FATIGUE

“… stainless steel fatigues.  No, this is not an all-metal army uniform.  It refers to the characteristic of alloyed steels of hardening and becoming brittle and age.  The more heavily a piece of alloy is stressed relative to its ultimate strength, the faster it will fatigue.  Therefore, you’d survey lightly rigged race boats for fatigue more carefully and sooner than heavily rigged cruisers.  Also, the warmer the climate, the faster stainless will fatigue, as the contribution of salt is enlarged.

“Fatigue reveals itself with cracks.  Sometimes small, “Gee-I’m-glad-I-spotted-that” cracks; sometimes “Oh-my-God-I-could-drive-a-truck-into-that-thing-and-it’s-holding-up-the-jibstay” cracks.  Sometimes the cracks have a zigzag pattern, caused by what is called stress corrosion. This can come from a combination of sources, including salt, heat, loading and from internal, literally built-in stresses like bad tempering or uneven cold-working.

“Sometimes the cracks are vertical, or radiate out from a single point.  These are usually caused by simple overloading.  Vertical cracks on swages are a common example of this; wire rope inside the swage expands with corrosion from moisture, pressing outwards on the walls of the swage until it cracks.  Some sailors try to prevent this problem by pouring oil or hot wax down their lower swages.  It doesn’t seem to make any difference, since water will migrate past anything but an adhesive put in under pressure, as one gets with Sta-Lok-type terminals.  But at least the attempt at pouring something in makes more sense than another fix I’ve seen: tightening a hose clamp around a cracked swage, to hold it together.  Not clear on the concept.
 

“Obviously it pays to invest in high-quality stainless and to make it plenty heavy, to delay the onset of fatigue.  Bronze is nearly impervious to fatigue, which is why it is so often used in toggles, turn-buckles, tangs, and chainplates.  Galvanized steel is likewise just about fatigue-proof, so if you can keep it from rusting, it will outlast stainless.  If your survey reveals broken yarns in a halyard wire, and the sheave is adequate-sized and the wire is fairly new, consider using a galvanized wire halyard.  It will require only period oiling (Marvel Mystery Oil is great), is stronger than stainless and stretches less.  Alternatively, you can increase the size of the stainless wire, but this will also involve increasing the sheave size.  Can of worms.

“When rigging wire fatigues, its strands will begin breaking.  Note that a single broken yarn in 1 x 19 wire reduces strength by more than 5 percent.  Wires will usually break first at the lower ends of standing rigging, where corrosion and fatigue work together.  But check both ends and all the wire between, just in case.  Fatigue can be reduced by increasing wire size, but again this is not always practicable, especially for racers, as it increases weight aloft. It’s usually better to use an appropriately sized wire (see “Selection Wire”, Chapter 5) and to employ other fatigue-reducing strategies.  The easiest one is the addition of toggles.  Put one at either end of each turnbuckle or buy turnbuckles with built-in toggles.  Add another toggle at the wire’s upper end, particularly on stays with sails hanked to them, as these are most heavily worked.  And keep your rigging snugly tuned so that sailing motions won’t cause your mast to bank around, shock-loading your wires". (Bo'sun Notes: Toggles are a great investment to prolong the life of your rigging. Click here for our Rigging Toggles;  Closed Body Turnbuckles: Toggle/Toggle, Swage/Toggle .

“Rigs with swaged terminals are among the most susceptible to failures; frequent inspections are necessary to ensure their integrity.  If the strands of a wire rope do not lead fairly into a swaged terminal; if there is evidence of corrosion, especially at the top of the terminal; or if the terminal is cracked or warped, no matter how slightly, it is of uncertain integrity and should be replaced at once.  Swages are the overwhelmingly favorite choice for sailboat terminals because of their low cost, neat, compact appearance and high initial tensile strength.  But they are not to be trusted.
 

“When swages fatigue, they’ll crack, too.  Again, this can also be caused by internal corrosion-the corroded wire expands, trying to split the swage apart (Figure 7-28).  Cracked swages can survive for years or days.  Replace any wire that has a cracked swage on it immediately, unless you enjoy that sort of gamble.  A horizontal crack is always more dangerous than a vertical one. Use a magnifying glass or dye penetrant to spot fine cracks.  Check the eye as well as the barrel of the fitting.  To maximize swage and wire life, consider inverting each wire when you figure it has reached its half-life, before cracks appear.  That way each end will spend some time in the clean air aloft.  And when swages are new, seal them against corrosion by melting wax down into the terminal.

“Some swages are made by a rotary swager, which hammers the fitting rapidly from all angles, making a smooth-finished surface.  If you see a lengthwise ridge on the barrel of the swage, it was formed by passing it between the dies of a Kearney swager.  Kearney swages are far more likely to crack, and frequently end up with a disquieting banana shape.  Don’t use them.

“Sta-Lok and Norseman fittings are the best mechanical terminals-right up there with splices in terms of trustworthiness.  They’re screwed onto the wire, which means there are no hammer-or die-induced stresses.   And they’re reusable, so when you re-rig you only need to buy wire, not terminals.”

“The above is by no means a complete list of things to look for, but it gives you an idea of how free-ranging and inclusive a survey mentality must be.  To give you an idea of how this might translate into reality, a sample survey follows.  It’s a bit of a flaw collage, excerpted from several vessels.  If the number and severity of flaws seem high, bear two points in mind: (1) A moderately run-down rig and one in good condition will have roughly the same number of notations; as you fix big problems, you start noting smaller ones. (2) Assuming the mast is still standing, the list of things that are okay is always longer still".