Along with fiberglass, stainless steel has revolutionized boat-building. This durable, rust-resistant metal is used for rigging wire, terminals, and an endless array of marine applications—but smart mariners understand its limitations. All grades of stainless are not created equal, and stainless steel doesn’t last forever. Here are a few important facts about stainless steel:
Chainplates: Grades of Stainless Steel
1. Stainless steel comes in numbered grades; the two most common are 316 and 304. When sourcing metal, make sure you get 316 or higher—and make sure your source is honest; 304 stainless looks identical to 316, but the higher grades are far more corrosion resistant. If you have deep enough pockets to afford stainless anchor chain, look for grade 318L. “Cheaper” (a relative term when it comes to stainless) chain is prone to weak welds on the links—and if the chain and anchor are submerged for any length of time, use stainless shackles, swivels, and anchors to avoid electrolytic corrosion between dissimilar metals. A stainless steel ground tackle setup is great to have, but it’s an expensive luxury.
Chainplates Need Oxygen
2. Stainless does best in the open air where it can “breathe.” Take the chainplates on my 1961 Pearson for example. The parts above deck looked fine as they were exposed to the open air, but the parts below deck—bolted into a sealed fiberglass envelope tabbed to the hull—were invisibly crystalizing. One day (fortunately while the boat was not being sailed), the starboard upper shroud exploded. An excavation revealed the mess you see below:
These chainplates did their job dutifully for over 50 years, but given their importance, consider replacing them every 30 years—just to be safe. That’s not exactly a demanding maintenance schedule.
One way to determine whether your chainplates have crystallized is to give them a firm rap with a hammer. If they’re brittle, they’ll most likely shatter, especially if they’re under pressure. If you have a shroud attached, be sure to tie off the turnbuckle to avoid unintentionally eating it if the chainplate gives way.
Chainplates: Look for Rust
3. Look for any rust or discoloration. Stainless parts are sometimes fabricated with impurities in the metal. If your terminals are all shiny except for one brownish one, don’t assume the problem is cosmetic. That terminal is rusting for a reason. Replace it.
Chainplates: Passivate Stainless Steel
4. When replacing chainplates or any stainless steel parts, be sure to passivate the metal. Like many metals (bronze, for example), a thin patina of oxidation on the surface helps resist corrosion. When you drill fresh holes in stainless stock, the newly exposed stainless surface can be compromised by ferrous material from the drill bit. Passivating agents based on citric acid are available affordably in a plastic spray bottle. After cleaning out the newly-drilled bolt holes, spray the metal thoroughly and allow it to air-dry for at least 30 minutes before installing the new chainplates. This simple step increases the life of your hardware and, if you’re stainless-aware, it will increase your confidence that your mast will stay upright.
Stainless steel is a remarkable and virtually indestructible material. Understand its limitations, grades, and lifespan for safer sailing.