chainplate calculations for a jordan drogue

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That's great! Yes, the cleat fasteners are 1/4". Unfortunately, there is no backing plate under the cleats, but the pad-eye has a SS backing plate of about 1/8" in thickness and 2.5" diameter.

From the Crosby specs for 209A shackles:

Maximum Proof Load is 2 times the Working Load Limit (metric tons). Minimum Ultimate Load is 4.5 times the Working Load Limit based on metric tons.

So the limits on the 7/16 209A Crosby shackle (1/2" pin) would be:

WLL: 2.7 tons ~= 6,000 lbs
Proof load: 5.4 tons ~= 12,000 lbs
Breaking load: 12 tons ~= 27,000 lbs

The jordan drogue specs call for 5/8" double braid nylon to be used as a bridle and lead line.

Not sure about the safety margin... Does the 3:1 safety margin mean that each part is designed to handle 3x maximum drogue load on the system? In this case, I doubt that the topsides or deck will hold 18,000 lbs. Is it worth considering a load greater than the boat's displacement or design a system around once in a lifetime occurrence?

Just wondering... To me, it looks like the cleats will hold with a pad-eye as a backup in all, but the most dire events, in which case something else fails before the cleats will. But it's still worth considering chainplates to avoid chafing, which, people say, can be huge in severe storm conditions.

Am I wrong? I'm curious how chainplates and rigging are usually designed.

Thank you!
Gleb