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  #11  
Old 07-24-2003
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Slipping at Anchor

Jeff_H
I have read about this tandem arrangement you mention several times, but have always wondered about how you go about setting such a setup. Seems to me that when you back down on it, one of those anchors is going to set first, and then keep the other one from setting. If it''s the one at the end, not so bad, but if it''s the one 40 ft. in ( i think this one is usually smaller than the other), you would be hanging only on that smaller anchor.
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  #12  
Old 07-25-2003
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Slipping at Anchor

I often set 2 (or more) separate anchors at 30 - 60 degrees. This would split the load when set (@ that loading angle), provide some protection against wind shift, and be easier to set, re-set, and retrieve (than 2 tandem hooks). See also previous ''Yodagab'' posting.
Notwithstanding, it would not provide quite as much holding power against the exact angle of initial wind as (2) well-set tandem anchors. I use a kellet as a kellet (sentinel weight), rather than an anchor.
More importantly, I carry anchors EACH designed to hold my boat in wind/current/wave conditions to 40 knots - and I ''look'' or ''dive'' them prior to cocktails. No anchor will hold if not properly set!
As previously noted, I use the Bahamian Moor in tidal situations.
With one notable exception (I''ll tell the story sometime soon), I''ve never dragged - even in hurricane conditions.

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  #13  
Old 07-25-2003
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Slipping at Anchor

Hi Gordon,

A couple quick counter points. I think that tandem anchors are actually easier to retrieve that multiple anchors set in a vee. When you use separate anchors on separate rodes it is not unusual to have the rodes that twist around each other and become a pain to retreive where as with tandem anchors you are simply recovering a single rode. The other issue with putting anchors out at 30 to 60 degrees is that as the wind switches about you are left hanging on one then the other. At best at those times this is no better than a single anchor and at worse the anchors creep in toward each other and one anchor can capsize the other. While I have not checked the math, I have generally heard that because of the geometry of the pull, when both anchors are loaded equally, the load on each anchor can actually exceed the load that would have been experienced by a single anchor alone. (With a 60 degree spread, the load in the downwind direction equals the shorter vertical leg of a triangle while the anchor rode experiences the component of the load diagram that is the hypotenuse.)

Jeff
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  #14  
Old 07-26-2003
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Slipping at Anchor

Multiple anchors & rodes:

BAHAMIAN MOOR2 anchors from bow @ 170 degrees)
Set and left through wind or tide changes will often end up twisted ''round one another.
Sometimes you are lucky enough to anticipate the direction of (180 degree) rotation, and avoid the twist.
This is pretty much the choice for reversing circumstances, so we end up "dealing /w twist".
I keep the bitter ends of my rodes in a bucket. After each reversal, and subsequent twist, I simply let go the slack rode, and (using the bucket) untwist it round the loaded road, then re-fasten.

2 ANCHORS on 60 DEGREE "V".
Mostly used to anticipate smaller wind-shifts < 90 degrees).
Seldom had problems /w twisting.

Jeff_H makes the points:

That a single rode (with 2 anchors "in-line") can be easier to retrieve than 2 separate rode/anchors. I agree that the process may be simpler (a single action), but suggest that there is a potential problem /w short-scope after the nearest anchor is up, and you''re still retreiving the outer anchor (about 40'' away). At that point, you may have interrupted your retrieval to deal with the "dry" anchor. Mostly no big deal, but one consideration in an "escape the anchorage" situation. The "V" option allows me to retreive the slack anchor, then deal with the loaded anchor in one continuous operation - or even "float" and temporarilly abandon it (with the first anchor aboard).

Jeff also notes that, as the wind moves, you will be left hanging on only one of the 2 anchors. This is true - the "V" only splits the load (more or less equally) between them as long as the wind bisects the angle of set.
My intention, in setting the "V" is not to split the load, but to increase the chances of having a more "in-line" pull under shifting winds.

BTW: I think you may have heard that the whole load is greater than the sum of the loads, not that each load is greater than would be a single. Neither, do I belive this true - the whole is equal to the sum, as long as both are loaded. I''d like to see that math''s, otherwise.

Finally, I''d like to return to my original premise that EACH anchor (in a multiple set) must be able to carry the anticipated load.

Due to the wide variety of anchoring conditions we may encounter, and equipment available; the well-prepared seaman should have several tactics available to him/her for any given situation. Discussions, such as these, provide the variety of experience and opinion that can help decide the best/better tactics in a variety of specifics.

I suggest a Hegelian Dialect (Thesis + Antithethis = Synthesis) approach to this dialog helps provide us each with a great store of knowledge upon which to draw. Very useful, indeed.

More opinion???

Regards,
Gord May
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Old 07-29-2003
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Slipping at Anchor

The math on this is something I do understand: The only way to get the pull on the anchors to exceed the pull on one anchor alone would be it they are both loaded equally and they are set over 120 degrees apart. Since the boat can move, there is only one point at which this can happen, otherwise one of the "legs" of the triangle is too long, and it goes slack. Line strech in the rode will make this a little less precise, but not by much.
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  #16  
Old 07-30-2003
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Slipping at Anchor

To THERMAL et al:
Does your understanding of the Math lead to any conclusions regarding the efficacy of the (3) discussed anchoring strategies? (Daisy Chain 2 Anchors on 1 Rode, 2 Anchors “V’d” on 2 Rodes, or Bahamian Mooring /w 2 anchors at 120-180 degrees)

The purpose of the “V’d” anchors, as I use them, is primarily to prepare the set-up for moderate wind direction changes - not to “split” the load. Because the wind seldom bisects the angle, I expect the boat to lay to 1 anchor, whilst the other rode is slack.

Likewise, I use the Bahamian Mooring to anticipate 180 degree load changes (usually tidal).

Hence, I don’t believe that the inability (of multiple anchors on separate multiple rodes) to effectively “split” the load, is detrimental to my intended purpose.

My previous comments on the “Daisy Chain” of 2 anchors on 1 rode should not be understood to be entirely negative. It’s an acceptable back-up alternative to a suitably sized single anchor. I prefer, however, that each (properly set) anchor should be able to do it’s intended job - ON IT’s OWN.

The most important element in achieving a safe anchorage is effectively setting the anchor, followed (in no particular order) by anchor size & type, and anchor placement. No strategy will work, until & unless the anchor is set.

OMO
Regards,
Gord May
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Old 07-30-2003
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Slipping at Anchor

Gord correctly states that having the anchor(s) truly set is critical. On our recent charter in the BVIs, I found two occasions where the anchor would apparently hold while backing down at half reverse thrust, but would drag at full reverse.

It took a long time on one of those occasions (about 1.5 hours) before my wife suggested we take a mooring ball, so we never did get to set an anchor there during that visit. The anchor was a fairly large Bruce with 100 feet of heavy chain, and the depth there was only 10 feet.

I witnessed others having similar problems, although they all eventually lay to their anchors since we grabbed the last mooring ball. I could not help taking the dink over to discuss this frustrating situation, and learned that they, too, would drag if they went to full reverse. They decided, based upon predictions of good weather, that they were OK, however.

So, to my question: Isn''t it true that your anchor should be able to resist your sailboat''s boats full reverse thrust? I believe if it cannot, then the anchor is not set (or the holding is just inadequate, like soft mud, etc.)

What say ye?

Duane
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  #18  
Old 07-30-2003
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Slipping at Anchor

Full reverse thrust, on most sailboats, simulates a wind speed of (only) about 20 Kts.
Absolutely, the anchor must resist full reverse thrust and more!!!
Gord
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Old 07-30-2003
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Slipping at Anchor

Duanne, I believe we were in the BVI during the same period of time as you.

Anyway, one Saturday night in the middle of July we anchored at Cooper Island during benign conditions. I dived the anchor and it was very well set and deeply dug into the sand in spite of surrounding grass. I had about 70 ft of chain out and was anchored in about 10 feet.

We anchored at about 15h00 and all was well until 03h45 when we awake to the sound of the most horrific squall yet encountered. the wind came from the direction of the snorkeling rocks (west) which was a big shock.

In driving rain and winds at more than gale force I quickly realized we were dragging and dragging onto other boats on moorings. I could see people everywhere checking their mooring balls and could hear them thinking they were glad they weren''t the fool who anchored...

We ended up having to pick up our anchor (it took significant engine revolutions to drive into the squall). We carefully exited the mooring field in pitch black darkness into the open area just beyond and continued to drive into the storm.

30 min later all was over and we could pick up a mooring.

We did not anchor at Cooper Island again...

Magnus Murphy
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Old 07-31-2003
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Slipping at Anchor

Magnus,

Yes, we were there at the same time. Thanks for sharing your Cooper story. I have only used a mooring ball there; never anchored. I understand a SunSail boat was severely damaged a few weeks ago when a mooring broke in high winds at night.

You may have read our 8-18 Jul report with our story of losing the engine and having to anchor at dusk under sail in a not-so-protected spot in Trellis Bay.

Regards,
Duane

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