NormanS
Well-known member
That's really interesting. How does your swivel know which way to turn the anchor so that it comes home correctly?
Anchor Swivel
- Thread starter srah1953
- Start date
That's really interesting. How does your swivel know which way to turn the anchor so that it comes home correctly?
I have noted that some concave anchors align themselves with the direction of water flow such they naturally, or hydro dynamically, sit (when hanging vertically) with the base of the fluke facing the water flow and the roll bar in the 'shadow' of the flow. This means if the yacht is moving forward (and not much speed is needed) that the anchor is aligned 'back to front' as it rises.
I have only observed this with an untwisted chain - but if the yacht moves forward - then the concave anchors can always arrive back to front. If the yacht is moving back ward the opposite occurs - the anchor arrives correctly aligned to 'meet' the bow roller. My guess is that most have their yacht moving forward as they raise the anchor, as it takes load off the windlass, which means that for some (many, all?) concave anchor that as they are lifted they are raised back to front - a simple hydro dynamic effect and they would thus need some mechanism to right themselves 'at the roller' (human intervention, a self righting device etc).
I have not been sufficiently motivated to identify how many concave designs for which this is true but my observation is not unique (and is widely reported by one anchor maker as an asset) as it means when you deploy - the anchor always presents itself correctly - if the yacht (as would be customary) is moving astern.
If the observation were to be universal, for concave anchors with an untwisted chain, then drifting aft, when lifting the anchor, would result in the anchor presenting itself to the bow roller correctly - negating any need for a 'roller righter' (a device that might also be a swivel that re-aligns the anchor, using gravity, correctly).
From memory there is a similar effect for some, or our, convex anchor(s) it aligns itself naturally - but the opposite way round. Its aligned (without any chain twists) correctly when lifted, with the yacht moving forward, but back to front when the yacht moves aft (so it arrives on the seabed on its back).
Like unexplained chain twist during deployment - another of those little quirks that are annoying rather than critical.
But other observations might be interesting.
Jonathan
I have only observed this with an untwisted chain - but if the yacht moves forward - then the concave anchors can always arrive back to front. If the yacht is moving back ward the opposite occurs - the anchor arrives correctly aligned to 'meet' the bow roller. My guess is that most have their yacht moving forward as they raise the anchor, as it takes load off the windlass, which means that for some (many, all?) concave anchor that as they are lifted they are raised back to front - a simple hydro dynamic effect and they would thus need some mechanism to right themselves 'at the roller' (human intervention, a self righting device etc).
I have not been sufficiently motivated to identify how many concave designs for which this is true but my observation is not unique (and is widely reported by one anchor maker as an asset) as it means when you deploy - the anchor always presents itself correctly - if the yacht (as would be customary) is moving astern.
If the observation were to be universal, for concave anchors with an untwisted chain, then drifting aft, when lifting the anchor, would result in the anchor presenting itself to the bow roller correctly - negating any need for a 'roller righter' (a device that might also be a swivel that re-aligns the anchor, using gravity, correctly).
From memory there is a similar effect for some, or our, convex anchor(s) it aligns itself naturally - but the opposite way round. Its aligned (without any chain twists) correctly when lifted, with the yacht moving forward, but back to front when the yacht moves aft (so it arrives on the seabed on its back).
Like unexplained chain twist during deployment - another of those little quirks that are annoying rather than critical.
But other observations might be interesting.
Jonathan
vyv_cox
Well-known member
Jonathan, that's an interesting observation but I think, not having come across it before, that my Delta came up the wrong way around just as often as the Rocna does. I just put it down to Sod's Law. Maybe more research is called for this season.
Delfin
New member
It's hard to explain in words but if you look at the Ultra website they have a video. Works well by rendering the anchor unstable in any but the correct pozition for retrieval.
NormanS
Well-known member
Thanks for that. I looked at their website, and the video. Quite a classy piece of kit, with presumably a price to go with it. I have to say that even the video wasn't terribly convincing. It did work, but they had to jiggle it a bit with the swivel on the roller, to persuade the anchor to turn. Much better in action than just a plain swivel however.
As I have said already, my bow roller is extended out from the stem a little way. this gives lots of clearance to allow the anchor to rotate without fouling anything. I achieve 100% retrieval with a simple bent link, with an eye at each end. as soon as the link contacts the roller, the anchor is automatically turned the right way, without the worry of having a swivel, and with full articulation.
KellysEye
Active member
I found that a CQR swivels on the chain on the way up and thus no twists in the chain when it reaches the bow roller. We were in the Med in a bay with charter boats anchored and the wind picked up and did a 180 at night. Two boats were on the rocks in the morning both had swivels. I wouldn't use one.
Delfin
New member
I gather the bent link also works well and operates on the same principal. Since my anchor weighs more than I do, I can't wiggle it nor have I had to with the Ultra swivel. Each time the anchor comes up, if bass akwards it rotates cleanly to the correct position. What I like about the design is that it rates quite a bit stronger than the chain, so it is definitely not a weak link in the system. I've seen swivels I wouldn't use to restrain my dog, much less my boat, but the Ultra is very stout.
vyv_cox
Well-known member
I've seen loads of boats on rocks, none of them with swivels. What does that prove?
2hullsonemarinaberth
Member
Just got back from a fortnights sailing in the Caribbean 
and spent part of the time tripping over an anchor in the cockpit recovered by the skipper when he went snorkelling. 25kg anchor - no chain - one broken swivel in about 12 feet of water on a sandy bottom. Nuff said for me! I will never use one.
and spent part of the time tripping over an anchor in the cockpit recovered by the skipper when he went snorkelling. 25kg anchor - no chain - one broken swivel in about 12 feet of water on a sandy bottom. Nuff said for me! I will never use one.My observation started with Mantus' (concave) claim that as their anchor self aligned you did not need the roll bar. I tested it out and they were quite correct - if the yacht was moving aft, as it would if you were anchoring, then even a small amount of water flow ensured that (without chain twist) the anchor aligned such that the sole of the fluke hit the seabed first, the shank was aligned 'on top' ready for the toe to engage. Of course if you happened to be moving forward the anchor aligned incorrectly, or back to front, and without its roll bar would not self right if it turned up-side down. Our own anchor (convex), if we are moving forward, and no twists in the chain, then the anchor aligns, shank forward, sole of fluke pointing aft - so correctly aligned to set without it turning round - though I have only observed this with some way on, whereas the Mantus will align with very little water flow.
I do not know if this hydro dynamic effect is 'strong' enough to stop chain untwisting as you retrieve.
We do not use a swivel but some people have commented that even with a swivel they still get twists (which is hardly surprising as they are hardly a sophisticated bearing) and even good bearings are less effective under load (and even less so - full of sand). To get all the twists out when the chain is deployed you would need all the anchor chain off the seabed and a good bearing surface in the swivel
My understanding was that swivels were introduced into the rode to remove twists in chain deployed as any twists in the chain on retrieval should fall out, unless there is some natural tendency for chain to twist or stay twisted(?) as soon as the anchor is off the seabed (other than the hydro dynamic effect). So, without casting aspersions on any previous analysis of swivels - which has focussed rightly on strength, maybe we need to be looking at how effectively the stronger swivels actually remove twist - do they actually swivel in use. If they actually do not remove twist then they are a bit of a waste of time (and a waste of even more money) and the 'bent link' just ahead of the anchor would be a better (and safer) self aligning device.
So - those who use swivels, does the anchor turn as it is lifted (suggesting there might be twist in the chain, the swivel is not full effective and its a lottery which way round the anchor arrives at the bow roller). Is there a hydro dynamic effect - as if there is simply moving forward or aft might allow better alignment, best checked initially with no twists (and I've not checked how this self alignment is 'retained' once the anchor clears the water).
Jonathan
Edit, we have gone through a whole host of devices to attach anchor to chain, including a swivel, but now simply use a gal, lifting type, bow shackle. Because we have a groove in the roller and the shackle is 'horizontal' when it hits the groove and causes a jerk on the windlass (the shackle pin effectively stops retrieval for a micro-second) I lift the anchor by hand just before the shackle reaches the bow roller - but this is only possible as the anchor is small. With our situation any misalignment of the anchor does not matter as I sort it out. If I had Delfin's anchor I'd need a different technique (or join a gym!)
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Just got back from a fortnights sailing in the Caribbean
How had it broken, swivel pin snapped, 'Y' fitting broken, shackle pins broken?
Most swivels I see are bent and the shackle pin put under load.
Jonathan
Delfin
New member
The Claw I had came up backwards about half the time as well. I can't quite visualize what would happen if you retrieved it going backwards, but I suspect it would weathervane with the flukes aft - the problem I wanted to avoid. The presentation of the anchor correctly or out 180 degrees seemed completely random. At first I though it was a twisted chain, but concluded that didn't seem to be it - rather that there was no particular reason for it to come up one way or another since hanging off the chain it was balanced just fine in either direction. If the anchor wasn't so heavy, a swivel's only function would seem to be dealing with longer term anchoring and repeated circling around the hook. So I can certainly see why if your anchor can be easily man handled, perhaps a swivel adds nothing of value.
The idea that swivels are inherently unsafe is simply incorrect, although there are plenty of crappy swivel designs out there I wouldn't have either.
vyv_cox
Well-known member
Just got back from a fortnights sailing in the Caribbean
The differences between bad swivels and good ones can be seen here http://coxengineering.sharepoint.com/Pages/Connectors.aspx
Hurricane
Well-known member
Don't know if I'm talking about the same problem.
But our Delta anchor used to only come up correctly about 50% of the time.
The other 50%, it came up inverted thus making it difficult to recover.
The solution was simple - "The Twist"
Which is a banana shaped swivel - when it arrives on the roller, it immediately rotates the anchor into the correct orientation.
Here are some pics
And a video of it working
Hope this is relevant and helps
But our Delta anchor used to only come up correctly about 50% of the time.
The other 50%, it came up inverted thus making it difficult to recover.
The solution was simple - "The Twist"
Which is a banana shaped swivel - when it arrives on the roller, it immediately rotates the anchor into the correct orientation.
Here are some pics
And a video of it working
Hope this is relevant and helps
NormanS
Well-known member
I have something very similar, but home-made and galvanised, and without a swivel. It works perfectly every time. What does the swivel achieve?
vyv_cox
Well-known member
Looks like yours is the Osculati one that I tested a few years ago.
It did well, stronger than the chain, both 8 mm. All the results on my website.
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I have the same skepticism. Its been mentioned previously but many people have said that even though they employ a swivel that when they lift their anchor, and its swinging free, it untwists - which seems to suggest swivels do not actually do what is intended (twist is left in the chain when the anchor is set even with a swivel in the rode). With this, Osculati, device I would think the situation worse as the load is at an angle meaning that unless its a very clever bearing surface it will simply lock solid.
This device has the same fault of all the designs I have seen - it has a fork at one end and I can see the natural inclination is to attach the device straight onto the shank of the anchor, no wonder shanks and or swivels bend. It will also break out more easily with a side load. As Vyv points out and illustrates on his website it needs a shackle of short bit of chain between device and shank but this is simply not used by 90% of installations.
Jonathan
noelex
Well-known member
This sort of self righting swivel needs to be directly shackled to the anchor to work correctly. It relies on making the anchor unstable in the inverted position.
I do share your concern. It is a long additional lever arm to attach to the anchor shank.
The advantage of this sort of swivel is that the anchor can be retrieved from the helm without checking the anchor orientation. They are more popular for powerboats.
I don't use a swivel and on the couple of occasions the anchor chain has become wound up it develops a lot of torque. The bearing surface does not needs to be very sophisticated to work in these circumstances.
These devices do not need to be 'directly' connected to the anchor in order to work. They can be connected with, at least 11 links of chain (plus shackles at each end of the 11 links) between the device and the anchor - coincidentally I tried it about 4 hours ago. But it does rely on making the orientation of the load unstable, thus tipping the device and hence load (the anchor) such that the anchor meets the bow roller in the correct orientation. The 'bent' link could thus serve a real purpose (but I'm not convinced of the value of the swivel).
These devices and swivels should all be manufactured such that it is impossible to mount them on an anchor shank.
11 links of chain is unnecessarily long to separate anchor from 'device' (but we had an 11 link length of appropriate chain (and I hate cutting chain, or cordage). In fact for many bow layouts 11 links would be far too long and 3 or 4 adequate - you just need to have articulation between 'device' and shank such that the length of the shank is not increased. For anyone with an anchor over about 25kgs or a bow roller difficult to access I can see the bent link - self orientating unit being quite useful as it saves possibly lifting, or turning, a heavy weight to feed into the bow roller correctly and this feeding properly must be 'good' for the windlass.
You do need to ensure that any of the devices (and all the shackles they need) have a Working Load limit in excess of the chain and you also need to ensure all the connecting pins are moused and/(or) 'loctited'.
Personally I'm not keen on the idea of retrieving an anchor, any anchor plus whichever devices, from the helm as I find it difficult to imagine that this is to the best advantage of the windlass. We prefer, whenever possible, to have the chain 'fore and aft' and as near vertical as we can as we are under the idea this results in least load on the windlass - so we like to retrieve with the rode in full view.
Whereas I can see that a well wound chain develops torque, and allows the swivel to work, I find it difficult to imagine how the chain become well wound in the first place. a 4m anchorage and 20m of chain seems not unreasonable - how much winding does one need (and how does it develop) such that there is sufficient torque to allow the swivel to operate?
Jonathan
These devices and swivels should all be manufactured such that it is impossible to mount them on an anchor shank.
11 links of chain is unnecessarily long to separate anchor from 'device' (but we had an 11 link length of appropriate chain (and I hate cutting chain, or cordage). In fact for many bow layouts 11 links would be far too long and 3 or 4 adequate - you just need to have articulation between 'device' and shank such that the length of the shank is not increased. For anyone with an anchor over about 25kgs or a bow roller difficult to access I can see the bent link - self orientating unit being quite useful as it saves possibly lifting, or turning, a heavy weight to feed into the bow roller correctly and this feeding properly must be 'good' for the windlass.
You do need to ensure that any of the devices (and all the shackles they need) have a Working Load limit in excess of the chain and you also need to ensure all the connecting pins are moused and/(or) 'loctited'.
Personally I'm not keen on the idea of retrieving an anchor, any anchor plus whichever devices, from the helm as I find it difficult to imagine that this is to the best advantage of the windlass. We prefer, whenever possible, to have the chain 'fore and aft' and as near vertical as we can as we are under the idea this results in least load on the windlass - so we like to retrieve with the rode in full view.
Whereas I can see that a well wound chain develops torque, and allows the swivel to work, I find it difficult to imagine how the chain become well wound in the first place. a 4m anchorage and 20m of chain seems not unreasonable - how much winding does one need (and how does it develop) such that there is sufficient torque to allow the swivel to operate?
Jonathan
noelex
Well-known member
I don't usually anchor in same place for long, so I have only developed this twist on a couple of occasions. (About 0.1% of anchorages)
If the boat swings around in the same direction the chain is twisted. As the gypsy only retrieves the chain straight the twists are compressed into the last short section of chain between the anchor and the windlass. Many anchors will break out on retrieval with this twisting force, but if the anchor is well set you end up with some very twisted chain that cannot be retrieved normally.
I have on couple of occasions developed a high twisting force. I don't feel this infrequent problem warrants the complication of swivel, but if you anchor in same place for a long period it is worth some consideration.
The twisting force is high and I have no doubt a swivel would have "swivelled" even if the bearing was poor. (My guestimation is that it torque would be enough to twist and destroy a shackle that was a couple of sizes smaller than the chain, although you would not have such a weak link in the system it gives some idea of the force involved.)
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