How Well Do Swivels Reduce Twist?

Posted by Darrell Nicholson with Jonathan Neeves at 05:43PM - Comments: (8)

 

In the upcoming March issue of Practical Sailor, PS testers dig into anchoring accessories, among the items we look at is new stainless-steel anchor swivel from Mantus. We know the theory behind using an anchor swivel: The swivel releases any twists in the chain when an anchored boat swings through 360 degrees or more. Still, as I've addressed in previous blog posts, we question the logic of using one. Our skepticism is supported by our own experience, previous testing, and input from long-term cruisers, but we also wanted to devise a test to investigate chain twisting.

We took 30 feet of 5/16-inch chain and freely suspended it roughly horizontal between two secure points. We tensioned the chain to about 90 pounds of load. We had a swivel at both ends; the top swivel was a standard cheap swivel that allowed us to manually twist the chain. At the anchor end, we tried two different name-brand swivels, the Mantus swivel (for sizes 5/16-inch to 3/8-inch chain) and a 5/16-inch, galvanized Acco swivel.

Working from the top, we twisted the chain to find out how many twists in produced enough torque to allow the attached Mantus or Acco swivel to release the turns.

The results were surprising. The Acco galvanized swivel took eight complete twists in the chain before it started to turn, and the Mantus swivel took 6.5 turns. Given that typically skippers might be deploying three times the amount of chain we tested with, it is obvious that several more turns—possibly three times as many—would be required for the bottom swivel to make any difference.

In order to transmit torque onto the swivel, the chain will need to free of the seabed, requiring more load (about 160 pounds for 100 feet of 5/16-inch chain in 20 feet of water), and the torque required to release twists will be higher than in our simple test.

In our view, it is unlikely that the swivel will reduce anything but a large number of twists, and these twists could be removed more safely and easily by slowing down the retrieval once the anchor clears the bottom. A slower retrieval also prevents the hydrodynamic force on an unbalanced anchor that might cause it to spin. In fact, anchor spin upon retrieval with a high-speed windlass is probably the most likely cause of twist, and is often mistakenly attributed to the windlass itself. Ironically, if your anchor rotates in a beneficial direction as it comes up, the swivel might actually prevent the anchor’s rotations from untwisting the chain.

If your anchor chain is twisted to the point that it is forming hockles or causing it to jump from the windlass, you will want to deploy all the chain, untwist it manually, and load it back into the locker. You can do this ashore (and mark your chain lengths at the same time, if needed), but it is often easier in deep water.

Unless you are retrieving the anchor so fast that it spins like a whirl-a-gig, or the tide and wind is spinning you around like a barber pole, you should not have to untangle it again for months or more. 

 

Jonathan Neeves
Jonathan Neeves

Even under light loads, and no friction from the bottom, it took several rotations of chain before the bottom swivel began to turn in our test.

Comments (8)

I purchased a Mantus swivel this fall for several design reasons but the main purpose was to help in retrieval.
My previous anchor was a Manson Supreme that insisted on arriving at the roller backwords. Turning it with a boat hook was pretty difficult even with the Kong swivel.
I have since upgraded our anchor to a 66# Sarca Excel that doesn't have a hoop. I tried using a swivel but it also proved difficult to turn a heavier anchor that continued to come up backwards. Then I saw the design of the Mantus swivel. It's designed to be safety wired. It has a larger rotating surface so if the anchor isn't already in position to retrieve it very easy to adjust. I've not seen my chain twisted from anchoring in opposing wind-current situations but this swivel has worked for anchor retrieval.

Posted by: JimSailing16 | February 20, 2016 5:43 PM    Report this comment

We found that a swivel tends to allow the anchor to come up "wrong" more often than not. They are simply unnecessary.

Posted by: khaverland | February 12, 2016 6:49 AM    Report this comment

I guess I missed the point of an anchor swivel altogether. I was never concerned about twist in my all chain rode. My only concern has been retrieving my 65 pound Mantus anchor onto my 46 foot sailboat. Because of some residual twist in the chain rode, sometimes when I bring the anchor out of the water it is facing in the opposite direction necessary to smoothly bring the anchor aboard with my windlass. I'm out there on the foredeck with one foot on the anchor retrieval foot switch while I lean over the bowsprit with a boat pole in hand trying to twist the anchor in the appropriate direction to bring it aboard. All this while my wife begins making head way because, of course, we are no longer anchored. For this purpose, an anchor swivel would eliminate my need to be a contortionist. I had a anchor swivel on my two previous sailboats, but was scared away by Practical Sailors' articles on the issue. For the above reason, I am considering adding the new Manus swivel to my rode.

Arnon Garonzik
S/V Vision Quest
Annapolis, MD

Posted by: agaronzik | February 11, 2016 10:58 AM    Report this comment

And we excluded the grit that is driven into the swivel during its life underground.

Posted by: Drew Frye | February 4, 2016 7:04 AM    Report this comment

I have come to believe that the twist comes from the anchor roller as it roles the chain down to the bottom of the V shape. With over 300' of chain it is hard to relieve the twist that forms cockles that jam the chain.

Posted by: Avidsailor | February 3, 2016 5:42 PM    Report this comment

Funny thing, I put a swivel on by boat for this very reason many years ago and my chain goes through a hawse pipe. My chain got so tied up it would jam up in a knot inside and the only way I found to get it untangled was to do it ashore, so far so good but it been out only a half dozen times.

Posted by: philwilliams@videotron.ca | February 3, 2016 2:49 PM    Report this comment

I wonder if the swivel would be any more inclined to turn if it were underwater and lubricated by the water, rather than dry. Also as an anchor is being retrieved the chain is vibrating and moving quite a bit; I wonder if that movement would help overcome the static friction that prevents the initial untwisting you saw.

Posted by: Davidasailor26 | February 3, 2016 2:23 PM    Report this comment

Another consideration: Do a pure tensile test as you have done on chain in the past with no swivel and 8 or more rotations in the chain over a 20' span (or whatever that equates to in the test segment of your machine) to ensure that the overall strength of the system has not degraded with the twist in the chain. It may turn out that with a twist the 'weak link' is no longer the swivel. Be careful; when it breaks not only will the tension be released the torque will too. There is more energy stored in a twisted chain under tension, it will appear more elastic.

Dan Mielke
Strange Bird
NSB, FL

Posted by: DanoMielke | February 3, 2016 2:02 PM    Report this comment

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