The Weakest Link?
Upon his return after a storm, one of our friends discovered that his modest schooner was missing from its mooring. It was eventually located several miles away, grounded on a shoal, having found its way around navigational aids, between power line towers, past fishing piers, and even through a bridge span, somehow sustaining nary a scratch.
Our friend ultimately determined that a missing clevis pin in the ground tackle was the culprit that allowed his boat to come free of its anchors, most likely because the cotter pin had gone missing. And he’s far from the only boater with similar stories; in another incident, a boat broke loose in a storm and was driven ashore, where it sustained significant damage. When the anchor was recovered, only half of a swivel was still attached.
Scenarios like this lead to considerable controversy—and rightly so—about the use of swivels in ground tackle. As components go, especially in rough weather, swivels are often considered a weak link.
There are definitely situations in which a swivel can be beneficial, and possibly even necessary. When the boat is anchored in a place where the wind or current repeatedly change directions, a swivel can minimize twists in the rode. When the boat is moored with all rodes brought to a central ring, a swivel installed between this ring and the pendant that leads to the vessel can prevent the rodes from wrapping around one another. And, in order to house the anchor, the anchor must be rotated. Alternatives other than a swivel are impractical.
So, we have swivels, which means we need to understand the situations that most often cause them to fail. In most cases, the failures revolve around three issues: using the wrong style of swivel; attaching the jaws of a swivel directly to the anchor; and using understrength swivels.
Fortunately, all three of these problems have simple solutions.
The first is making sure to use the right style of swivel. They come in several styles, including jaw/jaw and jaw/eye designs—both of which you want to avoid.
Neither of those styles can be recommended for use in ground tackle, as they have several weaknesses that often lead to failure. The cotter pin that holds the clevis pin in place can break or come out, allowing the clevis pin to back out; the jaws of the swivel can be forced apart, shearing the cotter pin and allowing the clevis pin to back out. With one end immobilized, a side load at the other end of the swivel imposes a bending load on the swivel’s pivot pin, and with a load as little as half of the swivel’s rating, this pin can break. And, if you use the jaws to attach the swivel directly to an anchor, the swivel can incur side loads that force the jaws apart or place a bending load on the pivot pin.
What you want, instead, is the eye/eye style of swivel. It’s a better choice for ground tackle because, absent a jaw, it eliminates the possibility of the swivel being attached directly to the anchor. It also has no clevis-cotter pin combination, so that point of failure is not present. And, because each end of an eye/eye swivel must be connected to its adjacent partner with a shackle, there is universal movement at both ends of the swivel. This double-end universal movement greatly decreases opportunities for a bending load to be imposed on the swivel’s pivot pin.
Once you have the right kind of swivel, you’ll need to connect it to the type of chain you have on board. When connecting swivels to G3 chain (commonly called proof coil or BBB chain), you can use the kinds of regular-strength, carbon shackles found in hardware and big box stores. Those are designed to fit and match the work load limits of G3 chain.
However, if you’re connecting swivels to high-test G4 chain, then you need to use high-strength alloy shackles. They are the only shackles designed to fit and match the work load limits of G4 chain. Unfortunately, alloy shackles are not as easy to find as carbon shackles. A few chandleries carry them, as do many industrial supply facilities. Look online to buy ones made by The Crosby Group, Campbell Co. or Titan Marine Products.
Also look for swivels that, in the United States, are manufactured to the federal specification known as RR-C-271-E, often referred to as 271E or simply 271. A swivel manufactured to this standard will have the size of the swivel embossed on it in raised numbers. However, unlike on shackles, there will be no indication of a work load limit. For a swivel’s work load limit, you have to go to the 271 standards or to the manufacturer’s literature.
Sizing is also a consideration. The swivel’s work load limit needs to equal or, better yet, exceed the maximum load that will be imposed on the ground tackle. Should there ever be a possibility that the swivel will experience side loading, go bigger. Choose a swivel that is at least one size larger.
Materials matter too. With stainless-steel swivels, you should have all of the same concerns that are mentioned above. However, stainless-steel swivels are not included in the 271 standard, so you need to be cognizant of the point where bending moments can be incurred, as well as the swivel’s load rating, be it in straight line pull or when side loaded.
The bottom line is that you want to prevent the swivel from being the weak link in your ground tackle. Look to use a swivel that is of good quality, design and strength, and then make sure it’s installed properly. If there is ever an inkling that a swivel will incur loads that could make it fail, it is best to remove it.