Indeed. And many large ships do in fact sink in that 90-degree-list (or thereabouts) orientation.
I posted another example of a ro-ro ferry that did exactly the same thing, only this one had room to sink until submerged.
If you follow Vixen's YouTube link you can see she's finally decided to start paying attention to how actual experts reckon roll stability. It's not a super presentation, because it's a guy sort of winging it at a white board. But production values aside, he's not wrong. The cryptically-named GZ curve does indeed show that there is a critical heel angle that, if exceeded, reverses the righting moment and means the ship will inevitably continue to roll up to a certain point. This is something we've discussed many times on this thread.
What his presentation doesn't say is where it will stop rolling. A naval architect will say that at this point the ship has begun to "capsize," but Vixen keeps equivocating this with turtling. While "capsize" has a number of informal meanings, in strict naval architecture terminology it simply means any non-transient roll that renders the ship unable to be navigated. A 90° sustained roll is a capsize. If a ship's maximum recoverable roll angle is 56°, a 57° roll could be considered a capsize. Yes, "turtling" is a technical term -- it's a sustained roll of about 180°. If your sailing career began, as did mine, with sailing small dinghies, you are taught the difference between capsizing and turtling.
Vixen admits that there are a number of parameters that affect any vessel's GZ curve. This is true, but it doesn't seem that Vixen appreciates what those are or what effect they have. The instructor in her video draws a good approximation of a round sailing hull. But what about square hulls? What about draft? What about hulll depth? What about beam-to-depth ratio? All these things matter quite a bit. The instructor doesn't go into them; perhaps that's a topic for his next lecture.
Another thing the instructor doesn't go into is what happens after the critical roll angle. Naval architects are primarily concerned with keeping the ship upright. What happens farther to the right on the curve isn't that interesting to them, but for forensic engineers that's where the fun starts. The curve is defined beyond that, to be sure. Points G and B (the centers of gravity and buoyancy, respectively) don't stop existing. The question is where the next equilibrium subdomain begins. No, it's not invariably at 180°. Just under 90° is also fairly common, especially with "tall" hulls. The instructor draws what looks like a sealed hull. Those exist, to be sure. But tall, square-hulled ferries aren't they. Once you've reached a certain roll angle near the apex of the GZ curve, you'll be shipping water through openings in the deck and superstructure. Then rolling is not your problem, but rather the massive increase in flood rate.
Which leads us to the next point. The big issue in Vixen's video is that the model presented is for
intact hulls. That is, flooding changes the model, as do things like the shifting of cargo. The scenario presented is for rolling as the result of wind or wave, or, say, a turn executed too smartly. In flooding regimes, the GB distance can be reduced considerably. The model as presented doesn't accommodate the free surface effect. Presumably that's also a topic for another lecture.
Once again we see a little knowledge is a dangerous thing.
