Yeah, I always thought that ship looks too big to sail. 
Also, aircraft carriers really look top heavy, but clearly the weight distribution is managed properly (USS Ronald Reagan).
There have been a few famous cases of ships too top heavy to stay upright. Exactly why the Mary Rose sank is uncertain, but top heaviness after retrofitting with more guns was probably a factor.
The Swedish ship Vasa was so unstable it capsized on its maiden voyage.
No never. seawater is never pumped into bilges for any reason. In the engine and boiler rooms it is the responsibility of the oiler to keep the bilges pumped dry when at sea. And an AB should be checking the cargo bilges to be sure they are dry. If the bilges were to have water in them as the ship rolled cargo could get wet and damaged. In the engine and boiler room if the bilges are not pumped then machinery, piping, and other equipment and structures would be subject to corrosion.
Seawater is used as ballast but is pumped into ballast tanks, not bilges.
At sea they ride the same as in port generally. The only exception would be if the vessel is going to encounter extreme weather in which case (rarely) a vessel that is lightly loaded or not carrying cargo (described as being “in ballast”) will take on more ballast to lower air draft and increase prop submersion and stability.
Saltwater washdown of holds is the only circumstance I can think of, although of course that isn’t directly to put seawater into the bilges, but that’s where it ends up.
Sure. Take a stable configuration with CoM below CoB. Then, add a small, dense weight on a very long lever arm to the side of the ship. You can generate an arbitrary amount of torque like this, so there’s some arm length where the ship will tip over.
I think Chronos might have meant a design that wasn’t quite that unstable. I.e. one that would stay upright until disturbed and then flip over, not one that can’t stay upright no matter what.
An extreme example is a floatplane (airplane with pontoons). There’s hardly any weight below the water, just empty pontoons. But they are stable, because as soon as it starts to tilt, one pontoon dips deeper into the water, shifting the center of buoyancy towards that side.
Pontoon boats are pretty top-heavy too.
The wide, boxy hulls of cargo ships and cruise ships have the same effect.
Also the South Korean Ferry the Sewol
Not about buoyancy but surely the most telling comment: “The company budget for the safety training of the crew was $2 American, which was used to buy a paper certificate”
If you ever get the chance, I highly recommend the Vasa museum in Stockholm. It is utterly fascinating, and the ship itself is gorgeous.
And to clarify a bit, “on its maiden voyage” might bring visions of capsizing somewhere out in the open sea. However, the Vasa floundered right as she left the harbor.
But that’s like 5 billion waung!
The Vasa museum in Stockholm is amazing. If you are ever in Stockholm go see it.
Also the SS Eastland.
I don’t think so. The forces want to be at equilibrium. the COB will push upward on the ship while the COM will push downward. A ship is unstable when the COB is below the COM because without enough lateral force to counter they COB and COM will try to switch places and the boat will capsize.
Marine engineering of warships in the age of sail must have been tough - the ships are made of wood and powered by tall sails, yet the heaviest things on the ship - the guns - are best put as high as possible. Instability seems to be hardwired into the very design requirements.
Yes, but take a look at this cutaway of HMS Victory. Most of the stores and the ammunition and powder magazines were below the waterline, the decks just had the guns.
But the weight on the lever will move the center of mass.
Certainly, it can be done (and was done) so that ships were stable. By the time the Victory was constructed, marine engineers had worked out just how to do it, and had been doing it for some time. Compare with the Vasa, built early in the career of multi-gundeck ships.
The Vasa also had the heavy stores in the hold, just like the Victory - but was still dangerously unstable.
The Mary Rose allegedly sank for a slightly different reason: her heavy guns were put low, but the redesign added too much weight; so when she heeled over in a wind, water came in through her gunports, sinking her. Of course, she was a much earlier design even than the Vasa, but compared with the Vasa was a much more successful ship: the Vasa sank right away, while the Mary Rose was in service for years before sinking.
I seem to recall that both in both the Aubrey and Hornblower books, gun placement is referenced many times. Heavier guns on the lower decks and smaller guns on the upper decks.
This is not true. See my post upthread in which I cite the catamaran as an example of a boat with its CoM clearly above the CoB. A roll will cause the CoB to shift laterally farther than the CoM, causing a moment that tends to roll the boat back toward vertical (see numerous links upthread explaining hull stability). There are also plenty of single-hull boats for which the CoM is above the CoB; the shape of the hull is such that a roll causes the CoM moves laterally so as to ensure stability.
Instability happens when the CoM is too far above the CoB, such that the CoB can’t move laterally far enough to counteract it.