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Old 25-09-2017, 09:21   #1
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Tandem anchoring

Many years ago I read an article about tandem anchoring.
The set up is that the first anchor would be connected to a second anchor with about 20 foot of chain, the object to increase the holding power rather than double anchoring.
Has anyone tried this setup with good or bad results?
Thanks. Nick
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Old 25-09-2017, 09:25   #2
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Re: Tandem anchoring

Try a search - there was a long thread on this a couple of weeks ago. To summarize: nobody seems to think it's a good idea, for a number of well-explained reasons.
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Old 25-09-2017, 09:55   #3
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Re: Tandem anchoring

Yes, Iíve done this ó exactly once. It was with a CQR as the main, and I used a smaller Bruce as the kellet. It was in preparation for a big blow coming through and it worked fine.

Iím no fan of this kind of approach though. Iíd much rather have the largest new-gen anchor as my bower, along with good rode (all-chain) along with stout snubbers. This is what I have now and it has never let me down.
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Old 25-09-2017, 10:34   #4
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Re: Tandem anchoring

There is no perfect anchoring technique, but as general rule tandem anchoring is difficult to implement successfully.

Arranging the anchors so that both are contributing effectively is difficult and the danger is that the better anchor may be hampered. This can result in less holding than the better anchor used on its own.

This is an example of one such fail I observed underwater. The anchors have been rigged poorly with an incorrect attachment, but the Rocna is not contributing to the holding. It was not even touching the substrate most of the time.



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Old 25-09-2017, 10:41   #5
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Re: Tandem anchoring

Quote:
Originally Posted by noelex 77 View Post
There is no perfect anchoring technique, but as general rule tandem anchoring is difficult to implement successfully.

Arranging the anchors so that both are contributing effectively is difficult and the danger is that the better anchor may be hampered. This can result in less holding than the better anchor used on its own.

This is an example of one such fail I observed underwater. The anchors have been rigged poorly with an incorrect attachment, but the Rocna is not contributing to the holding. It was not even touching the substrate most of the time.



Was this intended as a demonstration of bad anchoring? I can't imagine anyone thought this would work.
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Old 25-09-2017, 10:51   #6
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Re: Tandem anchoring

My guess is to be effective you'd be better with them on a Y chain or cable rather than in series.
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Old 25-09-2017, 10:57   #7
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Re: Tandem anchoring

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Originally Posted by LoudMusic View Post
Was this intended as a demonstration of bad anchoring? I can't imagine anyone thought this would work.
I did have a brief talk with the owner about anchoring technique . When I saw the boat again they used the same set up , although they may have at least changed the attachment point, which would have been a major improvement.

On the second occasion the Rocna set (and set very nicely). The Brittany was contibuting very little to the holding.

The difficulty of tandem anchoring, or any technique that uses two anchors even on an independent rode, is getting the anchors to share the load. It is very difficult, so in practice there is often little improved holding power, and a lot of extra complication, over the results seen with the better anchor alone.

Two anchors, especially rigged on two rodes, can be useful to limit the swing, or for example, to point the bow into swell. Unfortunately, often two anchors are deployed, in all sort of set ups, in the hope of increasing the holding power. The results do not often achieve this aim.
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Old 25-09-2017, 11:07   #8
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Re: Tandem anchoring

It never works that way the articles say. I've done a lot of anchor testing, and I tried everything to make it work. It is myth.

  • If the scope is less than 20:1, Nollex's picture sums it up; the second anchor sets and lifts the primary out.
  • If the scope is >20:1, as soon as the wind shifts the primary rolls out, because the back tension prevents it from shuffling. It will then remained pinned on its back by pass-through tension.
  • The only time it can help is on rocks and cobbles. But the scope must be 20:1 to prevent lifting, and the only reason it helps is by increasing hooking possibilities. It does not actually make the hold stronger.
I have never seen a picture of an in-line tandem with both anchors set. If you look at the Rocna photos, the anchors are not set and there is no change in correction of pull (even 10 degrees of yawing makes a difference--it does not take a change in the weather).

V-tandems can work, but that is a whole nuth' topic. 98% of the time, one anchor is best.
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Old 25-09-2017, 11:22   #9
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Re: Tandem anchoring

Quote:
Originally Posted by AnglaisInHull View Post
Try a search - there was a long thread on this a couple of weeks ago. To summarize: nobody seems to think it's a good idea, for a number of well-explained reasons.
This "nobody" thinks it works quite well with the method decsribed in Post #43 of the thread you referred to.
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Old 25-09-2017, 12:16   #10
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Re: Tandem anchoring

Sorry, I meant few people think it's a good idea, except in very specific circumstance.
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Old 25-09-2017, 13:06   #11
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Re: Tandem anchoring

When I anchor in heavy currents or swells I sometimes use a 2nd anchor on the same chain. Shackled to the chain about 3 fathoms from the main anchor. The point is to hold the shank of the main anchor down so the boat motion doesn't cause the main anchor to dig itself out. I generally don't anchor in places where wind or current rapidly changes. It's a pia to rig and unrig and the 2nd anchor has to be brought up and manhandled to the deck. Thinking of adding a davit at the bow.
In the old days ships would add a heavy weight like a small cannon to the rode.
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Old 25-09-2017, 13:13   #12
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Re: Tandem anchoring

This debate again . . . . . the folks who say it flat out does not work or is a myth still dont understand how it is actually used in the real world.

Lets start by agreeing. If you have the option to get one anchor (of a good design suited to the particular bottom) which is the combined weight of the proposed tandom . . . the one anchor will win the majority of the time. (as thinwater alluded to) The major exception is on a flatish rock/coral bottom where no anchors are going to actually 'set' but two anchors have more chance of catching on something.

However, that is really not the real world circumstance where randoms are considered/used. Out there we have the anchors we have. We are not running to the store to get a bigger one. So we have let's say 4 anchors on board, and we have a forecast for hurricane force winds. The practical question is then how best to deploy the assets you have. I personally have found (and see on other boats) some value in the tandom concept in two particular circumstances. One is when you are shore tied or med moored, especially in a narrowish harbour (like in Chile). In that case, I would sometimes put my best all chain rode all out plus some rope (so like 400' of rode when I am in only like 15' of water) with tandoms on the end with a good distance (perhaps 50' of chain) between the tandoms. You are hopefully shore tied against the direction of the strongest wind but if the low might go north of you, this might save the boat. In the other case, in say a pretty big Labradorean or Iceland harbor, with bald land and essentially zero wind protection and no shore tie possibilities, I would choose to put my 4 anchors out on two tandom rodes, again with huge (as big as possible scope) in a V against the forecast wind direction.

In both those situations I found the tandoms better than the alternative which is to put out the multiple anchors on separate rodes. My experience with that was you often pull on one and then the other and almost never get a balanced pull on them both.

The other thing to realize is that the wind is very very infrequently steady/constant. It usually has significant variation, gusts and lulls, so theory or tests using a steady load/pull are not really a very good indication of actual effect. The variation tends to favor the tandom over the alternative, giving the two anchors more opportunity to engage. A tandom is never going to be worse than the furthermost out anchor, at the very very worst the closer anchor will act as a high drag chum. (edit: all this does assume it is done in the correct way).

Again, none of this is as good as the even/ever bigger single anchor (and yes, several of our anchors were quite sizable) . . . . but that is not the question. The question is what to do with the anchors you actually have on board when the forecast comes thru.
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Old 26-09-2017, 00:57   #13
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Re: Tandem anchoring

Some discussion here..

Two to Tandem: Maximizing Holding Power by Tandem Anchoring
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