RichardS
N/A
Yes, it's all in vgc ..... in fact 50m of it were brand new a couple of years ago.
Richard
Rocna reversal phenomenon
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Yes, it's all in vgc ..... in fact 50m of it were brand new a couple of years ago.
Richard
Neeves
Well-Known Member
My chain is 10mm. My bent link is made of 12.5mm round bar. I doubt if the difference in pulling it through the mud, compared to pulling the length of chain it replaces, could be measured. It's holding us right now
I measured it:
Changing from 6mm to 12mm chain reduced anchor depth by 25% (shear stress of the seabed increases with square of depth). So chain size does impact. A Boomerang/Banana is short - but it is immediately adjacent to the anchor. Its about choice - if I were you, I'd stick to what I have (it will make an imperceptible difference) - if I were buying from new - I'd think about it and if I could source the components/raw material easily - I'd go the thin route.
if you 'think thin' at the outset (before you have committed to 100m of 10mm chain, say) then every little helps. Cut out the big chunky swivel, use smaller chain - its cumulative.
Obviously if you already have the chain (you are unlikely to change) but other things - like the big chunky swivel (that are not contributing) might merit consideration for retirement. If you are commissioning a new yacht - its part of the equation - which you can discount for other reasons - but at least it can be something to think about.
Jonathan
Neeves
Well-Known Member
I can second that. Even with my slotted bow roller it still twists itself again even after letting the whole lot out in deep water to untwist it.
Rihard
I concur
Anchors are not precision pieces of engineering, despite what anchor makers might say. It is known anchors are hydro-dynamic - they align with water movement (see previous posts in this thread).
it is not impossible that anchors act like a propellor and rotate as they are deployed or retrieved (when they are subject only to gravity and water flow).
Hanging them and then retrieving may in itself cause chain twist.
Our windlass is incredibly fast - too fast to watch the chain with any accuracy - and certainly fast enough to cause rotation if the anchor is not perfectly balanced.
We would tend to retrieve until the anchor is hanging free about 2m below the bow roller and then leave to settle - but it can still not be perfectly aligned, hence the Boomerang.
Jonathan
NormanS
Well-Known Member
Hi Jonathan, I think you're confusing me with somebody else. I don't have a swivel!
By "not measurable", I'm comparing 200mm of smooth 12.5mm round bar, with 200mm of nobbly 10mm chain. Try pulling each one through mud, and I don't think you'll find any significant difference.
Neeves
Well-Known Member
Norman - I was not suggesting you had a swivel (I know you better than that!). I was generalising.
When I walk round marinas I see lots of swivels, more people use them than don't. They are often used in combination with shackles from nefarious sources. Swivels contribute nothing, they are a weak link and detract from anchor performance - I try to make these points when ever I can. its odd - people try to keep costs down - and then go out and buy a useless and dangerous.component.
More anchors are lost through shackle or swivel failure than anything else. Good shackles are cheap - why risk your Stg400 anchor for any savings you can make on a shackle and increase risk of loss through use of a swivel - beggars belief.
Norman, Apologies for any confusion.
Jonathan
When I walk round marinas I see lots of swivels, more people use them than don't. They are often used in combination with shackles from nefarious sources. Swivels contribute nothing, they are a weak link and detract from anchor performance - I try to make these points when ever I can. its odd - people try to keep costs down - and then go out and buy a useless and dangerous.component.
More anchors are lost through shackle or swivel failure than anything else. Good shackles are cheap - why risk your Stg400 anchor for any savings you can make on a shackle and increase risk of loss through use of a swivel - beggars belief.
Norman, Apologies for any confusion.
Jonathan
Brent Swain
N/A
A wide enough bow roller lets my Delta flip itself over, once the shank comes high enough over the roller.
thinwater
Well-Known Member
a. Don't motor forward when raising.
b. Align the chain correctly from anchor to gypsy (no twist).
By doing these two things, and NOT having a swivel, my anchor comes up right 95% of the time. If this does not work The chain is jumping on the gypsy. Investigate that. Not a theory, but a geometric certainty.
Very, very simple.
b. Align the chain correctly from anchor to gypsy (no twist).
By doing these two things, and NOT having a swivel, my anchor comes up right 95% of the time. If this does not work The chain is jumping on the gypsy. Investigate that. Not a theory, but a geometric certainty.
Very, very simple.
jiris
Well-Known Member
Thank you and all the other "antiswivel" gurus. I can see the light
. Will remove these gizmos from both my anchors at the nearest convenience.Solent sailer
Well-Known Member
We do something similar just a case of getting the water flow in the correct direction, as for the swivel we had to fit one as even after fiddling with the alignment when the windlass put the final tension on the chain it would jump off the gipsy and drop the anchor and 40m of chain in the water!
BelleSerene
Well-Known Member
I wonder why? My arrangement, a 20kg Rocna with 10mm chain, very deliberately no swivel, and the starboard bow roller of our 39’ Beneteau, never fails to self-right. Ever.
Yes, there can be rotation, owing to the hydrodynamics of retrieving the anchor with forward motion through the water. But the anchor self-rights on the bow roller every time.
Seems to me that three things contribute to this.
1. The curve of the Rocna’s shank and the slim profile of the shank compared with an I-bar, making the anchor sit unstably upside down
2. The twisting force of the chain, which works because I’ve fed it through the gypsy so as to be untwisted when the anchor is in its final position on the bow and because there’s no swivel in line to re-introduce twist
3. A relatively broad bow roller, which gives the anchor’s shank space to flip over when (as usually happens) the anchor comes on to the roller upside down and the chain’s twist provides the rotational force to turn it off its unstable position on its back.
2. The twisting force of the chain, which works because I’ve fed it through the gypsy so as to be untwisted when the anchor is in its final position on the bow and because there’s no swivel in line to re-introduce twist
3. A relatively broad bow roller, which gives the anchor’s shank space to flip over when (as usually happens) the anchor comes on to the roller upside down and the chain’s twist provides the rotational force to turn it off its unstable position on its back.
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vyv_cox
Well-Known Member
We have had this argument many times. My advice is: if you don't need a swivel, don't have one. If you find it beneficial, have one but make it a good one. Our Rocna also persists in coming up the wrong way round. Even in the season that we spent without a swivel, at the urging of those here who say it is unnecessary, the Rocna still emerged from the water back-to-front. When it did it was quite difficult for me, and impossible for Jill, to turn it the right way up due to the short distance between our bow roller and the windlass. A swivel removes this problem totally, as it can be rotated easily by hand before it is hauled over the bow roller.
As Jonathan has written, our Osculati experiment did not go well. We dragged when using it several times and once in a position to investigate we found that the chain wrapped around the 'wrong' end, resulting in the swivel pointing skywards. I am not quite sure why this caused us to drag but assume that sometimes it finished up pointing downwards instead, which caused the anchor not to set correctly. I do not know if a 'banana' does the same thing but I shall stick to my Kong plus three chain links.
As Jonathan has written, our Osculati experiment did not go well. We dragged when using it several times and once in a position to investigate we found that the chain wrapped around the 'wrong' end, resulting in the swivel pointing skywards. I am not quite sure why this caused us to drag but assume that sometimes it finished up pointing downwards instead, which caused the anchor not to set correctly. I do not know if a 'banana' does the same thing but I shall stick to my Kong plus three chain links.
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Neeves
Well-Known Member
BelleSerene - Anchor chain galvanising is inconsistent from the same supplier - why think each link could be perfect in shape. A slight imperfection in each link could allow the anchor to lie at 90 degrees to the correct angle.
Some bow rollers are too narrow (or shanks too wide) to allow an anchor to self right
Some bow rollers are too narrow (or shanks too wide) to allow an anchor to self right
RichardS
N/A
patrigo
New Member
My Rocna Vulcan comes up any way it wants, I don't give a damn. As soon as the winch starts to pull it over the roller, it is no longer hanging freely vertical and aligns itself correctly, immediately. I do not have to help it. Maybe because my bow roller is in a significant "valley", due to the side plates, and the anchor cannot fall out, so the centre of gravity causes it to rotate as it is pulled out of the hanging position. Any help?
vyv_cox
Well-Known Member
I agree. No idea why the alignment of the chain should alter as we always motor the anchor down but no doubt it does.Nope, it's not.
Richard
thinwater
Well-Known Member
Nope, it's not.
Richard
I hear what you are saying, but my chain never rotated in the gypsy, not in 10 years. So it was just that simple. I can only gather it is a matter of proper fit of the chain to the gypsy, enough fall into the locker (my locker is deep), and windlass type (vertical in my case). I swear, I'm not making this up.
And yes, unless the chain moves in the gypsy, it is as sure as 2+2=4 that the chain will remain aligned. It is certainly possible for a twist to sneak over the roller--happens every few times--but it is simple to remove by rotating the chain as you lower a little bit, and even easier if the anchor is rested on the bottom for a moment. I typically fix this before the anchor breaks the water, since it is visually obvious. If that does not work, there is a design problem with the roller (the V and the grove width).
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biscuit
Well-Known Member
Having originated this thread, I will restate: the anchor ALWAYS come up reversed by 180 degrees, not 90 degrees or any angle between, which seems to negate some theories regarding chain twist. (although no doubt someone here could correct me)
Neeves
Well-Known Member
Biscuit,
I think we all, or mostly, understand what you are saying - we may not understand the specific reasons for your issues and are simply covering all the options of which we know.
Drop your chain 1m, better drop so that you can still clearly see it in the water (drop it with your windlass) - what is the orientation of your anchor hanging free? Is the toe forward (so back to front) or back (so right way round).
Now - retrieve the anchor 300mm (1') at a time, how does the aspect of the anchor change, if at all. How does it, or the shackle, arrive at the bow roller.
Jonathan
I think we all, or mostly, understand what you are saying - we may not understand the specific reasons for your issues and are simply covering all the options of which we know.
Drop your chain 1m, better drop so that you can still clearly see it in the water (drop it with your windlass) - what is the orientation of your anchor hanging free? Is the toe forward (so back to front) or back (so right way round).
Now - retrieve the anchor 300mm (1') at a time, how does the aspect of the anchor change, if at all. How does it, or the shackle, arrive at the bow roller.
Jonathan
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NormanS
Well-Known Member
Well, at least yours is predictable. I never know which way my non-rocna anchor is going to present itself. That is why I made my "bent link". It has completely solved the problem. Now irrespective of which way the anchor comes up, it is automatically rotated correctly, as soon as the bent link reaches the bow roller.
