Anchors - Bigger is Better ?

[Snowpetrel]

Originally Posted by Kettlewell

This book is interesting, though it pertains to large anchors. One statement on page 82-83 stands out to me with regard to anchor efficiency: "The efficiency always decreases with increasing model size." It goes on to propose a formula for calculating the decrease in efficiency with an increase in size.

Very interesting. Thanks for posting that, table 4.3 on page 84 is exactly what I have been looking for showing powers for efficiently ranging from ^0.76 to ^1.15, or on average around ^0.95 (a dangerous assumption to average widely different soil types...) This is pretty close to the bruce anchor groups ^0.92 to ^0.94.

Also interesting that in the poorest holding the bigger anchors were more efficient ^1.15.

[Snowpetrel]

Originally Posted by noelex 77

There are two types of dragging.

The first and most common is when the anchor breaks free of the seabed. Tthe yacht drags very quickly.

The second case is when the anchor remains set, but is gradually pulled backwards.

Some sailors that have not experienced it before, fail to recognise the second form dragging. Some of the usual cues are absent.
Use all the tools at your disposal such as transits and GPS. Having an accurate GPS position of the anchor is particuarly helpful in changing wind directions.

I often drop the scale on my plotter right down to about 200 meters or so and leave the tracks on all night. If I am slowly dragging I can see the arc of my movement as the vessel yaws slowly shifting backwards. If I am holding the arc of my yawing stays put and I get a thick grouping of trails all in the same place. This arc can be used to work out where the anchor is, then you can place you anchor drag waypoint right at the anchors actual position.

I have had it where the anchor let go and then grabbed a couple of times in the night and you can see each set of arcs, in my case about 20 meters apart, each further downwind than the last.

[noelex 77]

Originally Posted by JonJo

In strong winds and a well set anchor that might be dragging - the yacht will be moving about, maybe moving through 180 degrees (because there is only one anchor set). It would be very difficult to correlate transits or GPS positions. Look at the Granny Smith vid, take a transit? When? Most people with decent anchors are too busy taking videos

A good transit can pick very small amounts of drag. It is easy test. Pick a transit and then walk forward on the boat and see when you can reliably pick there has been a change. A few meters (10 feet) should be possible.
Veering or swing is usually easily dealt with noting the maximum position backwards. For example I might conclude after watching a few swings that the lamp post should never move forward of the window edge of the house behind it.
However transits do have limitations. They don't work in a sudden wind change. Generally the boat will be moving backwards for some time as chain straightens out the new direction. (They also don't work in very low visibility, or from the comfort of your bed).
This is where the GPS is useful. If you have an accurate position centred on your anchor its possible to pick small amounts of drag (although not as small as transits) even if you boat has swung to a new location.
Many people site the in accuracy of GPS but but in practice its easy to filter out the occasional rogue position just by eye. If your plot shows a a temporary blip outside your normal swing pattern that can be disregarded.
Here is an example of a GPS plot.

Originally Posted by JonJo

But your idea that this 'well set' anchor dragging is bad - surely you do not really mean what you suggest?

If you set an anchor to, say, 500kg but the wind then loads it to 1,000kg - it will drag. It does not matter whether its a 20kg anchor or a 50kg anchor - it will drag. That drag is not 'bad' its what happens. The anchor will be pulled backward and actually will dive more deeply until it reaches that limit of 1,000kg. Its not bad, its what the anchor was designed to do. Possibly there are anchors you can set to 500kg that then do not move (if you load them further) but they have escaped my notice.

I think this is just a difference in terminology. As anchors are exposed to greater force they burry deeper. As you say they move backwards when they do this, but with a new generation anchor the movement is very little typically a foot or less.
I consider this "setting" not dragging.
A boat dragging with a set anchor is a very different scenario. Here the boat can move backwards long distances. When seen under water the anchor looks like a burrowing animal. The anchor cannot be seen, but with each gust you can see the sand disturbance above the anchor move back a few feet. Boats can drag very slowly like this for many boat lengths. Usually the boat eventually drags into deeper water and the reduced scope causes the anchor to break out.
In most ways it is much safer than the normal rapid drag, but there is the risk the skipper will be unaware of a problem.

Originally Posted by JonJo

All would be better than one big anchor (which might catch an old beer can) and have nothing else in the armoury.

Adopting the BIB approach does not limit your options. It increases them. By giving you a further option of lying to a single big anchor. This latter option is often, but not always, the best approach.
When adopting one of the other alternatives a larger anchor in the mix still provides better security. Most cruising boats have a multitude of anchors they have accumulated over the years (usually as they have gradually upgraded from standard, to big, to bigger as they cruise longer) so setting multiple anchors, or shore lines is still an option you judge that is the best approach.

Originally Posted by JonJo

To me the BIB is the marine equivalent of the urban 4X4 (say Range Rover) to collect the kids from the local school or to pick up the groceries at the local supermarket.

There is some truth in that. Most of my anchor selection advice is assuming boats are cruising and anchoring in potentially difficult conditions.
These people need the anchor equivalent of a 4x4.
We have a lot of sailors on this forum that do just that, or plan to do this style of cruising in the future. I would give racing sailors, or those that spend their time in marinas different advice (I am not implying this is any way inferior, just different, with potentially different equipment requirments)

[noelex 77]

Originally Posted by Snowpetrel

I have had it where the anchor let go and then grabbed a couple of times in the night and you can see each set of arcs, in my case about 20 meters apart, each further downwind than the last.

This sort of picture.
You can see the original arc trace in the bottom, followed by long drag to the North, another pattern produced by the boat temporally holding position, followed by a shorter third drag.

Be very wary with this once the anchor drags it rarely holds properly again as I can attest with this example. Shortly after this we went for a permanent drag and I had to stop taking photos

However you can get an identical pattern as the boat pulls the chain back following a large (especially 180degree shift in wind direction) this is where knowing the position of your anchor on the GPS plot is invaluable.
As Snowpetrel correctly points out this will be the centre of your arc, but its worth noting the position when you drop (compensate for the position of the antenna) as if the winds previously have been light and variable the arc will not be well defined.

[Kettlewell]

You guys must anchor in some pretty wide open spaces. A lot of places I anchor a GPS anchor alarm is basically useless--any movement would spell trouble, so I anchor, often using two anchors, so I don't move in the first place. I'm talking about places where I can drop the second anchor off the stern of my boat into the shallows. The first sign of dragging would be my keel hitting the ground. Sure, BIB might work if there is room for a complete swinging circle on a decent amount of scope, but there often isn't in crowded popular harbors, sometimes with strong winds against strong currents, so a more precision approach is called for, which can mean two anchors. I always get a chuckle out of these discussions of making sure you have a clear swinging radius through 360 degrees in case of a wind shift--in New England the wind frequently circles the compass several times a day, and on one side you have no water, on the other someone's fixed mooring. So much for your swinging circle.

[Visarend]

Just another 2 cents.
May I quote old Tom Cunliffe, well known seamen, instructor and YM writer:

"When I bought my old sailing pilot cutter in 1982, she was lying in the Western Isles where she had been cruising since the 1950s. Her owners were Scottish sailors of vast experience who took her 35-ton displacement comfortably in her stride.

I noted that the vessel's main ground tackle consisted of a 112 lb fisherman-style anchor and 45 fathoms of 1/2 in chain cable. 'Aha', thought I, eyeing the antediluvian gear. 'That'll need replacing with a CQR. Here's an opportunity to knock the price down a hundred quid or two'.

The owners didn't budge an inch. 'You'll find', they said, 'that the tackle works perfectly in all seabeds, including the sort of rocky rubbish we have to deal with up here in the real world'.

And so away I went, hoping for the best. After 15 years and many hundreds of nights anchored on a huge variety of bottoms, sometimes backed up by a 'chum' weight on the cable if swinging room was limited, I saw how right they were.

I never dragged that anchor no matter what the weather, come rock, mud, sand, flat, deeply sloping, or the slithery kelp from Hell.

They're awkward to stow, and they must be heavy to work properly - no use even contemplating those toys sold in chandleries where the flukes are just a bit of bent steel bar banged flat - but that's where the downside ends.

May I therefore commend the honest fisherman to you? I specified one for my new boat in 1996. It was made in Wick by the same folks who fabricate them for the RNLI, and I ship 40 fathoms of heavy chain. It has yet to drag.' (YM Febr. 2006)

BIB, BIB, BIB!

[Visarend]

Moreover...

1) the heaviest anchor and biggest and longest chain your boat can easily handle (bow volumes-bow roller and bollard strength-windlass dimensioning)

2) one of the best anchor designs

3) For long term and faraway cruising a second similar anchor stowed

4) For kedging and multiple additional needs: a Fortress with a very long scope, made ready for use.

Bon vent!

[Bash]

Originally Posted by JonJo

If you set an anchor to, say, 500kg but the wind then loads it to 1,000kg - it will drag.

Not always. Some anchors will continue to dive and set themselves deeper. This has certainly been my experience with roll-bar style anchors, and is a primary reason I'm not in the BIB camp. Were my anchor ever to drag, I would be inclined to move to the next size up. But in more than six years with this anchor it has not yet dragged, and indeed sometimes presents us with difficulty breaking it free when we want to weigh anchor.

[Kettlewell]

Not always. Some anchors will continue to dive and set themselves deeper.

What JonJo means is that every anchor that is loaded beyond its setting force drags, even if just a bit as it goes deeper. In other words, there is no such thing as an immovable anchor. Though I think Noelex better described how I think of the term "dragging":

I think this is just a difference in terminology. As anchors are exposed to greater force they burry deeper. As you say they move backwards when they do this, but with a new generation anchor the movement is very little typically a foot or less.
I consider this "setting" not dragging.
A boat dragging with a set anchor is a very different scenario. Here the boat can move backwards long distances.

The one thing that can muddy these waters a bit is when you have a very soft bottom and a lot of force, like you might get in the Chesapeake. There it can feel like you are dragging when a big wind moves your boat backwards, but eventually you come to a stop after your diving anchor, like a Fortress or a Danforth, goes down another 10 feet or so to stronger holding ground. And, then there are some substrates that are so deep and oozy, for want of a better term, that you can have a perfectly set anchor and it just won't hold beyond a certain point. Once you get beyond the force this ooze will take almost anything drags--the only cure is to gain surface area on your anchors.

[Bash]

Originally Posted by Kettlewell

What JonJo means is that every anchor that is loaded beyond its setting force drags, even if just a bit as it goes deeper. In other words, there is no such thing as an immovable anchor. Though I think Noelex better described how I think of the term "dragging"

Interesting. If this is the case, I'm going to have to disagree with how JonJo defines dragging. An anchor setting itself more deeply is not dragging.

[DumnMad]

This is a cruisersforum. BIB is good advice for wannabee cruisers. Arguing that size doesn't make much difference is bad advice. Cruisers can die because anchor is too small while a day sailor can go out with no anchor. In some places near us just the chain dropped into the mud will anchor just fine, but it doesn't deny BIB.

[Kettlewell]

First of all, very few cruisers die while cruising of any cause, and I'm pretty sure most of the time it is falling overboard and drowning. Not many die due to an anchor dragging. Second, since when is anyone advocating an anchor that is "too small?" The question is if BIB is really overkill and possibly counterproductive in some circumstances.

[sailorboy1]

Originally Posted by Kettlewell

The question is if BIB is really overkill and possibly counterproductive in some circumstances.

So while I have not read every post, it appears that after post 642 we are back to post #1.

Has an answer been established yet?

[Kettlewell]

Has an answer been established yet?

Has an answer ever been established in an anchoring thread?

[Cotemar]

Originally Posted by Don L

So while I have not read every post, it appears that after post 642 we are back to post #1.

Originally Posted by Don L

Has an answer been established yet?

Yes. The answer is that JonJo (the OP) is the only one that likes small anchors.
All 99.999999999 % of the other cruisers use a BIB anchors.

JonJo is the only cruiser I know that also runs his bridle from his stern cleats to his bows. He does things differently, but for the rest of us we tend to use what 99.999999999 % of other cruisers use since we all like to go with experience and not theory.

No worries, it works for him.

After 644 posts, he never did sell the small anchor theory to anyone.