anchor scope

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Talbot

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Discussion on mobo chat about anchoring has raised an issue that affects us all. It is the amount of scope of the cable 3:1, 4:1 or 5:1. Now I would be the first to agree that 3:1 is not the answer (I actually use a different system completely, but thats another story) furthermore some boats demand more due to their behaviour when on the end of the chain (e.g. cats tend to need a bit more cause of a somewhat increased swinging around) but do we take that into account when anchoring in close proximity ?

All is fine while tide/wind remain the same, as we tend to adjust scope to get the boat into what appears to be a reasonable position compared to surrounding boats. The problem is at change of tide (and for cats sometimes at a major wind axis shift). What was a nice pattern of boats can suddenly change into dangerous proximity or even collision. The solution of course is to assess the probable position of the neighbours and try to work out a swinging circle that gives enough space - not always possible especially in Osbourne Bay. It is also the major reason for appearance on deck at tide change.

How many of you even think about this?
 

catmandoo

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How many skippers sleep soundly throughout the night at anchor ? What do you do when some one sneaks in over night for 1st night on a charter and you are awakened by a bump and thud to see a Ginormous cat alongside whose skipper has just found out that his anchor rode is rotten .

How can a Scot translate appropriate Doric curses into French at such an appropriate moment. @@@???!!!! **** = Bon soir Monsieur . Ca va bien??
 

Mirelle

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Disagree. Completely.

3:1 is ample, if you have decent gear. Longer scope than that is irresponsible in modern conditions.

Harrumph!
 

Ships_Cat

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7 Sep 2004
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We would only very rarely use more than 3:1 scope.

On 3:1 we have sat out extremely windy conditions, and also frequently go round in circles for several days in strong gusts in steep valley anchorages and have never dragged to any measurable degree (yet).

In the last 8 or 9 years we have never picked up a mooring and except on very rare occasions all the time we are away (normally around 6-8 weeks per year) we sit on our own anchor.

I have followed the MoBo thread with some interest and the main problem they have is insufficient gear to anchor reliably with. Most planing MoBo's carry very light gear.

John
 

Mirelle

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Agree with the other Cat

and in our case, 9 ton boat (well, maybe ten with the kitchen sink aboard) 12mm chain and 45lb CQR.

And a weight on a chain slider, usually one or two 28lb pigs of lead ballast carried for the purpose, if it is VERY bouncy.
 

snowleopard

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in a crowded river anchorage where we expect the tide to turn in the night i sometimes ask the neighbours how much scope they have so i can make mine the same and maintain relative positions.
 

Ships_Cat

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Re: Agree with the other Cat

Hello other catty one.

On 12 tonne boat (full tanks, all gear, etc) we use 10mm chain and a 60 lb plough anchor from a specialist anchor maker (of similar design, but not the same, as CQR).

John
 

webcraft

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Re: Disagree. Completely.

'Modern conditions'????

You mean grossly overcrowded anchorages presumably?

Mirelle, where is your tongue? In your cheek, I trust?

If conditions permit then chain in the anchor locker is just a waste of chain - the more the better.

If you have never dragged with 3-1 scope then you have been very lucky. Weight of anchor/chain is irrelevant when the wind really pipes up. It is the angle of the pull on the anchor that is critical . . . if your rode is bar tight with a straight pull on the anchor then a 3-1 scope makes a dangerously high angle for pretty much any anchor, particularly if snatch loads are introduced in a chop.

Not putting out enough scope and dragging onto other vessels can also be irresponsible. What I really hate is anchoring on a short scope - eg 3-1 - and then a load of other boats come in, the wind gets up, but you can't put out more scope because other boats are too close. I tend to put out 4-1 or 5-1 whenever I can just in case conditions change.

I never assume people have anchored using a short scope . . . thank God I don't have to anchor in 'modern conditions' very often.

- Nick
 

Ships_Cat

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Re: Disagree. Completely.

If you have never dragged with 3-1 scope then you have been very lucky.

Nope, not lucky, just know what am doing. I suspect Mirelle is the same.

Have sat on anchor in sustained 60+ knot winds and also for long periods (excess of a day) going around in circles when swirling squalls in the anchorage are taking the spray off the surface as high as our upper spreaders (approx 40 foot high).

You can disbelieve me if you wish, but I can assure you that it is so.

In 20m of water do you really let out 100m of cable and sweep out near 200m diameter circles?

John
 

machurley22

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Re: Disagree. Completely.

[ QUOTE ]
In 20m of water do you really let out 100m of cable and sweep out near 200m diameter circles?

[/ QUOTE ]

If you've got it in the anchor locker and there's room to deploy it , then why not?

"If conditions permit then chain in the anchor locker is just a waste of chain - the more the better."

In 60 knots I'd use every inch I could.

Dave
 

catmandoo

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Re: Disagree. Completely.

Ah now we get to it . Degrees of freedom :-

Depth , weight , length of rode , weight of boat ,type of boat, windage, weight of tackle , width of anchorage ,proximity of adjacent boats , strength of wind , state of swell , type of anchor , confidence of skipper .

Gettting complicated
 

Ships_Cat

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Re: Disagree. Completely.

Don't be silly, using your approach I would have all my chain out and all my warp out as well (another 120m or so).

I guess that I am experienced enough to anchor with what length is sufficient.

People may wish to dismiss what I find I can do, it is of little consequence to me. They are quite welcome to continue dragging, sweeping the anchorages clean on long scopes, etc. not accepting that maybe they could achieve better.

John
 
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