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Old 10-06-2019, 22:33   #46
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Re: chain wrapping around anchor

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Originally Posted by Alan Mighty View Post
Or it could be about BOTH length of the ship (as a proxy for windage etc) AND the depth of the water.

I've noted before (Average Range of Yawing at Anchor in Storms) the common practice of cargo ship masters using the scope formula of:

Length of chain = 3H + length of hull; (where H = water depth + freeboard to anchor hawse)

That formula is often simplified to:

Length of chain = 3H + 90; (where Length is measure in metres - the 90 representing 90 metres as a nominal hull length of a cargo ship)

The UK Admiralty used an approach that focused, like Thinwater, only on H.

I've attached a graphic from one of the more common guides to ship handling in E Asia that compares the Japanese formula to the UK Admiralty formula. See: JCA Guide to Ship Handling Fig 3-2.jpg, about 115 KB
Really UK? You need to find the square root of the depth?
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Old 11-06-2019, 00:48   #47
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Re: chain wrapping around anchor

We anchor in 2+ knot tidal areas regularly and have never had an anchor wrap issue that we know of.

But apparently others do with the same same but different anchor.
https://setsail.com/bigger-is-better-with-anchors/





Yeah, I am sure anchor type has bugger all to do with it. (-;
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Old 11-06-2019, 02:49   #48
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pirate Re: chain wrapping around anchor

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Originally Posted by thinwater View Post
And weight of boat = scope? No, weight + windage = weight of anchor, with scope being unrelated (if the chain is matched in strength to the load, and thus weight by logical extension, then the catenary available and required does not change).


This isn't a multi-mono thing, this is a maths/geometry/physics thing. The scope used by a multi-thousand ton ship is on the same order as a 20 boot boat. That is what the maths and experience say. If you apply your formula to a large freighter you also get a comical result. A panmax ship would need to lay 3x950 + 50 = 2900 feet of chain in 50 feet of water, or a scope of over 40:1. They don't.



No, it is not about weight or the length of the boat, it is about the depth.
Its not a mono - cat thing.. I was yanking your chain
I will stick to my way thanks, its kept mme safe as those around me drag..
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Old 11-06-2019, 08:18   #49
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Re: chain wrapping around anchor

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Originally Posted by Seamentress View Post
Ok, I don't usually post much on here, but read a lot!
Firstly, I live aboard, here in La Paz, I am one of the small community who make up the Mogote fleet. We usually have two tides a day here, and on big Spring tides, the current can reach 5Kts, that's 5 in and 5 out, I arrived here in 2011 and have seen 2 hurricanes come through and numerous storms.a
I am also a member of our hurricane response team.
I have attended and helped recover numerous boats during that time, probably upward of 50, so I think I can contribute to this discussion with a higher than average degree of experience.
First to the question of the Bruce anchors.
In my experience the Bruce is the anchor giving the highest failure rate in these conditions, in almost every case when a dragging Bruce anchor has come up, it is inevitably wrapped, often in a huge ball of chain, several times it has been necessary to lower the ball into a volunteers dinghy to unwrap it, being too heavy and awkward to get aboard the owners vessel.
So, Bruce anchors, in my experience are prone to fouling when a boat swings from one end of the scope to the other.
I have talked to the owners about how the anchor was set initially, and almost all of them use their normal methods, and scope. One of the common denominators comes to mind, that most of them don't allow enough scope out to bury the shaft when setting the anchor, this leaves a small enough gap between the sea bed and the anchor shaft for the chain to get wrapped, after several tides, the anchor eventually gets pulled out backwards and the boat is off to either the nearest neighbour or sandbar whichever comes first.
Also a greater scope of 7:1 or more helps to minimise this issue, I have seen two boats anchored close to one another with exactly the same ground tackle, one dragged in a Chubasco storm which came up very suddenly, the other was secure! The only difference we found was one was on a long scope the other on everyone's usual of 4:1 / 5:1.
I have never seen a Rocna anchor behave in this manor, and there are plenty of users here.
The principal difference between these two anchors, is the roll bar on the Rocna, it keeps the chain from going underneath that small gap and prevents a wrap, so my advice would be to get a roll bar welded to your existing Bruce if you are anchoring in an area of tidal change, or swap it for a Rocna, and put out more scope, especially if you are sticking with the Bruce. Good Luck, stay safe!
Paul
This is exactly my experience in La Paz which I posted on page 1.
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Old 12-06-2019, 21:57   #50
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Re: chain wrapping around anchor

I anchored in tidal areas and in a river with strong variable winds hundreds of times over 20 years with three different boats, all equipped with Claw anchors, and have not fouled or dragged any of them once. What was I doing wrong?
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Old 13-06-2019, 00:17   #51
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Re: chain wrapping around anchor

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Originally Posted by Lost Horizons View Post
I anchored in tidal areas and in a river with strong variable winds hundreds of times over 20 years with three different boats, all equipped with Claw anchors, and have not fouled or dragged any of them once. What was I doing wrong?
You weren't following our advice here!!
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Old 13-06-2019, 04:19   #52
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Re: chain wrapping around anchor

Have been using a Vulcan for 3 years now. Have drug once last week in probably 100+ anchorages. Wind shifted 180 degrees in a squall and was a soft weedy bottom.

That is when set well. Does not do well in soft mud. Maybe a larger Vulcan would be better in mud.

Anyhow, it fouled on itself once when launching. Has never been a problem fouling when current changed.

But if an anchor can hook the bottom surely there is someway to hook the chain also. One time I anchored with 2 anchors and left my boat for a few weeks years ago. Got back and all looked good. But found both anchors had fouled each other!
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