Anchoring with 4:1 Scope?

[noelex 77]

The modern development of powerful and reliable anchor windlasses has enabled even small crew to manage large anchors.

This has opened up the possibilities of using smaller scopes than have traditionally been advocated. This is championed by Steve Dashew with his very large primary anchor (250lb on a relatively low windage 64 foot power boat) . As Dockhead pointed out in a previous post on this thread, Dashew often uses much shorter scopes than most of us would routinely adopt (he reports regularly using 2.5:1).

Interestingly, my impression is that scopes used by cruising sailors are gradually increasing rather than decreasing over the years.

Having said that, I am writing this anchored at around 10:1 (although this will decrease at high tide to around 7:1). Why not? In this remote area we have not seen another boat anchored for over three months so we are unlikely to inconvenience anyone else and there is ample swinging room.

However, the ability to safely anchor at shallow scope, (using judgement and prudence) when this is appropriate, is a valuable asset. It enables the skipper to utilise anchorages and anchoring possibilities that would otherwise not be possible.

This advantage is not just limited to small scopes. For example, a larger anchor at 4:1 may have the same holding power as an otherwise identical small anchor at 7:1. There are plenty of anchorages and situations where 4:1 is practical, but not 7:1.

[sailorboy1]

I also let out a lot more scope if I have the swing room. Why not as it only takes an extra minute or two for the windlass to bring it back up (and yes I have had to bring it up by hand once when solo). But I still end up with something in the 5-7:1 with a normal of around 7:1 even though I know I don't really need that much most times.

There is the old true saying; the chain wouldn't help you if it is still in the locker

Interesting with all the times I have anchored on long scope in a blow the hardest time I ever have had in freeing the anchor was after a couple days at a 3:1 scope. Just shows that the bottom factors in more than the scope, at least for my oversized Manson Supreme anchor.

[Mike OReilly]

I'm with Noelex, and most others, with his approach. Unless I'm constrained by geography (which happens sometimes) or close proximity of other boats (which happens rarely), I will usually put out at least 7:1, and often more. Unless you're needing to make a fast exit, why would you not?

In areas where I am constrained, I'll set less (of course), but this is when choices are limited. I try and avoid these kinds of anchorages as much as possible.

Large anchors and heavy chain definitely do give a wider margin of error when it comes to staying put. This is why I always advocate for installing the largest new-gen anchor your boat and crew can reasonably manage. Again, why would you choose smaller if you can just as easily manage a larger anchor? The point is to have as much holding power as is reasonably possible (otherwise, why get a bigger anchor?).

The same rational applies to scope; why would you put out less if more is possible? Perhaps if you know most of the variables, then a more narrow calculation can be made. But those who anchor in a wide variety of challenging places simply can't know everything.

[rslifkin]

Originally Posted by Chotu

I have a logical question for the short scope crowd:

Other than a crowded anchorage or a spot where you are trying not to swing into a hazard, what is the goal?

It all depends on where, when, and how long I'm staying for me. Overnight, the minimum I'm comfortable with in a given set of conditions is longer than if it's just a daytime stop.

During the day in deeper water, if the wind is a bit gusty (but not too strong) I'll sometimes keep things a bit short. My boat sails around quite a bit at anchor unless the wind is perfectly steady in both direction and speed (and I've yet to find a good way to settle it), so shorter scope tames the sailing a little and reduces the speeds it can attain before pulling the rode tight and tacking.

I'll also go shorter for a daytime stop in busy places to keep my rode angle a bit steeper and reduce the risk of some idiot running it over (I've had people in small day boats get uncomfortably close to my rode many times, as they seem to forget that we don't all drop our anchors straight down).

Other times, I shorten up to keep my swing small because I'm tucked into a tight area and don't want to swing too close to a shallow spot or something, but I'd only do this for an overnight if I didn't have a better option.

And if I'm just stopping for an hour or 2 to watch a sailing race or something, especially in deep-ish water, dropping a bit less rode means a little less time standing on the bow holding the windlass remote, particularly if a need to move quickly comes up.


When I sized my anchor, I did size it a bit large. One reason was sitting out a good thunderstorm in a mediocre bottom. I ended up with a 73lb Vulcan on a 38 foot moderate windage boat that's about 26k lbs loaded. That sizing leaves enough margin to shorten scope a bit in a decent bottom and half-decent weather. Even in kinda iffy bottoms (weedy with some kind of sandy mud substrate of unknown quality) at short-ish scope (4:1 in 11 feet of water, so 70 feet of chain with a 25 foot snubber) I've had the thing set solidly enough that it took a decent bit of effort to break the anchor out.


I do carry a good bit of rode to allow plenty of scope when there's not a reason to go shorter. Current rode is 90 feet of chain and 300 of nylon, so about 375 feet usable. If our cruising grounds become a bit more varied or when I have a reason to change something, I'm considering changing the setup to 150 feet of chain, 250 of line (line type TBD).

[Chris Cringle]

One must be VERY careful when using a 20th century anchor on a 21st century bottom. Remember that in the old (that word gives me shivers) days, geezers went to sea in "boats" designed by nautical architects and built by shipwrights and made from old (that word again) trees. These people relied upon ideas handed down from even older people! But today! We can buy a "perfect combination of performance and entertainment platform" designed by a computer and "crafted" by a 'state of the art' factory of space-age material. The obsolete old fashioned ocean is no place for these modern marvels, nor are archaic anchors. They simply won't work! And who has time to crank up all of that cable? So, when the full-page ad in the latest edition of your favorite sailing magazine tells you that thier new smart-anchor needs only a two to one scope, who are you going to believe? Some crusty old goat wearing worn-out Sperrys or the cutting edge whiz kid with his electro-polished stainless steel Starship Enterprise Special?

[Dockhead]

Originally Posted by Chotu

I have a logical question for the short scope crowd:

Other than a crowded anchorage or a spot where you are trying not to swing into a hazard, what is the goal?

If you are trying to put out the minimum scope you can get away with, you’re factoring in:

*bottom type
*expected weather
*unexpected weather
*if it’s good holding ground exactly where you dropped it
*current

Say you tally all that up and determine everything is favorable so you can get away with 4:1. Or maybe it’s really favorable and you can do 3:1.

But then 2 days later, a front passes and you end up with 40 knot winds.

You now have diff conditions and decide to increase the scope to 5:1 because all the factors you consider say it’s not ideal for 3:1 anymore.

Ok, no problem. Just let some more out, right? Easy!

But why?????

Why not just set the anchor for its best performance when you arrive and forget about managing the anchor?

I dump out 10:1 not because I need it on nice calm days. I dump it out so when a surprise thunderstorm comes flying through while I’m ashore, the boat stays put. So I can sleep through truly insane weather soundly, safely and in comfort and security.

But what’s the main reason I dump out 10:1?

Because I’m lazy!

I’d rather do other things than manage my anchor system constantly. 10:1 is “set it and forget it” scope. Like an autopilot for your anchoring system.

Why do you all want to pay this much attention to your anchoring system? That’s the part I just can’t wrap my head around.

Do you not use the autopilot when underway? Do you prefer to be more deeply involved in the management of things on the boat than to have automatic systems? Does it make boating more enjoyable to keep track of things like this?

It might for some people and I can understand if it does. Then I would understand the short scope and playing with the scope as conditions change.

In my lazy world, I dump it overboard at 10:1 and don’t think about it again until it’s time to pull it back up. For weeks. No matter what the weather, all the way up through named storms. I check for chafe once a season or so if it’s been particularly brutal out. That’s it. Otherwise, the anchoring system is not in my thoughts.

I think everyone puts out more chain if there is plenty of room in the anchorage. Why not? 10:1 is overkill but 7:1, 8:1 -- why not?

My anchor is sized however so that the holding power at 3:1 exceeds the holding power of a normal sized anchor at 10:1. It's two sizes oversized. Therefore, 3:1 is perfectly fine if I don't have the room to swing to more. Even in bad weather, if the bottom is decent.

A bigger anchor gives you these options.

I went through a pretty bad storm at about 2.3:1 once. I didn't have any choice -- it was in the Arctic, in Greenland, where the bottom slopes with extreme steepness and there is hardly any place to anchor. Very rarely you can find a bit of flat bottom at the end of a cove, and that was what I had that time, with like 40m of water and 100m of chain on board.

It's a good thing that I had experience and knew that the anchor would hold at that scope. And it did.

[Dockhead]

Originally Posted by noelex 77

. . . However, the ability to safely anchor at shallow scope, (using judgement and prudence) when this is appropriate, is a valuable asset. It enables the skipper to utilise anchorages and anchoring possibilities that would otherwise not be possible.
. . .

It also helps you make good decisions about anchoring.

A sailor who only knows that more scope is better, might choose a poor bottom but in water shallow enough to get to 10:1 scope (and we had folks on here a few years ago even arguing for anchoring off a lee shore in order to achieve that). Or even worse -- choose a sloping bottom. When they might be able to hook into excellent low lying silt in the middle of the cover, but where it is so deep that you won't achieve more than 3:1 or 4:1.

These are bad decisions. Give me the excellent bottom in the middle of the cove, with flat bottom, on 3:1, over iffy holding on the slopes going down to that place, on 10:1, any day. Adding to the rationality of this approach is the fact that shorter scopes seem to work better in very deep water. If all you know about anchoring is that more scope is better, then you will make the wrong decision in this situation, which is quite a common one in some areas.

In my view, flatness of the bottom -- something we don't talk about much on here, is VASTLY more important than scope. I will do almost anything to avoid anchoring in a sloping bottom. Sometimes you have to anchor in very deep water to find that.

[Pandor]

People who don't think 10:1 or more is an issue for fellow sailors are the same types that park over two spaces.

[Dockhead]

Originally Posted by Pandor

People who don't think 10:1 or more is an issue for fellow sailors are the same types that park over two spaces.

Indeed. I put out 10:1 from time to time, but only when I expect really bad weather.

And ONLY in empty, spacious anchorages. Putting out 10:1 in a crowded anchorage is piggish behavior.

[thinwater]

Originally Posted by Pandor

People who don't think 10:1 or more is an issue for fellow sailors are the same types that park over two spaces.

Or they park at the far end of the lot, leave space, and arn't afraid to walk a little farther. Not everyone vultures for spots near the landing. Don't paint all people with one brush.


And Dockhead is dead on when he states that the bottom type outweighs all other considerations (not including pointless exaggerations, common in anchoring threads).


And personally, bully for Chotu for saying what many are thinking. It isn't just scope. Extra chain on the bottom also buffers wind changes. (The down sides have been stated.) What if a 50- to 70-knot squall comes up while you are ashore (no one there to let out more scope)? I've had that happen a number of times in the summer. In unstable weather, that is what I anchor for.

[boatman61]

Originally Posted by Pandor

People who don't think 10:1 or more is an issue for fellow sailors are the same types that park over two spaces.

Yeah.. it really tee's me off when I arrive in a busy Anchorage and all the folks on 5, 6 or 7 to 1 scopes won't shorten down to 3 or 4 to 1 to make room for me..

[Jetx]

Originally Posted by SV Siren

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..

I think it’s been shown that a kellet won’t help with holding (not enough weight to make a meaningful difference to catenary). We’ve used one on the past with all-nylon rode, to prevent rode from wrapping around the keel in shifty conditions, but with all chain rode, I wouldn’t bother. It’s just another thing to mess with, potentially wrapping your chain and causing retrieval difficulties, for no real benefit.

[Don C L]

Originally Posted by Dockhead

I went through a pretty bad storm at about 2.3:1 once. I didn't have any choice -- it was in the Arctic, in Greenland, where the bottom slopes with extreme steepness and there is hardly any place to anchor. Very rarely you can find a bit of flat bottom at the end of a cove, and that was what I had that time, with like 40m of water and 100m of chain on board.

It's a good thing that I had experience and knew that the anchor would hold at that scope. And it did.

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.)

[hpeer]

Dockhead wrote:

My anchor is sized however so that the holding power at 3:1 exceeds the holding power of a normal sized anchor at 10:1. It's two sizes oversized. Therefore, 3:1 is perfectly fine if I don't have the room to swing to more. Even in bad weather, if the bottom is decent.

Thats how I got to q 125# Mantus. My chain only does me good if I can deploy it. The extra anchor weight is going to do me good every time I deploy it. Then put out as much chain as I can get away with, within reason.


I think it helps to brea the anchoring system down into these very general segments.

The anchor connects to the bottom.
Shackle connects chain to the anchor
Chain helps keep anchor shank down
Deck tackle connects chain to boat
Snubber adds elasticity to chain to avoid shock loads

A heavier, better design anchor will connect better than a small one.
The chain connection, no matter how much rode, can only provide some percent of the anchors holding strength.

Anchor A will provide 2,000# in a certain bottom
Anchor B will provide 1,000# in that same bottom
7:1 scope will provide 70% of either
5:1 scope will provide 50%

So for a given scenario where you are limited to 5:1 scope Anchor A will give you 1,400# and B 1,000#.

Numbers fudged a bit to make math easy, just to illustrate the point.

[Kelkara]

Originally Posted by Dockhead

I went through a pretty bad storm at about 2.3:1 once. I didn't have any choice -- it was in the Arctic, in Greenland, where the bottom slopes with extreme steepness and there is hardly any place to anchor. Very rarely you can find a bit of flat bottom at the end of a cove, and that was what I had that time, with like 40m of water and 100m of chain on board.

This got me thinking ... In that situation, my first thought would be to shackle my second anchor rode onto the primary to increase scope. I'm sure your boat has a second anchor, so if that option was a sensible choice you would have thought of it ... could you explain your reasoning for selecting short scope instead? was it because there was no room to swing, or because joining the rodes was impractical in storm conditions, or because you'd rather the risk of dragging than the risk of losing both anchor rodes if you have to cut loose, or because you had plenty of experience with that anchor at 2.3:1 in "pretty bad storms" and totally trust it, or is your ground tackle so oversized that it would hold a battleship on any scope, or do the "rules" change at depths of 40+m?