PS Advisor: 08/01/04
Has Practical Sailor conducted a study of swaged terminals vs. screw-on terminals? I've heard opinions recently that the screw-on ones are preferable because they can't kink the wire (as a swage can if it's not done just right), and because they can be replaced if necessary. Also, have you done any comparisons of the two types regarding cost, safety, and longevity?
Practical Sailor rigorously tested both mechanical and swaged rigging terminals a decade ago (see May 15, 1993 issue). With characteristic candor, we titled that article "Wire Terminal Destruction Test." Information derived from those tests can help answer most of your questions as we believe the essential data regarding strength remains true today. Though the article did examine the relative costs, that information is now well out of date.
The wire in the swage fitting began to fail at 7,700 pounds of pull. The first strand of the wire affixed to the Sta-Lok fitting broke at just over 8,000 pounds, and the wire in the Norseman began to break at 7,300 pounds. Wire in the Castlok lasted until the tension reached 8,000, and the wire in the Quick Rig failed at 6,400 pounds.
In that 1993 article, we told readers that "swaged fittings, applied by an expert rigger, are strong, neat, and fairly inexpensive....The principal liability of swaged fittings is that because dirt and water can enter the terminal, they are more prone to corrosion than sealed mechanical terminals."
Among the four mechanical fittings that we tested, Sta-Lok was our top choice. The others were Castlok, Quick Rig, and Noresman. All of these fittings are reasonably straightforward when it comes to assembling them, though Sta-Lok fittings are slightly more difficult in that regard.
Ultimately, we recommended that the best arrangment would be to put professionally swaged terminals (lighter, less windage) at the upper ends of your shrouds and stays, and Sta-Loks on the bottom ends. That's a recommendation we'd make again. Additionally, if you're inclined to carry a spare shroud or stay on board for emergencies, have an eye or fork swaged onto one end and carry a spare mechanical fitting that can be used on the other end after you've cut it to the necessary length.
Our most recent work on this topic appeared in a PS Advisor that we published in the February 1, 1999 issue. In that missive we paraphrased some important information from Phil Garland of Hall Spars and Rigging: a good swage will take 100 percent of the wire strength, whereas a Sta-Lok or Norseman will yield only 90 percent of the wire strength.
As for the advantages of a mechanical terminal over a swage, the greatest edge is that these products (as you point out) give you the ability to replace the fitting yourself—almost anywhere. As for an improperly applied swage, that’s the rub, and the chief reason why it pays to have that kind of work done by an experienced rigger with a good reputation.
Regarding costs, swaged fittings are still slightly less expensive than mechanical terminals. Prices among the latter vary depending upon product, wire size, terminal style (stud, fork or eye, etc.), and supplier.