The chainplate is typically a metal plate used to fasten a stay to the boat. One end of the chainplate has a hole for the pin of the turnbuckle, the remainder of the chainplate is used to attach the plate to the boat via a bulkhead, knee, tie rod or the hull itself. Chainplates get their name from the old wooden ships that used to use three strand tarred manila or hemp rope (instead of wire) in conjunction with dead eyes and lanyards to tension the rigging. The dead eye would be attached to a chain or a link which would be connected to a plate that was fastened to the hull. This plate was called the chain plate.
Modern day chain plates are typically made of stainless steel and sometimes aluminum. When replacing a boat’s standing rigging one should also be sure to, remove, inspect, clean up and refasten the chainplate. Apart from design and material flaws there are three primary factors in the life expectancy of any chainplate: fatigue, age, and corrosion. One of the common misperceptions of stainless steel is that it does not rust. Depending on its grade, stainless steel is very resistant to rusting, but will rust and may do so prematurely without the presence of the oxygen molecule. This in-itself presents a problem when sealing a chainplate to the deck or the hull in effort to keep water out. Chainplates that are mounted through the deck are the most suspect because they are prone to suffering from crevice corrosion mostly due to the seal created at the deck. Again, this is due to the lack of oxygen which is typically supplied by water or air. This can create an area of concern mainly due to the fact that it is right in-between the two pulling forces of the plate, i.e. the top bolt hole and the hole that accepts the pin for the stay’s turnbuckle. Through-deck chainplates are susceptible to failure because of this if not inspected regularly.
This brings me to the cover plate that mounts horizontally onto the deck. The chainplate cover plate is there to merely promote a seal. It is not structural, does not need to be through-bolted, and should be lifted, cleaned, and resealed every two to three years (give or take) depending on geographical location and use. This is both to preserve the decks core materials as well as keeping water out from below decks (Read our blog here on sealants and their uses).
Deck mounted chainplates will typically have few issues with failure within the actual plate (again, this is aside from fatigue, design and/or manufacturing flaws of course). The fasteners in this case are taking the ‘ brunt of it’ and care should be taken to ensure that the fasteners and/ or any associated tie-rods are in optimal condition. When removing the stainless steel fasteners you will see evidence of rust where they go through the deck. These types of chainplates should be resealed and have the fasteners replaced regularly (about every five to seven years, depending on use and geographical location).
U-bolt style chainplates, should also be pulled, inspected and re-sealed regularly. These types of chainplates should be replaced more frequently than the other styles. This is due to the fact that they depend solely on the threads used to fasten them through the deck.
So when do you need to replace your chainplates altogether? Replacing chainplates should be done if there is damage or evidence of cracking. Unless there is clear evidence of impact, one should replace ALL of the boat’s chainplates if there are signs of wear or damage on any one of them. Extreme age (30 + years, again depending on geographical region and use) can also be a factor for replacement. In terms of fatigue; if a boat has been sailed hard for many, many miles, i.e. a circumnavigation, one should consider having new chainplates made before setting off again. The quality of the stainless used is an important consideration as well. Many Taiwanese and some Floridian manufacturers, amongst others, are notorious for using sub-marine-grade stainless steel for their chainplates. The life expectancy for these low grade metals cannot be estimated in a marine environment and should therefore be replaced as soon as possible!
In conclusion, chainplates are an often overlooked portion of ones rigging. I have even witnessed rigging shops that neglect to inform customers of the importance of chainplate inspection. If in doubt of your chainplate’s state, it is, at the very least it is a good idea to have them removed, cleaned up and inspected by a professional. If you are a do it yourself-er, there is no shame in seeking advice, not just for removal but most importantly for inspecting them as well as tips on installing them properly. So if you are having your boat re-rigged, be sure to ask about those chainplates.