Pretty scarry to do a "Chinese gybe" and have the boom rise-up and slam the backstay!

Did the preventer line break, or the boom fitting, or?

Where on the deck was the end sheeted-vang secured?

How far out was the main before the unexpected gybe? 60° from amidship's?

As I recall you don't have a vang on Christmas.?

Oh, and, What was the water intrusion from?

By the way, since my experience is as a "seasonal cruiser" in the Gulf of Maine (and even Cape Cod Bay), I've found yours and Todd Dunn's decsriptions of conditions instructional :^)).