Picture this: at the beginning of the 20th century, the head of an engineering firm comes into the lab, to see his chief researcher. We’ll call him Leon Guillet.*
“Leon,” says the boss, “I’d like you to invent the worst possible material to make sailboat chainplates out of.”
“An interesting challenge,” says Leon. “I think we would want something that corrodes when wet, but doesn’t actually rust. That way it would be hard to spot.”
“Ah, but what if we could make it corrode only where it is covered. That would make it almost impossible to inspect.”
“Excellent. Anything else?”
Let’s see, says Leon, “yes, it would actually get stronger, not weaker, as it ages, so that the crew would be lulled into a false sense of security. But all that time it would be getting more and more brittle, so that when it failed, it would fail catastrophically.”
“Wow, devious,” says the boss. “Get right on it.”
So Leon goes to work, and some time later he comes up, of course, with stainless steel, which nearly all chainplates are made of, to this day. Granted, it has virtues: it doesn’t corrode by oxidation in the way that mild steel does, so it can last longer. The parts that are exposed to air maintain a protective oxide coating, which is why other components of the rig tend to last more reliably. And it’s shiny, so sailors, who are much like magpies in this regard, are instinctively drawn to it. And it is cheaper than bronze. But that’s about it. Which is why chainplate failure is, and has been for some time, the leading cause of dismastings.
Most of these dismastings go unremarked, except by those directly involved. Occasionally, though, an article shows up in a sailing magazine about how some intrepid sailor deals with a dismasting. That happened recently, in an article in Cruising World. Because that article is still in the news, I will note here that the analysis of the cause of the dismasting seemed to indicate that the problem was that reinforcing washers had been welded on in the way of the turnbuckle clevis pin holes, and that crevice corrosion resulted, which led to the failure. It would be more accurate to say that someone did a lousy job of welding those washers on; a good job would not have allowed water intrusion. But even had that happened, the boat might eventually have lost its rig from crevice corrosion (typically accompanied by other types of corrosion) in other hidden spaces, most notably where the chainplate passes through the deck.
All of you people with external chainplates, stop being so smug; the part that lays against the hull can readily trap water, as can the throughbolts.
- Because of these problems with stainless, we recommend that our clients pull and inspect any chainplates that haven’t been out of the boat in ten years or so. Even sooner if the boat’s been South, or if there is any evidence of water intrusion belowdecks.
- We also recommend that, if you install stainless chainplates, you make them out of 316L stainless, polished (not electropolished) to a mirror finish. The idea is to make a low-corrosion material as smooth as possible, leaving less surface area and flaws for corrosion to propagate in.
An even better alternative is to make your chainplates out of titanium. That’s right, titanium. Over the last few years, prices for this amazing stuff have come way down, making it competitive with stainless. And the metal is amazingly corrosion- and fatigue-resistant. Crevice corrosion simply does not occur. The only question, to my mind, is which grade to use. There are several, just like with stainless, but the only two we generally care about are type two and type five.
The former is significantly weaker than stainless, and the latter immensely stronger. As you might expect, people tend to go with the latter, but it is pretty straightforward to compensate with larger scantlings, if you want to use type two. Just make sure you won’t have to re-engineer the holes in your deck to accommodate things.
One other virtue of the stuff: most people are still under the impression that this metal is still fabulously expensive. So during a suitable get-together on the dock, you get to mention, in an offhand way that you have titanium chainplates. Plus, it is shiny.
*Leon Guillet was the real name of an engineer who made major contributions to the development of stainless steel, but probably with different goals in mind.
Brion Toss is an expert on yacht rigging, blending the ageless wisdom of traditional rigging with the materials and applications of modern day. His last book, The Complete Rigger’s Apprentice is a classic. briontoss.com.