The great anchor debate - whats are take

[duncan]

Re: The great anchor debate - the critical missing factor

/forums/images/graemlins/cool.gif well put Craig

glad we are back to agreeing..................

 

[hylass]

Re: The great anchor debate - the critical missing factor

[ QUOTE ]
<span style="color:blue"> I would always have available a " Fisherman" for rock or weed </span>

[/ QUOTE ]

I was once in St Malo bay with a sailing magazine journalist on a big motor boat, doing anchor tests..

After a muddy and a sandy bottom we went to a place well reputed for weed.

The journalist tooks both a Fisherman anchor and a grapnel .. and as I was laughing, he told me that it was the only anchors which worked on weed.

We throw both.. and no one did penetrate and hold.. and the journalist conclusion was that the weed was too dense and that no anchor could work in such a situation..

I had to strongly insist to try one, in fact two different brands, “new generation” anchors and both set immediately and hold..

When publishing the Article, the journalist wrote that the “new generation” anchors are much better for difficult situations such as weed..

[ QUOTE ]
<span style="color:blue"> Tandem anchoring isn't to be advised for normal circumstances. However, it is one way of dealing with extreme conditions. </span>

[/ QUOTE ]

as I was not happy at all with my plough anchor, I did try the tandem set technique.. with no more success..

I personally almost lost my boat trying out this idea. At the time, my first anchor dragged, so I decided to try something new. I added a smaller anchor in front of the large one. This worsened the holding power as opposed to doubling it, drifting swiftly on the smaller anchor while the larger one couldn’t grip at all.

I have done a series of approximately 70 tandem anchorages in the clear waters of the Med, diving on nearly all of them.. in 62% of the cases, only one anchor was set.. During bad weather, you will not have the possibility to dive to check your anchors.. and you only have to “trust” your anchors.. Which is what I call “the Russian Roulette” anchoring..

Therefore attaching two anchors to one rode, known as tandem anchoring, should be avoided.

On an imaginary level, it might seem like two anchors should hold better than one. This is however only true when both anchors can set perfectly. Whatever anchoring technique you use, there’s never a guarantee that both anchors are going to set well. On the contrary, once the first anchor is set in the seafloor, it will hinder the other anchor from setting also.

When an anchor has dragged, a trench formed behind it and this quickly backfilled with loose un-compacted sand. These areas can be still visible after several tides and may explain why some popular anchorages are criss-crossed with patches of poor holding.

Then, if the most proximal anchor set, they are very good chances (?) that the distal anchor will fall down in this loose bottom, with, as a consequence, a poor holding!.


Below, you will also find a letter from Jean Louis GOLDSCHMID (Nautical Center of Glénans) published in N° 114 of Glénans news letter (August 83) (“badly” translated from French)

<< The Tandem set technique it is a very good technique with Fisherman anchors and I personally made some experiment at time when the Glénans’s boats only had this type of anchors on board.

On the other hand,. I began one day to have doubts while seeing tandem set anchored boats dragging.
I thus carried out a series of measurements of traction with a motor boat. Almost all the tests gave the same results: one needed 200 rpm less to drag 2 tandem set anchors (CQR or Fluke anchors) than only one of these anchors alone. I thus checked what occurred, with small anchor on the dry maërl beach of “PEN MARYSE” in the Archipelago of Glénans, pulling by hand.

First problem with the CQR:, it doesn’t have any fixation hole to attach the second anchor (that should have been a sufficient reason for not using this technique), I thus tested the bar, the trip line hole, the elbow of the shank. On these 3 points. the effect is the same one: the articulation plays badly, the plow cannot dig in. Remain the extremity of the shank, but it is not better. Almost each time, the chain comes to obstruct the plow The whole system does hold only on the most distant anchor. If this one is smaller, it holds less than only the large anchor one. I noted too that an anchor holds very badly in the furrow of another.

With the “Fluke” anchors: this is again the same problem of devoted fixation, and it does not have there anything which can be used except sometimes the trip line rings which are usually not strong enough. However, from time to time y obtained results comparable with the holding of only one anchor.

I thus concluded from it, that I had sufficiently poisoned my life by re-installed useless scrap heap to definitively give up the tandem set technique.

[ QUOTE ]
<span style="color:blue"> my experience is that extensive scope results in greater likelihood of dragging, not less. As this is contrary to percieved wisdom I don't expect ready acceptance. </span>

[/ QUOTE ]

Anchor holding increase as the pulling angle decrease, most anchor are designed to hold with a maximum angle of 7°
- Angle is achieved by scope, more the scope less the angle, but with scope of more than 10/1 any additional length of mooring line will only give a very small variation of angle.. therefore a maximum scope of 10/1 is recommended



[ QUOTE ]
<span style="color:blue"> Try anchoring on thin sand on coral and you'll find your anchor pretty useless, in fact any "large fluke area" anchor is disadvantaged, however you might get some purchase with a Bruce or Fisherman. </span>

[/ QUOTE ]

No way.. both Bruce or Fisherman are well known for their poor holding, regardless of the bottom


[ QUOTE ]
<span style="color:blue">how many of you actually set two anchors - either in tandem or in a "V", on separate rodes - and how often? </span>

[/ QUOTE ]

I've been living-aboard during 13 years.. at the beginning, I was using a single CQR. After several anchoring problems, I started to use both a plough and a flat anchor, tandem set.. but this was quite difficult to set and to retrieve.. and I have had anchoring problems too.. until I changed for one of those "new generation" anchor.

Since then, (including in the river mouths of Brazil, where current is changing with tide) I have used two anchors less than half a dozen of times..

 

[wagenaar]

quote:
2) What dictates holding power is simply resistance, which you get from fluke area. Accordingly, anchor size should not really be chosen based purely on weight.
I agree, but one should add, that it is the fluke area bedded within the bottom, and not the fluke area of the anchor.

 

[hylass]

[ QUOTE ]
<span style="color:blue"> Just out of interest, how would we obtain an imported anchor either in the UK (where we are) or in Portugal (where the boat is), other than by wiring a large amount of money to New Foundland?
</span>

[/ QUOTE ]

Don´t make your choice too fast..

.. as you may have, before the next 2007 sailing season, some "new" anchors - made in UK - even more performing and at half the price than "imported" anchors.. /forums/images/graemlins/wink.gif

?????????????????????????????????????????????????????????????????

 

[pelicanpete]

For crowded anchorages and twice the security read this http://www.pelicanpower.com/abacoguide/bahamianmoor.htm

 

[ChrisE]

Bahamian moors are fine providing everybody else is and they do in some of the narrow anchoring channels in the Bahamas but in an open roadsted you are a hostage to fortune as the wind or tide shifts and the rest of the fleet swing into you.

 

[vyv_cox]

Re: Using two anchors

This year, for almost the first time ever, we lay to two anchors with about 60 degrees between them. We were in Cala di Volpe, Sardinia for four nights in August, in winds anything from 20 to 50 knots but almost zero fetch. For two nights and days the boat behaved as normal, lots of veering about the (Delta) anchor and snubbing hard against the warp. We had 20 metres of chain out in only about 2 metres of water, later increased this to 25 metres. Diving on the anchor all appeared to be well but living aboard was not very comfortable.

Just for something to pass the time I decided to try the kedge, a Fortress FX16 on 7 metres of chain plus Anchorplait. I laid it from the tender and hauled in on the warp to more-or-less bisect the angle relative to the wind. We were astonished at how effectively this cut out the motion of the boat and we slept far more comfortably during the next two nights. I dived on both anchors again and both were well dug in. When it became time to leave we struggled to lift the Fortress, even with a vertical pull. I shall definitely use this method again in similar circumstances.

 

[kalessin]

Re: Using two anchors

How interesting - that is almost a replica of our experience except that we had quite a bit of tidal current.

Did you lash the two rodes together below the waterline? If so, how?

 

[jimbaerselman]

Re: Two anchors

The Bahamian moor (I didn't know it was called that) deals with winds above 20kts or so coming from a consistent direction when there is either no current, or a current coming from the same direction as the wind. The moor prevents the boat sailing around its anchor. It therefore reduces the chances of collision between boats on 'opposite anchor tacks' in a crowded anchorage. It should not be used if the current is likely to reverse.

To cope with tidal reversal, you'd set one anchor up tide, and one down tide, lashing the two rodes together. I've described the routine in another thread recently. This also reduces 'sailing' in strong winds, but will, of course, create difficulties with other vessels in the vicinity (if they're on a single rode) when the stream reverses.

In my view, the only reason for attaching two anchors (in tandem?) to one rode would be to use the nearer anchor as a form of chum or kellet - ie, a means of keeping the pull angle close to the ground.

In winds over 25kts or so, double anchor constraints are essential if you're using older or less efficient anchors (CQR, Fisherman, flat anchors) which are more likely to trip (and have to reset themselves) after a big sideways pull.

Of course, another double constraint technique is a line ashore . . .

 

[ChrisE]

Re: Two anchors

I think that we are talking at cross purposes. A Bahamian moor is especially designed for narrow channels with a reversing current and is what you describe in your second paragraph. A bit like a personl version of a mooring buoy.

I think what you are talking about, in the first para, is the deployment of two anchors at 30-60 degrees in a wind rode anchorage when the benefits you talk about will accrue.

FWIW, I agree that deploying two anchors from the same rode is counter productive for modern hull shape although might well work on somethnig like a pilot cutter with a deep forefoot.

 

[scarlett]

Re: Using two anchors

For a season in the Med I have used a 6lb Fortress to help a 30 lb CQR copy but the CQR just became the chum for the Fortress, which dug and held a 32 footer in a six.
Hope this is of interest

 

[craigsmith]

Re: Two anchors

[ QUOTE ]
I think that we are talking at cross purposes. A Bahamian moor is especially designed for narrow channels with a reversing current and is what you describe in your second paragraph. A bit like a personl version of a mooring buoy.

I think what you are talking about, in the first para, is the deployment of two anchors at 30-60 degrees in a wind rode anchorage when the benefits you talk about will accrue.

[/ QUOTE ]It's just semantics but you're both talking about variations of a Bahamian moor.

 

[roly_voya]

Re: The great anchor debate - the critical missing factor

Quote

The boat is very wind-rode and sails freely up to and round her anchor unless it's blowing >F4. A long scope allows her to pick up sufficient speed to yank the anchor up.

From experience this does seem to be a big problem with some boats and if its bad enough is going to defeat almost any anchor. As my boat compleatly ignors the wind and lays to tide the only time I have had this problem is on a river mooring with 3kn tide, kept riding over the bouy. I solved the problem by streaming a droge of the stern which work fine. Have you tried riding sails or setting anchors astern or to the side to prevent her picking up way?

 

[ChrisE]

Re: Two anchors

In one sense you are right both techniques use two anchors but for the avoidance of doubt.

Bahamian moor is placing anchors at 180 degrees up and down tide of tidal channel, where swinging room is at a premium or not possible because of the configuration of the channel. This is a crap method in any kind of cross wind.

T'other is laying a pair of anchors, when a blow is expected, specifically for a wind rode anchorage to add a bit a grab and to prevent sailing around a single anchor.

If you disagree, I suppose you won't mind me calling a Rocna, a Spade /forums/images/graemlins/smile.gif

 

[jimbaerselman]

Re: Two anchors

I'd never heard of a Bahamian moor until reading Pelican Pete's contribution: http://www.pelicanpower.com/abacoguide/bahamianmoor.htm

To me, there were two ways of using two anchors for differing situations; wind rode and tide rode. I'm sorry if using the 'b' word caused confusion - fight it out with Pelican Pete!

 

[vyv_cox]

Re: Using two anchors

No, ran them both over the twin bow rollers. The Delta and chain are on the starboard roller, I set the anchorplait over the port roller but threaded through a length of 1.5 inch PVC tubing to prevent chafe. I cannot see any benefit in lashing them together in our circumstances but I suppose in tidal conditions there might be a case. Not something I would relish doing.

 

[ChrisE]

Re: Two anchors

No offence intended, my only concern was that someone would get the wrong end of the stick.

And at the end of the day all that matters is that the boat doesn't drift off, doesn't hit other boats and is as comfortable to live aboard as possible

 

[roly_voya]

Re: Two anchors

Craig

You say some of the maths in Alain Frayssee site is unsound. Would you dispute the idea that, in practice with sensible roads laid, during wind gust the anchor load rises by a factor of about 2x the increase in loading from lull to gust. This seems to be the determenting factor that causes anchors to break out and start a drag. If you do what sort of factor would you allow?

all

Some interesting comments on tendom anchors and why they may not work, makes sense so food for thought. Those that said they found it didn't work what sort of gap wher you using between anchors? wonder if this makes a difference? Obviously if they where directly shackled together the back one would be in the hole dug by the front one. Alternitively if they where 20m apart this would seem unlikely.

The techneque I have used is to have about the water depth seperating anchors, allow boat to drift slowly back and lower first one, give it a check to get it to bite before the second one lands, then continue paying out to about 3x scope. Set and check holding then pay out to 7-10x scope. If there ain't room go elsware. Never had the chance to dive and view the effect but will definatly do that now.

Anyone Use fishfindes to look at the bottem characteristics before anchoring, do they work?

 

[hylass]

Re: Two anchors

[ QUOTE ]
<span style="color:blue"> Some interesting comments on tendom anchors and why they may not work, makes sense so food for thought. Those that said they found it didn't work what sort of gap wher you using between anchors? wonder if this makes a difference? </span>

[/ QUOTE ]

During his anchor test (published in PBO - july 2002) Pr Johm Knox wrote:

" Where an anchor was dragged, a trench formed behind it and is quickly backfilled with loose, uncompacted sand - These areas were clearly visible after several tides and may explain why some popular anchorages are criss-crossed with patches of poor holding.."

When using tandem anchoring, they are a lot of chances that the most distal anchor will fall into the trench left by the first one..
and this is enough to explain why two tandem set anchors doesn't have twice the holding of one single anchor..

 

[vyv_cox]

Re: Two anchors

I have real difficulty in understanding how tandem anchors could possibly work. OK, I accept that people have done it, their boats didn't drift away, so they assume that the technique is a good one. However, in most other similar situations it is a fact that where two similar items are placed in series to 'double up' their effectiveness they don't do it. What happens in many situations, sealing high pressure being the one I am most familiar with, is that one seal (anchor?) does all the work while the other simply freewheels, doing nothing.

I cannot understand how the load could possibly be divided between an upstream and downstream anchor. I can believe that the downstream one could help with achieving an initial set but after that I suggest that one does the holding, the other does nothing. Which is the effective one is solely a matter of size, weight, bottom holding and other factors.