor would hold better with less load, wouldn't it?

[Cotemar]

I use 5-1 in tight anchorages

7-1 if their is room

10-1 in a storm

If Jonjo is in the anchorage I will take a mooring, so as not to move any soil around the anchorage. But that is just me

[Zednotzee]

I read the same article (March issue), & he makes a good point I think. Increased scope is no replacement for a properly sized anchor, & only changes the load from vertical to horizontal.

He also points out that the rode itself has no holding power whatsoever.

[SailFastTri]

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?

For those who want scientific evidence that is "bunk", the following link is probably the definitive online engineering article:

Tuning an Anchor Rode

[Tomm0]

Originally Posted by David M

Scope is not a new term, at least in the US. It is the ratio of anchor rode out to water depth.

It you're all-chain, you have no rode... Technically.

[Zednotzee]

Originally Posted by Don L

My question was about what I read in Sail that said the after 4:1 there wasn't any benefit to higher scope. .

What he actually says is: "Bear in mind that increasing scope does not decrease total load on the anchor. It merely makes the load more horizontal. Doubling scope from 4:1 to 8:1 transfers around 9.3% of the total load from vertical to horizontal. Tripling scope shifts just 12.8% of the load"

So it's not that there's no benefit, just a diminishing return.

[boatpoker]

Many years ago I believe even Power Squadron taught 5:1. Somewhere along the line they changed to 7:1. I have often anchored with as little as 3:1 quite comfortably in the ICW or offshoots thereof. In Georgia we sometimes went to the side of channel and stepped off onto the shore carrying a bow and stern anchor which we pushed into the mud.

Our basic rule is l... let out as much as you have room for but conditions and location count much more than any set formula.

[Kenomac]

Originally Posted by Cotemar

I use 5-1 in tight anchorages

7-1 if their is room

10-1 in a storm

If Jonjo is in the anchorage I will take a mooring, so as not to move any soil around the anchorage. But that is just me

Same here. All chain

[Bash]

Originally Posted by Tomm0

It you're all-chain, you have no rode... Technically.

No no no no no no no. The rode includes the anchor shank, the shackle, the chain, and any ropey stuff as well. And a swivel if you've got one.

Common misconception that "rode" only denotes the ropey stuff.

[Kettlewell]

rode 2 (rd)
n. Nautical
A cable, chain, or rope, especially one attached to the anchor of a small boat.
[From Middle English at rode, at an anchorage, from rode, a riding; see road.]


The American Heritage® Dictionary of the English Language, Fourth Edition copyright ©2000 by Houghton Mifflin Company. Updated in 2009. Published by Houghton Mifflin Company. All rights reserved.

Rode includes the chain and rope, but not the anchor shank.

[Tomm0]

Better reference?
Not how I've ever used the word except when using an all-chain rode.

[Bash]

Originally Posted by Kettlewell

Rode includes the chain and rope, but not the anchor shank.

I'm not on the boat at the moment. Anyone got a copy of Chapman's Piloting handy? If so, please check the glossary: we're looking for an authoritative definition of "rode."

[Kettlewell]

How about Chapman's?

All of the gear, taken collectively, that lies between a boat and her anchor is called the RODE--whether it be synthetic fiber (like nylon), chain, wire, or a combination of fiber and chain.

[Bash]

Originally Posted by Kettlewell

How about Chapman's?

Okay. I'll give you that one. A somewhat modern definition, and maybe a little small-boatish, but I'll give it to you.

Forget the shank, if you must, BUT INCLUDE THE CHAIN...

and the shackle

and the swivel

and all that other gear that contributes to the rode's length.