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Old 19-01-2013, 07:06   #16
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Re: Tandom anchor...two anchor system

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Originally Posted by RabidRabbit View Post
Yea thats not what happens when their set, you just pivot around the heavest mid rode anchor. Your just spreading fear cause its not the way you like to do it. Standard operating procedure here at CF, the old crowd set in their way telling the newbie young guys, theres only 1 way to do things. OMG I am so sick of hearing that wind & current will, tangle a rode, pop an anchor out, ect.. Wind & current are everywhere, at least where I anchor, changing directions 180 is anchoring, not some freak occurance in a bad anchorage.
If the wind or current is calm and it shifts around with one anchor it will tangle some times.

This two anchor setup only compounds the problem. Chain anchor ball tangles are no good as they can reck your good night sleep.

The current one anchor solution has been working well for hundreds of years.
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Old 19-01-2013, 07:17   #17
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Re: Tandom anchor...two anchor system

I think the system has some merit. Particularly for weekend fairweather boating.

A couple of points...

Judgement on the weight of anchors may be a little harsh because we've got no idea what size boat they're using.
They look like Rocna-style anchors so should always roll over and dig in and some think you can use lighter anchors if using newer designs.

Jolly Roger, a member here, personal friend and very experienced cruiser always tandom anchors and has had occassions when a couple of dragging boats have hooked up as they're going by and his ground tackle held the lot of them. But he does use big anchors.
His method is to pay out his primary, hook the secondary with a short chain to the primary rode once some has been payed out. Then 5 times scope. He has never dragged with this setup.

Having said that, I've just made the 65lb cqr the boat came with the secondary, and now have a 105lb cqr as the primary. I will now feel ok about using one anchor unless conditions call for the secondary too.

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Old 19-01-2013, 07:22   #18
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Re: Tandom anchor...two anchor system

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There's only 1 rode, whats going to get tangled? and for scope, I measure scope from the 2nd anchor, not the one on the bitter end of the rode, so why would it be doubled?
I like that people try new things. Really.

Why double rode? The engineering has been evaluated many times. When the load comes on enough to straighten the chain one of 2 things happens:

From and angle. The closest anchor is lifted rolled on its side and cannot reset because the rode tension keeps it on its side. This requires a look a the force vectors, but even in the video you can the anchor loosen before it should. Experiment with this on the beach. It cannot reset until the second anchor drags, so you have not increased holding power much.

Straight load at 2x single anchor load. The second anchor basically converts the first anchor into an over priced kellet. If the second (tip) anchor is smaller (generally the case) you have actually weakened the anchorage.
Two to Tandem: Maximizing Holding Power by Tandem Anchoring
You may not like the product, but his math and writhing are clear.

I can see that it gives peace of mind, and there is always some who will say something saved them (but they may not have dragged anyway), but in this case the math doesn't seem to work. The only real advantage may be double the odds that the anchor can find a good bottom. Sometimes that may be worthwhile. I think I would prefer to dive on the anchor before a real storm, no matter how cold the water; I've got a wet suit and I've gone in cold water many times.
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Old 19-01-2013, 07:28   #19
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Re: Tandom anchor...two anchor system

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The V system with 2 rodes or bahamian moor is way old school, outdated and not that many people use it anymore. All sorts of 30-50 year old books explain it and it keeps the myth alive. It this thread tangled rodes has been mentioned, but did anyone watch the vid? There's only 1 rode, whats going to get tangled? and for scope, I measure scope from the 2nd anchor, not the one on the bitter end of the rode, so why would it be doubled? Dont get me wrong that anchor in the vid looks weak and cheesey, buy the concept of straight line tandem anchoring is very easy, and it beats two twisted up bow rodes.
Actually in the correct Bahamian anchoring technique the anchors are not in a V off the bow but 180 degrees but still both off the bow. This technique was developed to deal with a common problem in parts of the Bahamas were many anchorages are in a cut between two islands along the edge of the banks where you will experience a strong current that reverses direction 180 degrees every 6 hours.

The technique addresses two problems, one the potential for an anchor to not reset or the rode fouling on the shank when the current reverses and second, to limit the swinging room required by the boat since some of these spots are fairly small or crowded.

Still a very useful technique in the right circumstances, especially when all the boats around you are doing the same.
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Old 19-01-2013, 07:42   #20
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Re: Tandom anchor...two anchor system

And, the V system off the bow in big blows also works. I have used the V and the Bahamian moor numerous times.
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Old 19-01-2013, 07:46   #21
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Re: Tandom anchor...two anchor system

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And, the V system off the bow in big blows also works. I have used the V and the Bahamian moor numerous times.
Yep. Bottom line is you use the right tool for the job. No one method or techniqure (or anchor for that matter) is the best for every anchorage or every situation.
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Old 19-01-2013, 07:57   #22
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Re: Tandom anchor...two anchor system

Am I correct you want me to double rode length the when I'm allready at 8:1 ? This 8:1 is before I slap on 50' more chain and the secondary 44# anchor. So I'm always at 8:1 before the secondary anchor or the additional 50'. My point is I'm anchoring properly with a huge anchor(66#) and all chain (better than some here), and yet some here feel that the additional anchor and 50' chain somehow put me at disadvantage, and I'm trying to compensate for lousy anchoring. Maybe read this stuff before argueing how wrong I am.
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Old 19-01-2013, 08:35   #23
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Re: Tandom anchor...two anchor system

With a wing keel, I have given up on the Bahamian moor years ago. We could never find the right set to avoid snagging the keel on a reversing current and creating a potentially dangerous situation if you had to leave quickly from the anchorage. We always set one hook with proper scope and have not had a problem in tidal anchorages. We do, however, try to anchor at the outer edge of the current, if possible, and rarely anchor close to other boats unless absolutely necessary. As others have mentioned, I do see a potential problem with this tandem set up as it unnecessarily complicates anchoring but if it works for you, fine. The bottom line is a good anchor, adequate chain and sufficient scope. That seems to be a constant.
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Old 19-01-2013, 09:04   #24
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Re: Tandom anchor...two anchor system

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With a wing keel, I have given up on the Bahamian moor years ago. We could never find the right set to avoid snagging the keel on a reversing current and creating a potentially dangerous situation if you had to leave quickly from the anchorage.
Not as bad a problem but certainly a concern even with a non winged keel.

After much trial and error I decided the secret is to leave a good bit of slack in the anchor rode that is set behind the boat so that rode is actually hanging down from the bow and lays on the bottom under the keel. Then when the current reverses there is enough slack for the rode on the bow to drop to the bottom, the boat and keel drifts over that rode until it takes up the slack on the other rode.

That seemed to solve the problem of snagging on the keel for me. Still had a problem with the rodes tangling after sitting for several days going in circles every six hours. After a week or so you can end up with a real mess. I got to the point that if I was staying in a reversing anchorage for a while I would remove one of the rodes every couple of days, unweave the macrame and recleat.
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Old 19-01-2013, 09:07   #25
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Re: Tandom anchor...two anchor system

In a Bahamian moor put out the second anchor on mostly rope rode and keep the extra rode in a sailbag. Once or twice a day pass the sailbag and line around the other rode to keep them from getting wound up. Takes five or ten minutes at the most each day to keep from having a tangle.
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Old 19-01-2013, 09:57   #26
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Re: Tandom anchor...two anchor system

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In a Bahamian moor put out the second anchor on mostly rope rode and keep the extra rode in a sailbag. Once or twice a day pass the sailbag and line around the other rode to keep them from getting wound up. Takes five or ten minutes at the most each day to keep from having a tangle.
Pretty much what I would do but it was a bit of a hassle for a couple of reasons. My second anchor was mostly rope but 250' and in the Bahamas was usually anchored in 10' or less so had a lot of extra rode on deck making a fairly large, awkward and heavy bag to wind around the other rode.

Also I'm a bit paranoid about losing the anchor so insist on keeping the bitter end always attached in the anchor locker so would have to climb in to undo that as well. Minor however compared to swinging 150-200' coil of rope around the bow.

So yea, it is doable but I always had to whine and complain a bit. Guess I'm just too easily annoyed.
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Old 19-01-2013, 10:04   #27
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Re: Tandom anchor...two anchor system

"So yea, it is doable but I always had to whine and complain a bit. Guess I'm just too easily annoyed." Skipmac


Exactly!
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Old 19-01-2013, 10:31   #28
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Re: Tandom anchor...two anchor system

very ingenious. The big advantage to having two anchors, at least in my mind, would be if they were set 180 degrees apart for wind shifts. this scheme doesnt do that, and risks tangles and complication. I dont get the point I guess. Wind shifts are the big reason for anchors coming loose.
What the world needs is a siamese anchor, with a sliding attachment and 180 degree double shank. basically two anchors joined butt to butt. Of course you stow the damn thing!
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Old 19-01-2013, 10:44   #29
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Re: Tandom anchor...two anchor system

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Am I correct you want me to double rode length the when I'm allready at 8:1 ? This 8:1 is before I slap on 50' more chain and the secondary 44# anchor. So I'm always at 8:1 before the secondary anchor or the additional 50'. My point is I'm anchoring properly with a huge anchor(66#) and all chain (better than some here), and yet some here feel that the additional anchor and 50' chain somehow put me at disadvantage, and I'm trying to compensate for lousy anchoring. Maybe read this stuff before argueing how wrong I am.
If you found a specific error with Peter Smith's math, please explain it.

Yes, I read. Please read Peter's entire post; it is long and very thoughtfull. No, I am not being argumentative. Engineers rely on both math and actual practice, so I am interested in threads like this.

Have you ever played tug or war? Imagine tug of war where the rope is pulled both up and to one side.
  • IF the biggest guy is near the front, his efforts are diminished as he is pulled off his feet. The angle needs to be very low to prevent this. Yes, 8:1 rode is probably not enough, only equivalent to 4:1 when there is a second anchor.
  • IF the biggest guy is in the back, the first guy is irrelevant. We all know this.
  • IF the rope is at an angle (and it always will be after 30 minutes) only the first guy is relevant. There is no load on the second anchor.
The only time tandem anchoring makes good sense, in my interpretation, is when the bottom is such soft silt you expect things to move around, or bottoms that are inconsistent and a good set is impossible (mud over super hard clay). Then, the more iron of the bottom, the better, including using a LOT of scope.



---


These are not my engineering arguments; Peter makes them well and I can find no logical flaws. At first glance they might seem counter intuitive, but so is much of sailing and engineering.
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Old 19-01-2013, 11:39   #30
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Re: Tandom anchor...two anchor system

Boy this is like flogging a dead horse, I am well aware of Pete's writing. I think we are misunderstanding our 1st and 2nd anchor positions (a whos of first sorta thing) If your taking from this that I ever have 4:1 scope your not understanding me. Good ole pete is the guy who set on this tandum anchor path. Pretty sure he points out that after 8:1 scope it gets pointless and hard to change the angle of attack. Let me say again that my scope is from bow to bigger anchor 8:1, then if running tandum the additional chain (50') and anchor are shackled to the bitter end of the larger anchor not the end on deck or even anywhere on my primary chain. How is this 4:1? Its not, What I dont understand is why you feel this need to be so right, clearly making me wrong.
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