Anchors!

[GHA]

However, for those with more usual anchoring gear it is wrong to dismiss scopes of less than 5:1 as “dangerous nonsense”. With judgement, scopes of less than 5:1 are fine to use if the circumstances are appropriate. Scopes less than 5:1 are not particularly unusual.

:encouragement::encouragement:

"With judgement" being the meat of the matter

 

[webcraft]

Jonathan, when using a 15kg (or 8kg aluminium) anchor and 6mm chain on a 38 foot catamaran I can understand your refusal to use scopes of less than 5:1. I also think your other precautions such as setting two anchors in wind above 30 knots is entirely sensible and prudent given your equipment.

However, for those with more usual anchoring gear it is wrong to dismiss scopes of less than 5:1 as “dangerous nonsense”. With judgement, scopes of less than 5:1 are fine to use if the circumstances are appropriate. Scopes less than 5:1 are not particularly unusual.

+2

A scope of 4-1 is standard for our Spade unless very strong winds are forecast. Setting 5-1 or more requires a huge amount of chain if there is much tidal range. (I am assuming the 'long-scopers' do actually calculate the scope for high water and allow another metre for the drop from bow roller to water surface)

Round here tidal ranges are relatively low, but let's suppose I anchor in 3m at low water Springs. Add another meter for the distance from bow roller to water, plus 4m for the rise of tide plus a metre for luck/atmospheric conditions. This gives 9m, so at 4-1 I need to put out 36m of chain - which is a meter more chain than we carry (though there is 25m of octoplait spliced on)

Imagine adding 3m or more to this for folk further South in the Irish Sea (and we won't mention the Bristol Channel or the Channel Isles) and you are starting to talk about small yachts carrying an unfeasibly large amount of chain if 5-1 is your minimum scope.

I shall continue to use 4-1 as standard and 3-1 in calm weather/crowded anchorages - always making the appropriate adjustments in my calculations as detailed above.

- W

 

[thinwater]

Please list the depth and rode type when describing scope. Without this information the examples are very hard to put into perspective.

Scope is only one variable in the equations that determine lead angle at the anchor.

---

I'll give you one more thing to think about. What if I anchor in very soft mud in shallow water, at short scope. The water is 5 feet, the bow is 3 feet. I anchor at 4:1 using 32 feet of rode. But the anchor needs to dig in digs in 3 feet to reach firm mud (true). Now the scope is actually 3:1, plus the mud has curved the chain, resulting in a true angle at the anchor of less than 2:1. No anchor can dig with a true lead angle that high.

Yes, this is outside of the common experience, offered only to point out why you need to give more information. This place is not contrived but was actually used for a large anchor test. In many trials the anchors went deeper than 3'.

 

[Neeves]

Jonathan, when using a 15kg (or 8kg aluminium) anchor and 6mm chain on a 38 foot catamaran I can understand your refusal to use scopes of less than 5:1. I also think your other precautions such as setting two anchors in wind above 30 knots is entirely sensible and prudent given your equipment.

However, for those with more usual anchoring gear it is wrong to dismiss scopes of less than 5:1 as “dangerous nonsense”. With judgement, scopes of less than 5:1 are fine to use if the circumstances are appropriate. Scopes less than 5:1 are not particularly unusual.

We always set our anchors at 3:1 - simply laziness - if the anchor does not set, for any reason, there is less chain to retrieve and try again. If for lunch we will leave the scope at 3:1. Otherwise we will deploy more chain seldom more than 5:1.

Our tides are a maximum of 2m (but can be 300mm on Tasmania's west coast - atmospheric condition can impact the tidal range). We would normally plan to anchor in 5m depth, high tide (add 1m to bow roller) We would try to anchor close to the beach - because many of the anchorages are low lying and have limited shelter from wind. We are thus commonly deploying 30m of chain (we carry 75m). We would not anchor in less than 2m of water (low tide), we draw 1m - because that brings us too close to the beach and breaking waves or the chop building as the water shallow.

We anchor in locations with swell and waves (many of Australia's east coast anchorages are fully exposed to swell from the Tasman Sea) and if winds are forecast to be more than 25 knots we would commonly deploy 2 anchors in a fork/V - its not a hassle, its easy. But in an ocean anchorage having swell seeping into the bay and having a developed chop would not be unusual.

We seldom see other yachts in the same anchorages and if there are 3 yachts - they can be a considerable distance apart - many 100's of metres (most of the bays are huge, Trail Bay is a good example). We have no issues with space.

BUT if any of these bays were to be full we would never, ever, consider under any circumstances to anchor at less than 3:1 with swell and an opposing chop and with winds forecast over 25 knots (which would commonly mean gusts of 35 knots (winds measured at the masthead).

Why the caution - we once enjoyed a forecast of 25 knots and had the pleasure of winds over 50 knots for 7 hours. We don't take, nor need to, chances

A common practice seems to be a scope of 3:1 which implies to me that short scope would be less than that - so unless anyone produces evidence of success - at plus 25knots with a bit of chop and swell - then suggesting safety at less than 3:1 (i.e. shorter than seems to be accepted) its dangerous nonsense.

If 3:1 is considered short scope - you don't need an oversized anchor - lots of people do it (evidenced here) as standard practice without the need to double anchor size.

Adding to Thinwater's comments - the east coast of Australia is endowed with many navigable rivers, which can have challenging bars and might not be for the faint hearted. Many of these rivers host oyster farms - and have mud bottoms. We also have a lot of mud in our flooded rias, Pittwater, our local waters, are an example - but these are much more sheltered and different practices would be used.

I consider short scope at anything below 3:1 (which would be our minimum (even in a river).

Jonathan

 

[MagicalArmchair]

We always set our anchors at 3:1 - simply laziness - if the anchor does not set, for any reason, there is less chain to retrieve and try again. If for lunch we will leave the scope at 3:1. Otherwise we will deploy more chain seldom more than 5:1.

Our tides are a maximum of 2m (but can be 300mm on Tasmania's west coast - atmospheric condition can impact the tidal range). We would normally plan to anchor in 5m depth, high tide (add 1m to bow roller) We would try to anchor close to the beach - because many of the anchorages are low lying and have limited shelter from wind. We are thus commonly deploying 30m of chain (we carry 75m). We would not anchor in less than 2m of water (low tide), we draw 1m - because that brings us too close to the beach and breaking waves or the chop building as the water shallow.

We anchor in locations with swell and waves (many of Australia's east coast anchorages are fully exposed to swell from the Tasman Sea) and if winds are forecast to be more than 25 knots we would commonly deploy 2 anchors in a fork/V - its not a hassle, its easy. But in an ocean anchorage having swell seeping into the bay and having a developed chop would not be unusual.

We seldom see other yachts in the same anchorages and if there are 3 yachts - they can be a considerable distance apart - many 100's of metres (most of the bays are huge, Trail Bay is a good example). We have no issues with space.

BUT if any of these bays were to be full we would never, ever, consider under any circumstances to anchor at less than 3:1 with swell and an opposing chop and with winds forecast over 25 knots (which would commonly mean gusts of 35 knots (winds measured at the masthead).

Why the caution - we once enjoyed a forecast of 25 knots and had the pleasure of winds over 50 knots for 7 hours. We don't take, nor need to, chances

A common practice seems to be a scope of 3:1 which implies to me that short scope would be less than that - so unless anyone produces evidence of success - at plus 25knots with a bit of chop and swell - then suggesting safety at less than 3:1 (i.e. shorter than seems to be accepted) its dangerous nonsense.

If 3:1 is considered short scope - you don't need an oversized anchor - lots of people do it (evidenced here) as standard practice without the need to double anchor size.

Adding to Thinwater's comments - the east coast of Australia is endowed with many navigable rivers, which can have challenging bars and might not be for the faint hearted. Many of these rivers host oyster farms - and have mud bottoms. We also have a lot of mud in our flooded rias, Pittwater, our local waters, are an example - but these are much more sheltered and different practices would be used.

I consider short scope at anything below 3:1 (which would be our minimum (even in a river).

Jonathan

With my Rocna, in 8 meters at high water I chucked out 30 meters of chain, so 3.75:1 scope at HW, when the tide was out, I was in 3 meters, giving me a scope of 10:1. Hmm, is that poor anchoring? Conditions were glassy, holding well known, beautiful gloopy East Coast mud.

 

[thinwater]

With my Rocna, in 8 meters at high water I chucked out 30 meters of chain, so 3.75:1 scope at HW, when the tide was out, I was in 3 meters, giving me a scope of 10:1. Hmm, is that poor anchoring? Conditions were glassy, holding well known, beautiful gloopy East Coast mud.

Actually, only about 3:1 scope, since we need to include the height of the bow roller and the depth the anchor buries.

There are two cases represented here:
* Deep water, short scope
* Shallow water, long scope

The key, in moderate conditions, is the amount of chain, which can provide catenary. In strong conditions (over 30 knots) the chain would straighten out and this would be sub-standard at high tide, but the chain would be on or near the bottom in lighter winds. Much depends on how predictable the weather is and what you will hit if you drag.

No, that would not give me warm fuzzies, but it could be OK. But remember, experiences are different. For example, an hour ago a squall came through here, and the wind went from 5 knots to >50 knots in less than a minute. There were tornado warnings.

 

[Neeves]

As Thinwater says - its about how much catenary remains under the worst of the conditions in which you are anchored. And rather than scope the appearance of the chain is a better indication as a heavy chain at the same scope as a light chain will show markedly different 'degrees' of catenary. If your chain looks as straight as a die (it won't be but is as goods as) then you will experience snatch loads as your yacht yaws and horses. Your chain will look straight, if the chain is not overly heavy, you have a reasonable scope 4:1/5:1, and you are anchored in around 5m-7m bow roller to seabed - for most yachts at around 30 knots and if you have high windage 25 knots. If the chain is heavy, or light (small chain, mixed rode) the windspeed will be slightly higher/lower.

Below around 20 knots, same conditions, you will have some chain on the seabed. With 8mm chain, 30m deployed at 5:1 all the chain will be off the seabed at around 17 knots and the final link or shackle - just 'kissing' the seabed (the tension is around 70kg - about what a fit man can hold). I have not checked but at 3:1 scope you would have only 18m deployed - the catenary would be more straight, the shackle angle would be higher - I'd hesitate to suggest you would be comfortable in 30 knots. From actual testing I would say snatch loads at 30 knots would be 200/300kg - you would certainly notice (unless you have a really good snubber)

You can reduce the impact of yawing, a major cause of anchors dragging, by using 2 anchors in a 'V/fork.

You can reduce the impact of yawing and horsing by using a decent snubber (or bridle). By using 2 anchors both of which have some elasticity, joined to a common bridle, mixed rode with a textile part being elastic or 2 bridles/snubbers you can remove snatch loads completely. You can reduce yawing by using a riding sail (not very fashionable) - there is no one answer (though you could use them all in combination).

Jonathan

 

[Mark-1]

Finally, let's talk common sense. I want my anchor to hold a few tons in storm conditions. I then want to be able to recover the anchor without undue ceremony. This depends the anchor releasing at short scope. Recall the horror stories of recovering Fortress anchors after a storm. A windlass won't even wiggle it, an running over it just once or twice won't either. They are perhaps the only anchor out there that really holds at short scope--hard recovery is obvious proof. But is that really something you want? Perhaps the best anchor, for most of us, is one that is strong and resets well at long scope, and releases easily at short scope.

I'd never considered that compromise before, thanks.

 

[NormanS]

I'd never considered that compromise before, thanks.

I have anchored thousands of times, with a variety of anchors, in all sorts of conditions, and have never failed to retrieve my anchor. I find that shortening right up, so that the chain is vertical, and giving it time, the buoyancy of the boat will eventually free any anchor from mud, even my Fortress. Obviously, if your anchor is caught under an immoveable object, the situation is different, and requires a different solution.

 

[Mark-1]

I have anchored thousands of times, with a variety of anchors, in all sorts of conditions, and have never failed to retrieve my anchor.

So, you have never needed to consider that compromise, either. No doubt you are also grateful to thinwater for raising it.

 

[Kukri]

I have anchored thousands of times, with a variety of anchors, in all sorts of conditions, and have never failed to retrieve my anchor. I find that shortening right up, so that the chain is vertical, and giving it time, the buoyancy of the boat will eventually free any anchor from mud, even my Fortress. Obviously, if your anchor is caught under an immoveable object, the situation is different, and requires a different solution.

I lost a Danforth to a ground chain, years ago. The thing just clamped its jaws on the chain and would not let go. I waited till low water and was able to sight it, get a line round the ground chain and bash it hard but even that would not free it. It's probably still there. With CQRs the Hiscock loop of chain trick has always worked for me and I assume it will work for most if not all of the modern anchors.

 

[thinwater]

I have anchored thousands of times, with a variety of anchors, in all sorts of conditions, and have never failed to retrieve my anchor. I find that shortening right up, so that the chain is vertical, and giving it time, the buoyancy of the boat will eventually free any anchor from mud, even my Fortress. Obviously, if your anchor is caught under an immoveable object, the situation is different, and requires a different solution.

Neither have I. As you say, the solution is normally to get right over it and let the waves work on it. And yet I know that in general a scoop anchor is a lot easier to recover than a pivoting fluke anchor after equivalent wind, and for every day anchoring, that is something in favor of the scoop (Manson Supreme most resently). I also love my Fortress (I've had them on three boats) as a secondary.

My point was that there is a direct relationship between ease of recovery and short scope capability. Logically, this is almost an identity.

I see it as one of the many compromises we must balance.

 

[Mark-1]

I lost a Danforth to a ground chain, years ago. The thing just clamped its jaws on the chain and would not let go. I waited till low water and was able to sight it, get a line round the ground chain and bash it hard but even that would not free it. It's probably still there. With CQRs the Hiscock loop of chain trick has always worked for me and I assume it will work for most if not all of the modern anchors.

I once had a Bruce drop into massive crack in the rock seabed. A mini-cave really. The anchor went down through it but clearly wasn't ever going to find its way out. I swam down 8m and manoeuvred it out manually.

If it had been 8.5m it would still be there.