Chainplate Check
After completing our longest passage ever—3,300 miles of downwind sailing—my husband, Tom Bailey, and I anchored Oddly Enough, our Peterson 44, in a quiet cove in the Marquesas. As part of our maintenance routine, I checked the deck-level rigging before we sailed farther into the Pacific. I wasn’t expecting to find any problems—regular checks on the long passage hadn’t turned up anything—but when I got to the backstay, I found a pronounced crack in the top of the chainplate running through to the clevis pin.
Our options for replacing the chainplate were limited. A friend suggested we might use leaf springs from a big truck, which should be available even on an out island. We could then replace the mild steel with stainless steel when we returned to civilization. Luckily, there was a less-dramatic option. The chainplate extended far enough above the deck to cut off the top and drill a new hole for the clevis pin, which we could do using our boat tools and a drill press carried on board by the friendly owners of a powerboat.
Chainplates eventually fail due to the same factors that affect standing rigging: corrosion and metal fatigue. Corrosion can occur in the open air or in places—such as where the chainplate runs through the deck—from which oxygen is locked out; the latter is called anaerobic corrosion. Metal fatigue happens at the points where plates are subject to working—the side-to-side movement that leads to fracturing of the crystalline structure of the metal. Dyes are available that can be used to check for cracks, but it seems that chainplates are rarely tested and aren’t often removed for inspection.
When we bought Oddly Enough, we removed our chainplates and took them to a welder for inspection. They were in good enough shape to be used after he spot-welded a few areas of minor corrosion. Washers had been welded to our plates to increase the thickness of the top and so distribute the load on the pin. The welds probably weakened the metal and contributed to corrosion.
When we were finally berthed in a port with good marine facilities, it was time to replace all of the chainplates. To do this, first remove the shrouds and/or stays. Be sure you know what removing the stay will do to the rig. If you’re in a marina or a calm anchorage, it’s likely that a keel-stepped mast will continue to stand by itself if any of the shrouds are removed. But if you have any doubts, run a halyard to take up the strain. Before removing forestays and backstays, you must arrange backups. For the backstay, we rig a bridle to hawse holes at the stern, and we attach the main halyard to the bridle. For the forestay, you could use an inner forestay, if your boat has one, or better yet, rig a halyard and tension it to take the forestay’s place. Half a dozen turns off a turnbuckle will loosen the wire enough so that the clevis pin can be pulled out.
Remove all deck plates, and scrape away any sealant. The chainplates can then be unbolted and pulled up through the deck. Often, access to the bolts holding the plates to knees or to bulkheads is hidden behind interior furniture that must be dismantled. On Oddly Enough, we’d removed the locker linings to have ready access to the knees; this arrangement looks shippy rather than elegant, but it allows us to pull bolts to check for problems.
Chainplates mounted on the outside of the hull should also be inspected, as they, too, are subject to fatigue and corrosion, especially on the side facing the hull. Such chainplates are generally easier to remove and replace than the ones for inboard shrouds.
When you have new chainplates made, specify exactly what’s needed, especially if you’re sailing in remote areas. Rigging and fasteners may be specified in either metric or U.S. measurements, and it’s best to give sample pins and bolts to the machine shop. In our case, stainless-steel stock in a thickness appropriate for our lower shrouds was available in town, but not for our uppers or backstay; we had to pay for a sheet of stainless steel out of which the new chainplates were cut. The new plates came out beefier than the old, which was fine with me—chainplates should always be oversized—and it was easy enough to enlarge the holes in the deck. Finally, if your plates are bent, be sure to specify the angle you want or give the machinist the original to match.
Factors that lead to early chainplate failure can often be prevented. Clevis pins must be matched to hole size. A pin that’s too small causes point loading; instead of the upward pull of the rigging being distributed around the circumference of the hole, it’s concentrated on just the metal surface that touches the plate. Use either a larger pin or a bushing that narrows the hole to the proper size. The pin should fit snugly, but not so tightly that it must be hammered in.
One contributing factor to anaerobic corrosion is moisture trapped between the deck and the chainplate. Cover plates are bedded with sealant and screwed to the deck to help form a protective sealing rim around the straps. The cover plates can be pulled up, the straps inspected at deck level, and the covers resealed without removing the chainplates. Adding covers on Oddly Enough prevented the kind of minor corrosion that we’d had spot-welded.
It’s easy to ignore your chainplates and just hope they’re in good shape. Pulling chainplates as part of regular maintenance isn’t practical, but if you can get to your belowdecks fasteners, you should remove a few to check for moisture, which usually means there’s a leak at the deck level. Any corroded bolts should be replaced with new ones. It’s a good idea to mark which ones are prone to corrosion and check them occasionally. Pulling the clevis pin, a good maintenance practice, allows you to assess the condition of the top of your chainplates. A bent chainplate may crack at the bend, especially if the bend isn’t exactly in line with the pull of the stay. Any pumping of the rig will cause the chainplate to work back and forth. As the bend is usually at deck level, this makes pulling chainplate covers and digging out the sealant a critical check.
Regular maintenance of your chainplates, as with any piece of sailing gear, builds up a picture of what that equipment looks like when it’s in good shape and will aid you in recognizing when it’s time to make appropriate repairs.
