Doug I feel your frustration. I hate it when experts disagree.
I have a mental picture of what happened, let me know how accurate it is.
The shrouds were a little loose. The wind picks up and the top of the mast is whipping around more than it should. Maybe the top of the mast moving a foot out of column from where it should be. The mast is lets say about 60 feet tall. The top is a foot or two out of column. How much does that affect the angle of the shroud between the deck and the shroud. Maybe one degree.
So the theory that the chain plates were damaged by loading in one storm does not make any sense to me at all.
The place that they broke is exactly where they would be expected to break if they had oxygen depletion corrosion.
Now the mast whipping around certainly didn't help but there was another thread where someone gave his old chain plates to a friend with a machine shop to use for scrap metal because they looked perfect. A few months later the machine shop guy tried to cut one in a shear. It shattered and crumbled.
My son is a rigger in Annapolis and I asked him about this a long time ago. His response was that if you are going to go to the trouble and labor to remove and re-bed then he would never even consider not replacing them.
Of course at rigging shop rates it is a no-brainer but even for do-it yourselfers chain plates are not forever.
I would submit that if there is anyway you can damage a chain-plate by pulling in any direction that is generally up with the wire shroud meant to be attached to it, the chain plate is not properly designed or is damaged.
The chain plate should be able to handle much more than the wire.
Well, we stepped the main a little less than a year before the failure. Right after reinstalling the main, we tightened / adjusted the stays / shrouds at the dock, then we sailed from Fort Lauderdale to Boston. Then I checked the tension, and I did have to tighten the backstays.
A few day sails.... winter ..... spring, then we headed to Europe.
I was not aware of any main mast movement, at any time. From what I was told, there is this harmonic vibration condition which can occur wherein the mast might "pump" (fore and aftward) but almost imperceptibly. And, this occurs when the rig is not properly adjusted, specifically if you don't do the follow up / at sea / under load adjustments.
Considering the perpendicular juxtaposition of the chainplate tabs to the hull, i.e., the tabs' flat width was in the port / starboard plane, if the stays were pulling fore and aftward, then those tabs would have been stressed in their weakest direction..... theoretically.... :-)
However, I could never argue that these chainplates weren't quite probably well past their prime.
Is it just sort of coincidental(?) that fairly soon after the stepping project, the chainplates failed, especially after not doing the full re-installation process?
Imagine getting years out of a motor, incident free, and then after changing the timing chain, surprisingly enough, the motor throws a rod....
I guess this old codger is stuck in that sort of mind set.
Everything was fine until......................
Nevertheless, I suppose, (and following your later comment) BOTH issues were in play. The chainplates were old, AND I had not properly adjusted the rig after the stepping of the main.
I WILL be buying a guage and will be using this thread to try to address this issue as soon as we get a sailboat. And boy I sure do hope that is soon. :-)