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This is a follow-on to my note from yesterday on metacentric height (referred to as "GM" among naval architects) and its effect on gunnery.
Consider this a second short primer on the subject.
The standard relationship is basically: Larger metacentric height (GM) = larger Righting Arm (RA) = greater stability As I mentioned before, GM is a design characteristic of ships.
A ship impacted by external forces basically behaves as a pendulum of length GM.
The NTB-630 was more heavily armed and armored than its close cousin, the ARC-170 starfighter, and the similar PTB-625 planetary bomber.
The NTB-630 was created to deliver its payloads while engaged in space battles, and was therefore also more maneuverable than the PTB-625, allowing it to get close to capital ships and avoid their turbolasers as it executed bombing runs.
COM)), who is a Qualified US Navy Chief Engineer and Former Damage Control Officer, USS Arkansas.
While conventional thinking leads to the belief that any amount of flooding below a ship's center of gravity is good, in reality this is only true if the compartment in question is COMPLETELY filled, for any partially filled space -- regardless of where it is located -- will lower a ship's stability through what is known as the free surface effect, which has a severe negative impact on the size of the GM (clearly, any flooding above a ship's center of gravity is BAD).
I hope that this note helps people achieve some more understanding on this somewhat arcane topic!
Just a quick comment: there is no explicit relationship between a ship's stability and its inherent buoyancy - HOWEVER, as weight is added to a vessel (either deliberately through periodic updating or conversion, or inadvertently as a result of flooding from battle damage) this situation will tend to reduce the ship's design RA curve (the plot of the magnitude of righting moment versus the ship's angle of heel or list) which is considered to be the best indicator of stability.
As a sinking ship fills up more and more with water, her effective displacement goes up and her metacentric height goes down.
This results in her roll period getting longer and longer, and she tends to feel increasingly "loggy" (meaning that her RA is getting smaller and smaller, therefore reducing her ability to right herself) -- until the final catastrophic moment arrives when she rolls completely over and doesn't recover.