Anchor/chain/rope

vyv_cox said:
... but still confused as to the reason my anchor doesn't always come up the same way...
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Me too! But the explanation may be just due to the sum of lots of small, random, twists. Very 'back of cigarette packet' stuff, but note that chain is made so that the inside diameter of the link's 'loop' is at least 1.5x the diameter of the wire itself (eg 8mm wire, 12mm inside link) see http://www.williamhackett.co.uk/en-...bulk_chain/grade_30_short_link_chain/p-107153.

This means that the potential energy minimum when chain is under tension is not V shaped but very U shaped, or even flat bottomed - a complicated way of saying that the chain can twist a bit on each link even when under tension, maybe by +/-10 degrees or so at a guess, and for this exercise let's assume these twists are uniformly distributed between -10 and +10 degrees, with a mean of zero.

In the length between windlass and anchor there may be 30 links. Convolving the small random twists of the 30 links gives this distribution:
distr_conv_30.png

As you can see, there is some chance that the twist is greater than 90 degrees, whereupon the anchor will, irritatingly, flip over on the roller.

I'm not at all sure this is the explanation, and as I said the numbers are just initial guesses.
 
jdc said:
Me too! But the explanation may be just due to the sum of lots of small, random, twists. Very 'back of cigarette packet' stuff, but note that chain is made so that the inside diameter of the link's 'loop' is at least 1.5x the diameter of the wire itself (eg 8mm wire, 12mm inside link) see http://www.williamhackett.co.uk/en-...bulk_chain/grade_30_short_link_chain/p-107153.

This means that the potential energy minimum when chain is under tension is not V shaped but very U shaped, or even flat bottomed - a complicated way of saying that the chain can twist a bit on each link even when under tension, maybe by +/-10 degrees or so at a guess, and for this exercise let's assume these twists are uniformly distributed between -10 and +10 degrees, with a mean of zero.

In the length between windlass and anchor there may be 30 links. Convolving the small random twists of the 30 links gives this distribution:
View attachment 46246

As you can see, there is some chance that the twist is greater than 90 degrees, whereupon the anchor will, irritatingly, flip over on the roller.

I'm not at all sure this is the explanation, and as I said the numbers are just initial guesses.
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Interesting explanation that has much merit. Unfortunately in my case, my bow roller is grooved to take the chain, so any twisting between bow roller and anchor should be taken out once the anchor arrives. Until you have sailed and anchored in the clear waters of the Med it is difficult to appreciate just how much an anchor revolves as it is being recovered. My Delta and Rocna turn once every metre or two and i have seen CQRs doing something similar.
 
vyv_cox said:
... in my case, my bow roller is grooved to take the chain, so any twisting between bow roller and anchor should be taken out once the anchor arrives...
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So's mine, which is why I quantised the possible orientations of the anchor to be only one of two, ie right way round or upside down (with a 90 degree threshold).

But I don't think that the chain is stopped from rotating by the groove because the part of the circumference of the roller that the chain is in contact with is several links long, which seems to spread the load as it were, and thus seem to lie equally happily at any angle despite that groove.
 
If the anchor twists once per metre then it has nothing to do with tide or wind. The twists must be imposed as the anchor is deployed or is retrieved, or both. If there are twists every metre - what happens if you hang a length of chain up 'freely' does it hang twisted? Anchors are probably not perfect, can the act of lifting cause a hydrodynamic effect because of imperfections - they would always twist the same way if this was the case.


Vyv - you do not like sex nuts - is that because the thread is a weak link or because the male component falls out? I have known of them fall out. They were used on an older brand of deck car and fell out. they need to have Loctite. But if its the assembly is weak then the Loctite will, obviously, add no strength.

Jonathan
 
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Many people say that a swivel does not swivel under load, which is not much of a surprise - its hardly a sophisticated bearing.

I wonder if the anchor would self right by itself. The chain only needs to make half a turn and thats from the total of a small turn for each link (the ones between shackle and windlass) and the fluke will offer a pretty hefty turning moment.

Jonathan

edit, Norman, see post 16 above, made a bent link which self rights the anchor. With no disrespect to Norman, its a very simple and cheap device, and (all credit to Norman) works perfectly at self righting an anchor. You can buy a commercial version (for lots and lots of money) which also has a swivel incorporated and is lovely and complex - but Norman's has no moving parts and no joints at which to fail. close edit.
 
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I think a swivel is basically unnecessary. I have not used one for many years. The only problem is in conditions of reversing wind/current where the rotation occurs in the same direction.

This can wind up the chain. As the anchor is retrieved this twisted chain is concentrated ultimately between the anchor and the windlass when the anchor is at 1:1 and is being broken out. If there is enough twist in the chain it can bunch up like a wound up elastic band. The twisted chain prevents the windlass working and is a difficult problem to fix.

To put this into perspective I have only experienced this twice in the last 2,000 nights at anchor. I don't feel this problem is sufficient reason to use swivel, but if you anchor for long periods in conditions where you rotate around the anchor, it is a problem that is worth considering.
 
But ignoring twisted chain (which some people obviously think a major issue given the numbers of swivels, usually incorrectly attached, I see on ground tackle) many suggest their anchors arrive at the roller 50% of the time back to front - which is only a 180 degree turn - Norman's bent link is the answer - and would be highly applicable to anyone with an anchor too large to 'man' or 'woman handle'. To have an anchor self right by itself on the bow roller puts an enormous strain on the windlass and even turning a small anchor is not the best thing for your back.

But always have a few links of chain between your bent link and anchor.

Norman had some images on an earlier thread - but cannot for the life of me recall what the thread was about, but something to do with anchors:)

Jonathan
 
noelex said:
This can wind up the chain. As the anchor is retrieved this twisted chain is concentrated ultimately between the anchor and the windlass when the anchor is at 1:1 and is being broken out. If there is enough twist in the chain it can bunch up like a wound up elastic band. The twisted chain prevents the windlass working and is a difficult problem to fix.
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I watched this happen on a charter boat in the Ionian a few years ago. The anchor twisted so violently as it left the water that it knocked a chunk of gelcoat off the bow of the boat.

Sex nuts: AFAIR every swivel and connector that was fitted with this arrangement failed there. The forged pin as used by Kong and Osculati is the thinnest part, so will also be the most likely failure point, but in practice was almost twice as strong when it bent, releasing the chain.

The swivel with the long bent arm, by Osculati, was a good performer. Its failure load was a good bit better than the Grade 30 and 40 chain.
 
noelex said:
I think a swivel is basically unnecessary. I have not used one for many years. The only problem is in conditions of reversing wind/current where the rotation occurs in the same direction.

This can wind up the chain. As the anchor is retrieved this twisted chain is concentrated ultimately between the anchor and the windlass when the anchor is at 1:1 and is being broken out. If there is enough twist in the chain it can bunch up like a wound up elastic band. The twisted chain prevents the windlass working and is a difficult problem to fix.

To put this into perspective I have only experienced this twice in the last 2,000 nights at anchor. I don't feel this problem is sufficient reason to use swivel, but if you anchor for long periods in conditions where you rotate around the anchor, it is a problem that is worth considering.
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Agree - the chain starts unwinding as soon as the anchor unsets. Even a CQR turns over as it enters the roller. I've tried both, with and without, and can see no difference in performance. Vyv was going to report on his experiences with and without a swivel. I confidently looked forward to his confirming my prejudices... ;-)
 
Scotty,

You seem to be using an Oscallati swivel which combines the swivel with a complicated version of Norman's bent link. Just so that you are totally happy - these, or the ones Oscallati sell, are made in China. The Chinese manufacturer looks to be professional and actually is in the middle of having all of their items tested and the WLL etc stamped into the components.

I'm not sure of the value of the swivel part of this unit. as the swivel under load will be at an angle (and even less likely to swivel than a normal swivel). The bent part of the unit is the component that 'rights' the anchor. I would put some links of chain, we use 9 links, must be an odd number, between the unit and anchor. It gives more room for the anchor to rotate. But you might not have room for 9 links, shackles and the Oscallati unit, just put in as many as you can.

As with most windlass and swivel films the action was too quick, and the swivel was not the central feature. I did not really see how the swivel operated - next time take another with the swivel in the key role!:)

None of this will do anything for the weed, which will be an issue with any anchor as its caught up round the shank.

Jonathan

edit: Vyv seems to like these units and I think has said they are well engineered. I think he features them on his website. I'm not keen on the swivel (partially as its unnecessary - but also because its stainless) but I'm also not keen on the second bolt that holds the mechanism together - needs good Loctite to secure. I do like the bent link. end edit
 
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J Neeves said:
I'm not sure of the value of the swivel part of this unit. as the swivel under load will be at an angle (and even less likely to swivel than a normal swivel).

edit: Vyv seems to like these units and I think has said they are well engineered. I think he features them on his website. I'm not keen on the swivel (partially as its unnecessary - but also because its stainless) but I'm also not keen on the second bolt that holds the mechanism together - needs good Loctite to secure. I do like the bent link. end edit
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I didn't say I particularly liked them but I did say that their strength was good, stronger than the chain to dispel 'weakest link' comments. They are included as one of the connectors I tested.

My only thought about the swivel itself is that if the distance between the shank end and the windlass was very short it would enable the anchor to rotate without stressing anything, which might happen with Norman's rigid version. Not really a big issue though.
 
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