There's no point telling what the book is about, because the whole thing is too unlikely. But the Spouse saw a documentary on the subject, which was excellent, and my response to hearing about a great narrative is always to read a book. And then, there's nothing like reading about a shipwreck to put your own troubles into perspective.
So, seventeenth-century shipwreck off the coast of Australia turns into a scenario that makes Lord of the Flies look civilized. Read it because Dash gives you enough of the background to place the historical events into context. Read it because the whole time you'll be yelling out "no WAY." If you read this first you'd understand why the European stories of the day were full of unlikely incidents and implausible timing. The subtitle points to the narrative focus and I disagree with the author's conclusion of "mad", but at least they're upfront about the body count.
When they say "worse things happen at sea" I always thought the meant slowly starving as a castaway on a desert isle, I never realized it was in reference to other people. Way.