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post #16 of Old 01-22-2012
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Doug and I discussed this the other night in the chat. He was claiming that his chainplates had failed because a lack of "dynamic tuning" had caused excessive forces which exceeded the strength of the chainplates. However, by the very design and nature of chainplates, if they are intact, they essentially can not fail. Firstly, a chainplate needs to be built AT LEAST strong enough to handle the maximum righting moment of the boat. That is to say, there is no force that the wind could exert on a sail that could cause the chainplate to fail. Secondly, the chainplate should be made more strong than the shroud. While these are both "zero-tolerance failure" components, in an excessive event, you want the shroud to give before the chainplate, as that will reduce any likelihood of damage to the hull. Add in large safety factors, and it is impossible for the wind to cause a chainplate failure.

"But, that's ridiculous!" you shout while throwing empty beer bottles at me. "Chainplates fail all the time!" Well, yes, they do, and it's because they're a limited-lifespan part. You see, stainless steel has a big, and rather undetectable problem from crevice corrosion. Dave's chainplates in question were from 1975, and as I explained above, if they hadn't been corroded, they couldn't have failed. The problem is, chainplates aren't considered the same way as shrouds are as having a limited lifespan before replacement. This is problematic since crevice corrosion doesn't necessarily show outward signs of weakening before it fails. What would be a good decision, if one is set on the use of stainless as a chainplate material, is to replace it at the same time as the rest of the standing rigging. Two alternatives would be to use bronze or titanium (or some of the more advanced integral chainplate options, but I don't understand the engineering considerations behind them well enough to explain.)

The bottom line: Dynamic rig tuning might give you an extra couple of knots per day, or an extra bit of weatherliness, but it would not have prevented the failure of S/V Triumph's chainplates. Chainplates made from stainless are a limited lifespan part, and there have been a number of failures to prove this out, either replace them on a schedule, or change them out to a material with a longer service life. It's doubtful that this extra cost of replacement would even be as great as the extra cost of a dynamic tuning job, but it would provide much more security in knowing you have a "bulletproof" part.

Last edited by Landgull; 01-22-2012 at 06:00 PM.
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