Setting and Use of Tandem Anchors

[Kings Gambit]

I just finished reading an article in Sail magazine's "Special Anniversary Issue" on the use of tandem anchors. I guess it's worked for the authors, reporting to have ridden out a Category III hurricane at 110 kts for 12 hr. However, I can't say I learned much more than I knew already about tandem anchor deployments, which is practically nothing!! Regarding theory however: if two anchors are deployed (in tandem) on a single, common, rode the "second" lies about 20 - 30 feet in front of the "primary" (i.e., the one closer to the boat and the larger of the two if of different sizes) to which it is attached, preferrably with chain. Holding power is theoretically increased because the second gets a deeper [than normal] set as it moves over bottom loosened up by the primary as it sets. Can this possibly be true? In the end, both anchors will set as deep as they can--no?

I never saw it that way. I have believed that the second anchor serves principally to keep the primary from pulling out due to its attachment at a zero angle of pull to the primary, and that is how "holding power" is increased. The authors go on to say that holdling power of the tandem array is increased much more in mud than in sand, relative to two anchors deployed separately [each on its own rode].

Also, I'm now a little confused what the authors meant by "holding power." If the anchor(s) pull out; you've lost holding power for sure. But, what if you're dragging with anchors partially in? It would be harder to drag two anchors held together in tandem through mud than one at a time (e.g., two anchors deployed on separate rodes); so that increases "holding power" for the tandem array, but if you're dragging--IMHO--you're not "holding." That the relative holding power difference in sand is much less than for mud suggests that anchors set in sand on proper scope are much less likely to pull out to begin with; so the second anchor in the tandem array is not doing that much. To me, that says the job of the second anchor is to keep the primary from pulling out and has NOTHING to do with the notion of a "deeper" set initially. Does anyone here know?

 

[Stu Jackson]

KG, that article also appeared in Cruising World some years ago. I thought, at first, that it was a very good idea. Then i did some reading. IIRC, Evans Starzinger did a response to that article in which he detailed the many reasons why it was NOT such a good idea. A Google search would most likely find it, and Beth and Evans have their own website, too, it may be there. http://bethandevans.com/

 

[Kings Gambit]

KG, that article also appeared in Cruising World some years ago. I thought, at first, that it was a very good idea. Then i did some reading. IIRC, Evans Starzinger did a response to that article in which he detailed the many reasons why it was NOT such a good idea. A Google search would most likely find it, and Beth and Evans have their own website, too, it may be there. http://bethandevans.com/

OK--thanks; I'll have a look; but my question is more about how the tandem array "increases holding power" (if it does).

 

[Kings Gambit]

KG, that article also appeared in Cruising World some years ago. I thought, at first, that it was a very good idea. Then i did some reading. IIRC, Evans Starzinger did a response to that article in which he detailed the many reasons why it was NOT such a good idea. A Google search would most likely find it, and Beth and Evans have their own website, too, it may be there. http://bethandevans.com/

Some interesting reading out there on desirabiliy. Most appear to infer "to be used [tandem anchoring] only as an act of desperation." That's funny. Better to have an oversized storm anchor aboard is the consensus.

 

[Gunni]

OK--thanks; I'll have a look; but my question is more about how the tandem array "increases holding power" (if it does).

The theory is that you have twice as much anchor fluke in the bottom and thereby increased holding power. The problem is you can't really know that you actually have two properly set anchors. I haven't read the Sail story but the notion that a single rode tandem anchor is preferable to a twin, or even three rode set in a hurricane strains credibility.

 

[Ron20324]

The theory is that you have twice as much anchor fluke in the bottom and thereby increased holding power. ... the notion that a single rode tandem anchor is preferable to a twin, or even three rode set in a hurricane strains credibility.

Unless it is just making the point that if you are caught unawares in a storm, and have only one rode, putting two anchors on one rode is better than one on one.

 

[Kings Gambit]

He did not say how many anchors were down; I presume only the one tandem array. The mention of the storm was to gain credibility that it (the array) works if you know how to set it, etc. Apparently, they left an exposed marina to ride that storm on the hook as it was believed to lower the risk of damage to the boat.

 

[Chris Patterson]

Seems to me that the anchor closest to the boat would just be acting as a Kellet. (sic?)

 

[Kings Gambit]

Seems to me that the anchor closest to the boat would just be acting as a Kellet. (sic?)

I don't know; it's the stronger (bigger) anchor.

 

[thinwater]

Your missing the real reason for Sail Mag publishing the article. Advertising. Little gets written for Sail that does not support advertisers.

Weber Marine introduced a really brainless tandem anchor system (the second nests inside the first) and they are an advertiser. I'm willing to bet the secondary would be jammed when you need it, the combination makes a poor primary, it will cost more than 2 good anchors, obviously you have not added weight, you have gained no redundancy, and it can't be used open hawse. Silly, but someone will buy it. Poor devil.

So there is the reason. Everything else in the article was stolen from Peter Smith's excellent article (http://www.petersmith.net.nz/boat-anchors/tandem-anchoring.php) or is anecdotal tripe. IMHO.

 

[Joe]

Bobby Schenk, in his book "Long Distance Cruising" absolutely discredits the tandem anchor technique. His comment was that in his many years of worldwide cruising he had never met anyone who recommended it.. Besides the potential damage to the boat when deploying or retrieving, they are almost impossible to set correctly..

Instead, he and all his cronies highly recommend the deployment of multiple anchors on separate rodes.... making a point that this does not increase holding power per se... but lessens the probability that an anchor will break out when the boat swings. In other words the holding effort switches between anchors and if one fails the other will still be holding.

 

[rgranger]

KG
I also read that article and wondered how I would be able to set both anchors.. and know if I had done so. I also viewed the "primary" anchor as an extreme version of a sentinel.

I can imagine that if the "primary" is jerked out in a surge, the secondary anchor can hold it in place until it resets.

I read a post once (I think it was here) and the OP gave a report after a big storm hit a Marina on the NE coast. He said the only boats that survived are ones that had deployed three anchors in a star pattern. That intuitively makes a lot of sense to me.