That's Not a Chainplate... THIS is a Chainplate!
08 02 2012 Posted by Daniel
chainplate |ˈCHānˌplāt| noun
A strong link or plate on the hull of a sailboat or sailing ship, to which a shroud is secured.
A relatively clean chainplate freshly removed from the deck joint.
Salt water does a pretty nasty job of corroding nearly every metal it comes into contact with sooner or later. Stainless steel, while higher up on the list of corrosion-resistant alloys, is definitely not invulnerable. Chromium oxide forms an extremely thin protective layer on the surface of the metal, and in cases where salt water is trapped against stainless steel without the ability for oxygen to get to the steel surface, this protective layer breaks down extremely quickly, allowing even stainless steel to rust away like plain iron. In particular this occurs in small crevice fractures or scratches on stainless surfaces, and because of the capillary action of the crevice, oxygen is excluded and salt water is drawn inwards, causing a continuation of the crack. This “crevice corrosion” is a key vulnerability of stainless alloys in the marine environment, and nowhere is it more dangerous, nor more likely, than at the location where a mission-critical chainplate passes through the deck of the boat on its way to a strong attachment point to the hull.
This passage is open to the seawater and salt spray on the deck side, and contains a transition between the steel and a sealing adhesive which seals the gap between the chainplate and the deck. As the boat’s hull moves under the pressure of the waves and the forces of the rigging, this adhesive bond, over time, inevitably breaks down, at first letting just the slightest amount of seawater in. If the boat is sailed frequently this may not be a serious problem for a long time, as the seawater gets squeezed out and fresh water, which does contain just enough oxygen to maintain the steel’s protection, is added. But if the boat sits for an extended period of time, or the gap is large enough that the water at the bottom, closest to the chainplate, does not get replaced nor oxygen allowed in, well, you have a recipe for a rapidly failing piece of metal whose sole purpose is to hold your mast upright. When that fails… well, it’s bad. Real bad.
I tell you this because I spent a significant amount of time, shed a significant amount of blood, and used a significant amount of curse words replacing, upgrading, and generally working hard on my boat’s chainplates to forestall this event. If the chainplates are removed, inspected, replaced as necessary, and re-sealed with fresh sealant every so often, hopefully any potential corrosion will be caught well before it is dangerous and at the very least one knows their rig is in good shape. Just like pulling the masts and checking them over when taking new ownership of a vessel, pulling the chainplates is another common and important task. It’s easier to pull the chainplates when the mast is already down and nothing is attached to them, so that is precisely what I did.
In order to get a chainplate out, not only do you unbolt it from belowdecks, but you must also cut away the sealant at the deck. Often, due to the importance of this location and the tough physical demands placed on the sealant, this is an extremely durable and tenacious adhesive. Removing it is not for the faint of heart and people have resorted to blowtorches, power tools, and other craziness. The goal is to free the chainplates and clean the hole of residual adhesive in preparation for bonding a new sealant in place after the inspection. I was fortunate, to a degree, in that the previous owner seemed to be a sensible sort and bonded the chainplates with a less-tenacious adhesive. This meant that it only took about an hour per chainplate to chisel, scrape, and hack my way through the rubbery goop to freedom, instead of a potential half-day or so. Once the chainplates were freed from their adhesive prison, I was able to clean them up and get a feel for how corroded they were.
Many of them were surprisingly clean and in good shape, and the adhesive protection the previous owner had applied looked to be professionally done and extremely durable. This gave me good confidence that this boat seals well when done right and does not wiggle and warp too much while underway.
However, there were a few chainplates where the sealant was either not done as well or an older and even less durable adhesive was used. In these cases, the chainplates were showing signs of accelerated corrosion, though none of them were anywhere (yet) close to what I would consider dangerous. It was for precisely these situations that I went to the trouble of pulling them, however.
I must go further!
Unsatisfied with simply inspecting the existing chainplates, though, I had already prepared by buying new, slightly larger stainless steel bar stock in order to accommodate some calculations I had done on potential rigging forces in extreme circumstances. These were not excessively large, but they give me a greater degree of confidence in their ability to handle edge cases such as knockdowns.
A “mill finish” rough surface on a freshly drilled chainplate. This is how they looked as I got them from the machine shop.
I had the stock chainplate hole pattern drilled in the new bar stock, and then I took to polishing the stock by hand as best as I could to remove those nasty, sneaky crevices and ensure a smooth surface for fresh adhesive to stick to.
An assortment of new chainplate stock on the box to the left, with a few old chainplates off to the right. Note the corrosion on the angle chainplate.
Putting a mirror finish on the chainplates with progressive sanding, then polishing, and finally buffing.
Please note: angle grinders, particularly those equipped with the nastier grades of grinding discs and/or heavy sanding wheels, are indiscriminate when it comes to what they are grinding, shredding, or generally destroying. This includes your fingers or other body parts. Please wear gloves when using these beasts as even the slightest contact can result in losing the skin off a knuckle for the better part of a week and suffering some intense pain as the nerves in that frequently used part of your finger regrow. This has been a safety advisory of The Oddasea Project. Thank you.
I spent nearly 8 hours standing in a shop and polishing the upper two-thirds of the chainplates until they had a literal mirror-finish to them. This reduces or eliminates the micro-cracks and crevices in the surface. Finally, a friend of mine who works with oil and gas hooked me up with a nasty acid which is specifically designed to chemically “passivate” the metal by creating a fluoride bond of some sort which is much much tougher than the chromium oxide layer to break down. This helps “seal off” any residual crevices and gives the stainless as much protection as I could afford to give it short of fancy electrochemical treatments and space-age techniques. To be honest, if I were going to go to that much trouble I would have just used titanium to begin with, as it does not have the crevice corrosion problem and is much more durable in seawater. If I ever have to replace these chainplates, I will almost certainly take a hard look at titanium.
Once the chainplates were polished and passivated, they were ready to be installed. This part was astonishingly easy compared to the trouble of pulling the old ones and fabricating the new. Besides simply applying adhesive sealant to the chainplate and the deck to fill the gap, I also cut a few layers of red SBR rubber to help provide a compression seal at the deck level. Combined with a metal cover plate which squeezes the rubber against the deck, the SBR helps provide some extra sealing and enhances the motion tolerance of the adhesive sealant, as well as protecting the sealant from UV. All of these combined will help give that joint as much possible resistance to the elements and the harsh duties of strong winds and salt water as possible.
With all the goop from the sealant going around, I didn’t break out a camera to get any photos of the final job, but if you’ll hold tight until I get around to the re-rigging and putting the masts back on, you’ll get a good shot of the final setup in context.
Let’s hope they give this girl a long and healthy life!
______/)______
Categories : Ship EquipmentA strong link or plate on the hull of a sailboat or sailing ship, to which a shroud is secured.
A relatively clean chainplate freshly removed from the deck joint.
Salt water does a pretty nasty job of corroding nearly every metal it comes into contact with sooner or later. Stainless steel, while higher up on the list of corrosion-resistant alloys, is definitely not invulnerable. Chromium oxide forms an extremely thin protective layer on the surface of the metal, and in cases where salt water is trapped against stainless steel without the ability for oxygen to get to the steel surface, this protective layer breaks down extremely quickly, allowing even stainless steel to rust away like plain iron. In particular this occurs in small crevice fractures or scratches on stainless surfaces, and because of the capillary action of the crevice, oxygen is excluded and salt water is drawn inwards, causing a continuation of the crack. This “crevice corrosion” is a key vulnerability of stainless alloys in the marine environment, and nowhere is it more dangerous, nor more likely, than at the location where a mission-critical chainplate passes through the deck of the boat on its way to a strong attachment point to the hull.
This passage is open to the seawater and salt spray on the deck side, and contains a transition between the steel and a sealing adhesive which seals the gap between the chainplate and the deck. As the boat’s hull moves under the pressure of the waves and the forces of the rigging, this adhesive bond, over time, inevitably breaks down, at first letting just the slightest amount of seawater in. If the boat is sailed frequently this may not be a serious problem for a long time, as the seawater gets squeezed out and fresh water, which does contain just enough oxygen to maintain the steel’s protection, is added. But if the boat sits for an extended period of time, or the gap is large enough that the water at the bottom, closest to the chainplate, does not get replaced nor oxygen allowed in, well, you have a recipe for a rapidly failing piece of metal whose sole purpose is to hold your mast upright. When that fails… well, it’s bad. Real bad.
I tell you this because I spent a significant amount of time, shed a significant amount of blood, and used a significant amount of curse words replacing, upgrading, and generally working hard on my boat’s chainplates to forestall this event. If the chainplates are removed, inspected, replaced as necessary, and re-sealed with fresh sealant every so often, hopefully any potential corrosion will be caught well before it is dangerous and at the very least one knows their rig is in good shape. Just like pulling the masts and checking them over when taking new ownership of a vessel, pulling the chainplates is another common and important task. It’s easier to pull the chainplates when the mast is already down and nothing is attached to them, so that is precisely what I did.
In order to get a chainplate out, not only do you unbolt it from belowdecks, but you must also cut away the sealant at the deck. Often, due to the importance of this location and the tough physical demands placed on the sealant, this is an extremely durable and tenacious adhesive. Removing it is not for the faint of heart and people have resorted to blowtorches, power tools, and other craziness. The goal is to free the chainplates and clean the hole of residual adhesive in preparation for bonding a new sealant in place after the inspection. I was fortunate, to a degree, in that the previous owner seemed to be a sensible sort and bonded the chainplates with a less-tenacious adhesive. This meant that it only took about an hour per chainplate to chisel, scrape, and hack my way through the rubbery goop to freedom, instead of a potential half-day or so. Once the chainplates were freed from their adhesive prison, I was able to clean them up and get a feel for how corroded they were.
Many of them were surprisingly clean and in good shape, and the adhesive protection the previous owner had applied looked to be professionally done and extremely durable. This gave me good confidence that this boat seals well when done right and does not wiggle and warp too much while underway.
However, there were a few chainplates where the sealant was either not done as well or an older and even less durable adhesive was used. In these cases, the chainplates were showing signs of accelerated corrosion, though none of them were anywhere (yet) close to what I would consider dangerous. It was for precisely these situations that I went to the trouble of pulling them, however.
I must go further!
Unsatisfied with simply inspecting the existing chainplates, though, I had already prepared by buying new, slightly larger stainless steel bar stock in order to accommodate some calculations I had done on potential rigging forces in extreme circumstances. These were not excessively large, but they give me a greater degree of confidence in their ability to handle edge cases such as knockdowns.
A “mill finish” rough surface on a freshly drilled chainplate. This is how they looked as I got them from the machine shop.
I had the stock chainplate hole pattern drilled in the new bar stock, and then I took to polishing the stock by hand as best as I could to remove those nasty, sneaky crevices and ensure a smooth surface for fresh adhesive to stick to.
An assortment of new chainplate stock on the box to the left, with a few old chainplates off to the right. Note the corrosion on the angle chainplate.
Putting a mirror finish on the chainplates with progressive sanding, then polishing, and finally buffing.
Please note: angle grinders, particularly those equipped with the nastier grades of grinding discs and/or heavy sanding wheels, are indiscriminate when it comes to what they are grinding, shredding, or generally destroying. This includes your fingers or other body parts. Please wear gloves when using these beasts as even the slightest contact can result in losing the skin off a knuckle for the better part of a week and suffering some intense pain as the nerves in that frequently used part of your finger regrow. This has been a safety advisory of The Oddasea Project. Thank you.
I spent nearly 8 hours standing in a shop and polishing the upper two-thirds of the chainplates until they had a literal mirror-finish to them. This reduces or eliminates the micro-cracks and crevices in the surface. Finally, a friend of mine who works with oil and gas hooked me up with a nasty acid which is specifically designed to chemically “passivate” the metal by creating a fluoride bond of some sort which is much much tougher than the chromium oxide layer to break down. This helps “seal off” any residual crevices and gives the stainless as much protection as I could afford to give it short of fancy electrochemical treatments and space-age techniques. To be honest, if I were going to go to that much trouble I would have just used titanium to begin with, as it does not have the crevice corrosion problem and is much more durable in seawater. If I ever have to replace these chainplates, I will almost certainly take a hard look at titanium.
Once the chainplates were polished and passivated, they were ready to be installed. This part was astonishingly easy compared to the trouble of pulling the old ones and fabricating the new. Besides simply applying adhesive sealant to the chainplate and the deck to fill the gap, I also cut a few layers of red SBR rubber to help provide a compression seal at the deck level. Combined with a metal cover plate which squeezes the rubber against the deck, the SBR helps provide some extra sealing and enhances the motion tolerance of the adhesive sealant, as well as protecting the sealant from UV. All of these combined will help give that joint as much possible resistance to the elements and the harsh duties of strong winds and salt water as possible.
With all the goop from the sealant going around, I didn’t break out a camera to get any photos of the final job, but if you’ll hold tight until I get around to the re-rigging and putting the masts back on, you’ll get a good shot of the final setup in context.
Let’s hope they give this girl a long and healthy life!
______/)______
