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Old 16-05-2015, 13:32   #16
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Re: How do you run two anchors?

Tho I have never tried it I have read several articles about using both anchors for a storm setting. First is deployed and that rode is connected to the second anchor and the second deployed and that rode connected to the boat. You end up with one real long rode with two anchors inline. Next time im anchored for a hurricane I'll try it. But I normally get hauled out but you never know.

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Old 16-05-2015, 14:15   #17
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Re: How do you run two anchors?

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Tho I have never tried it I have read several articles about using both anchors for a storm setting. First is deployed and that rode is connected to the second anchor and the second deployed and that rode connected to the boat. You end up with one real long rode with two anchors inline. Next time im anchored for a hurricane I'll try it. But I normally get hauled out but you never know.

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How 2 avoid tangles with 2 anchors on 2 rodes? While there are many ways to deploy 2 anchors, the trick to avoiding tangles if the boat spins is to terminated the second rode to the primary rode about 4-6 feet below the bow roller, and bring only ONE rode on to the boat. If the boat spins, the single rode can absorb that without tangles. Not theory, I have done this many dozens of times without incident.

Two anchors on one rode. I've started a long testing program with Practical Sailor, and I call BS on this method.
  • If the pull is straight line, yes, it can be very strong, even stronger than the individual total. Irrelevant, since the wind shifts. the Navy does this to build 6-8-point moorings.
  • Setting both anchors is nearly impossible unless the secondary is smaller. Remember, the Navy sets these with work crew and divers; totally different. But let us assume you succeeded (but you won't be able to tell in most cases).
  • The scope needs to be double (Peter's data and simple mechanics). For storm conditions, that means at least 20:1. Good luck. If the scope is any less, the pull of the secondary will lift he primary right out of the bottom. I've seen that many times. And remember, the primary was the larger anchor, so you have now reduced the power.
  • Chain won't matter that much. In all of our the testing the chain is off the bottom well before the load is critical. If the chain is still on the bottom, you wouldn't have dragged with one anchor. In deep water it could help, but that 20:1 scope thing is going to be a bugger (25' x 20 = 500 feet = 1000 foot swing circle). Some circumstances, sure.
  • If the wind shifts, the secondary will ALWAYS weaken the primary. Around 45 degrees--a small shift, considering many boats yaw that far--it is virtually certain that the primary will roll-out and be pinned on it's back by secondary rode tension. If you don't think so, tests this to near break out load and take pictures.
I welcome any data that shows a single rode tandem working through a 45-60 degree wind shift. I've run many tests, and they are virtually 100% failures. I really wanted it to work... but it didn't.
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Old 16-05-2015, 14:44   #18
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Re: How do you run two anchors?

^^ as an aside . . . . Where tandems are actually/practically most commonly use are in Patagonia (for shore ties) and med moor's . . . . In both cases, the load is in fact in-line.

It's also a situation where you Can put a huge setting force on the rode (by cranking on the shore lines).
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Old 16-05-2015, 16:52   #19
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Re: How do you run two anchors?

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Originally Posted by estarzinger View Post
^^ as an aside . . . . Where tandems are actually/practically most commonly use are in Patagonia (for shore ties) and med moor's . . . . In both cases, the load is in fact in-line.

It's also a situation where you Can put a huge setting force on the rode (by cranking on the shore lines).
Good Points. Straight line.

However, in these cases, is a shallow angle V not perhaps better?

* The perceive weakness of tangles does not exist, because there will be no rotation.

* Both anchors can be set. With a tandem this is never known unless you dive, and even then you may not be able to fix it.

* The anchors can be mismatched. In a tandem they must either be identical or one much smaller. And pivoting fluke anchors can't be used (they do not have tandem holes, and the secondary can NOT be a pivoting fluke anchor, as it will lift the primary out every time).

* The scope must be 20:1. That is going to be a problem in med harbors.


(I've repeated this experiment with Mantus and Delta anchors--the Guardian does not move and the secondary tension lifts the primary anchor out, even if set.)
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Old 16-05-2015, 17:36   #20
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Re: How do you run two anchors?

Well, I went over my edit time limit.

  • Many will not be able to use their highest holding anchor (Fortress).
(Same experiment as before, but this time it is a very capable Mantus anchor that the Guardian has lifted from a good set (note that I added a low tandem hole, per Rocna--it won't matter that much in this test). As Peter Smith explained, both anchors must have the same drag characteristics. The secondary should be smaller and drag more easily, so basically, you don't gain much. And even if the Primary did stay in the ground, the rules of mechanics and deformable bodies dictate that it will not be carrying any significant load, because the pivoting fluke anchor is "stiffer.")

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Old 16-05-2015, 17:39   #21
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Re: How do you run two anchors?

I do not have any empirical evidence to know which is "better", just know that tandems are used and work well in those two specific situations.

In these stern tie situations you do tend to put out a whole lot of scope, at least as normally calculated, because you tend to end up close to shore in relatively shallow water. Med mooring I guess I would say 15:1 (150' out in 10') was very common and 20:1 usually achievable if you wanted. . . . And in chile usually you can lay out all 300' if you wanted, but we usually only did if we misjudged the distance to shore.

In med moors I know there is a concern with 'V's' about crossing rodes with the next door boats.

Otherwise we rarely used tandoms, because we had big enough main anchors. But another situation we did very occasionally use them was when we got hurricane wind forecasts and wanted to put out all four our anchors . . . We then deployed them in two tandoms in a V, the stronger pair pointed at the expected wind shift. And a final situation we used them in once, on a bottom that had no holding at all (flat concrete like bottom in which no anchor would penetrate) we put a tandom out hoping just the weight and friction would hold, and it did at least upto 30kts.

I will add that the Antarctic charter fleet used them commonly and successfully in exactly the situation you are saying they will not work (which I believe is why Peter ultimately put the tandom hole in his design) . . . . But I don't have first hand experience with that use, nor with your tests, so I can't offer an explanation for the inconsistency. But if I had to guess, I would suggest looking at dynamic vs static effects.
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Old 16-05-2015, 18:26   #22
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Re: How do you run two anchors?

I used 2 danforths in train as a semi-permanent mooring in NZ many years ago - I was using one anchor which picked up a rock square in its mouth and started wandering towards the seawall one night - then the bloody tide changed and the rode slipped down and jammed on the mid hull sealog fitting leaving the boat beam on to the current. So I put another anchor on the same line and it never dragged again. I tried it recently with an all chain rode and twisting was a problem so its not something I'd recommend on a short term use basis, but if you need a bit of extra security and dont mind the time to get it set properly, its quite effective.
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Old 16-05-2015, 18:58   #23
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Re: How do you run two anchors?

I sometimes put out two anchors...in a vee from the bow. This stops all "tacking" and really holds the boat in place. Also, decreases the force on either anchor. It really works. But, often wake to a tangled mess in the morning if it goes calm overnight.

Once at Main Duck Island (Lake Ontario), I was anchored near shore (offshore breeze). I was worried the wind would go light and I might end up in the shallows. So I let out all my rode, dropped a second anchor over the stern, then took up half the rode again. During the night the wind switched 180, onshore, and started blowing hard. That stern anchor held me secure, while other boats woke in the night to move. If I hadn't set that second anchor, I might have been on the rocks. In the morning, I brought up the first anchor, then moved the stern rode to the bow. By then the anchorage was very rough, so up anchor and got outta there. A few minutes out, my engine quit. If that had happened during the night, I might have been in real trouble. As it was, I made sail and got home safely, although breakfast was mighty late.
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Old 16-05-2015, 19:06   #24
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Re: How do you run two anchors?

Mestrebe

I wish I'd had someone lik you explain the Bahamian Moore before I anchored in the Cohancy river off the Delaware bay. That setup would hav kept us off the hard (mud and grasses ) and made for a much better night.

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Old 16-05-2015, 20:30   #25
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Re: How do you run two anchors?

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Originally Posted by estarzinger View Post
I do not have any empirical evidence to know which is "better", just know that tandems are used and work well in those two specific situations.

In these stern tie situations you do tend to put out a whole lot of scope, at least as normally calculated, because you tend to end up close to shore in relatively shallow water. Med mooring I guess I would say 15:1 (150' out in 10') was very common and 20:1 usually achievable if you wanted. . . . And in chile usually you can lay out all 300' if you wanted, but we usually only did if we misjudged the distance to shore.

In med moors I know there is a concern with 'V's' about crossing rodes with the next door boats.

Otherwise we rarely used tandoms, because we had big enough main anchors. But another situation we did very occasionally use them was when we got hurricane wind forecasts and wanted to put out all four our anchors . . . We then deployed them in two tandoms in a V, the stronger pair pointed at the expected wind shift. And a final situation we used them in once, on a bottom that had no holding at all (flat concrete like bottom in which no anchor would penetrate) we put a tandom out hoping just the weight and friction would hold, and it did at least upto 30kts.

I will add that the Antarctic charter fleet used them commonly and successfully in exactly the situation you are saying they will not work (which I believe is why Peter ultimately put the tandom hole in his design) . . . . But I don't have first hand experience with that use, nor with your tests, so I can't offer an explanation for the inconsistency. But if I had to guess, I would suggest looking at dynamic vs static effects.
Good points. However, like your knot-testing, without data we are never sure what "it works" means. We don't know that a single anchor would not have done as well, since it is a pass/fail test with very limited observation.

I certainly see the point in a med moor (no crossing lines) and when placing 4 anchors (each line will see a straight pull); the math works and I would do the same. The benefit will be slight, but what the heck.

The dynamic effects point is well taken. That is going to take a lot of play to reproduce.

* On line of reason is that there is some circumstance where the secondary allow the primary time to reset, but I very much doubt that on sand or mud; in every test the secondary only makes re-set less probable, which is scary. For every case where it helps, there are 5 where it hurts. I can prove that. The fact that only Rocna includes a tandem hole and that most manufacturers advise against single-line tandem rigs suggest that there are substantial negatives. Spade has tested and is adamant, and they make a right good hook.

* More likely, on irregular rocky or coral bottoms, the benefit is that one of the anchors will catch, and if there is dragging on a shift, there is a better chance of one of the anchors catching on a rock as the chain pivots around (they will tend to sweep a swath of bottom). I am completely willing to accept this probability, though it does not apply to sand or mud; sand and rock anchoring have almost nothing in common--even discussing them together is dubious. I can also easily imagine that 2 rodes dragging around on a rocky bottom is a rat's nest waiting to happen; something will hang-up.

I should have said up-front that I do believe that certain bottoms may favor a single line, but they will be irregular bottoms. A completely different case, commonplace in some areas, non-existent in others. But this deserves investigation as it makes sense.

I really hoped to see a single line work in sand and mud--I would have like to use the method some days--but the evidence, logic, and industry opinion against is quite strong for sand and mud. Rock is completely different; trouble is I don't have a good test bottom available to me (all sand and mud here).
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Old 17-05-2015, 07:30   #26
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Re: How do you run two anchors?

Agree with all you say.

Like with most anchor things it's hard to be sure.

The Bruce design sucks in every test but a few of us have better luck with it than a rocna . . . Difficult to explain but a real world truth.

There are apparently tandoms used in deep rig drilling. I don't know in what specific situations.

The Antarctic guys clearly know about and have tried V solution. We can't just say they are ignorant or stupid.

As you and Peter point out, there are very clearly engineering weaknesses to the tandom set-up.

All in all, the most practical answer is to avoid the whole issue by getting a 'big enough" main anchor . . . But there are still extreme situations when you want to "put it all out" and right now it's not real clear (to me) the best way to do that in different situations.
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Old 17-05-2015, 08:08   #27
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Re: How do you run two anchors?

> In med moors I know there is a concern with 'V's' about crossing rodes with the next door boats.

In med moors there is a concern with crossing rodes, period. With two anchors in V it's a certainty: your neighbours won't like you.
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Old 17-05-2015, 12:12   #28
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Re: How do you run two anchors?

Starzinger:

Bruce seems more able to do something when dragging on its side at short scope than any other design. That is all I can guess.

I've worked around deep water anchors just a little; they are carefully lowered into place, butter side down, and never see a side pull. A different fish.

I would love to know what bottoms the Artic guys are working with; I bet that is the answer.

Red Herring:

The med moor thing is certainly true. Only I will never see one in the US. Or at least not yet. So it is not a part of my reality or personal selfish interest. That same is sort of true of rocky bottoms; not in my small world.

----

But the Med moor is outside my first post; it does not include wind shift, so I never argued against it. That is why single line tandems also work for Navy and oil moorings; no direction change.
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Old 17-05-2015, 15:08   #29
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Re: How do you run two anchors?

^^ Antarctic bottoms are ground up rock . . . . In some places very finely ground = thick mud, in others medium ground = gravel, and in others course ground = large stones. Often the "mud" is very stiff to completely frozen. The thickness of this ground layer varies (from very thin an inch or two to quite deep a meter or two) but is then most always over a pretty smooth solid sheet of rock. And there is often some thick kelp.

It's about as different from Chesapeake bottom as you can get.
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Old 17-05-2015, 15:31   #30
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Re: How do you run two anchors?

2 anchors on the bow on rollers ready to deploy. 1 Danforth and 1 plow, so we can quickly switch if one isn't holding. We also keep a 3rd in the aft hatch on an all rope rode.


The vast majority of the time, we use a single anchor but there are a couple situations where we will use two anchors:
- Occasionally in shallow anchorages daytime only (not leaving the boat), we will use a stern anchor to hold the bow into the waves. This is typically in shallow water when we are swimming, so we just walk the anchor out and set it by hand.
- With reversing currents, we will do a Bahamian Moor with the two bow anchors. Set the upstream anchor and then let out twice what it needs and drop the second anchor, then adjust the rodes so you are in the middle. We do pull the boards and rudders up so they don't hang up on the anchor lines. We normally don't stay in a spot more than a day or two, so twisting isn't a big issue. For longer term, it would be problematic but we've seen people motoring in circles to untwist them.


Unlike some, we love the options provided by multiple anchors all ready to deploy.
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