You'd be right if the cavity is only compressing other organs inside the body without changing the overall volume, but I don't know why you seem to insist on making that assumption.

I thought it would be clear from my original description, via the analogy with lungs, that the cavity would not squish the internal organs but rather expand the overall volume of the body.

[–] abfarid@startrek.website 1 points 5 months ago* (last edited 5 months ago) (8 children)

I made that assumption because lungs aren't really inside, they are pretty close to the surface, so they are easy to expand. If they were inside, they would have to push other organs away.
And regarding increasing the overall volume of the body, I addressed that in another comment. Basically, Godzilla would have to visibly swell by a lot, to have that much buoyancy.
It could be that the swelling is only in the underwater part, but then Godzilla would tip over with any slight movement, because the center of mass would be way above water.

[–] snooggums@midwest.social 1 points 5 months ago (5 children)

Ducks and other waterfowl have the majority of their weight above the waterline. So do boats.

[–] abfarid@startrek.website 1 points 5 months ago (2 children)

Yes, but birds are very light in general. Most of their volume is feathers and they have a low bone density to boot. As the result, they have a very hard time diving, and have to either dive at high speed or paddle really hard to stay underwater.

And regarding boats, it depends. Do you mean completely empty passenger boats? Then yes, their density is very low by design, because they are mostly empty on the inside. When fully loaded, a commercial cargo vessel, is 80-90% under water.

[–] 5C5C5C@programming.dev 3 points 5 months ago (1 children)

You can't prove that Godzilla's bones aren't hollow ballast tanks that can be emptied and filled as needed.

[–] abfarid@startrek.website 2 points 5 months ago

I can't, and I wasn't going to. My argument was never about what Godzilla can or can't do, it was about physics. Specifically, that you can't move stuff around internally, without changing volume significantly, to change buoyancy.

Deballasting bone cavities is definitely an option. But to achieve the levels of buoyancy displayed by Godzilla, they'd need to be truly massive. Or he's using paddling in tandem to help itself stay above water, akin to what dolphins do to hold most of their body above water.

Also, you can't squeeze bones, so Godzilla needs an organ that would force discharge that ballast. Like sacks of highly compressed air, which are used to push out the water completely. This is similar to what submarines do.

Instead of bones, we could also just use your approach with organs. Emptying sacks of water and filling them with air. But either way, we need to discharge ballast, as I was saying originally. It's a limitation of law of physics, and not a limitation of Godzilla's abilities.

Source: I have a bachelor's degree in Maritime Transportation and Navigation. Which is basically a BSc on "how to buoyancy right".

[–] snooggums@midwest.social 0 points 5 months ago (1 children)

When fully loaded, a commercial cargo vessel, is 80-90% under water.

Hahaha, no.

While I can't find a comparable article for cargo ships, cruise ships are 10% underwater. A fully loaded cargo ship can't be more than 30% as they tend to be stacked far higher than the ship's sides. Ocean waves would easily swamp a ship that was 80-90% underwater.

[–] abfarid@startrek.website 2 points 5 months ago

Don't know what to tell you, man. You sound very confident, but I literally have a bachelor’s degree in Maritime Transportation and Navigation, and have served on several cargo vessels, as well as a couple of passenger ferries. I might have exaggerated with 90%, I'll give you that, so take it down to 80%.

cruise ships are 10% underwater

As I said, those are usually mostly above water, to prioritize comfort. But even those are at least 30% underwater, with very low center of gravity. You can't have a ship 90% above water; it would keel over. Except some heavyweight barges that have big surface area, I suppose.

A fully loaded cargo ship can’t be more than 30%

In fact, that's about the least an empty cargo ship is underwater. Because when empty, cargo ships take ballast to prevent capsizing. Also the propeller is designed to be at least a few meters below water to be effective.

they tend to be stacked far higher than the ship’s sides

I think you're focused specifically on container vessels. Those still have way more massive holds than the containers you see on deck.

Ocean waves would easily swamp a ship that was 80-90% underwater

Depending on the season and projected weather conditions, ships are leaded to a different extents. They have load lines for winter and summer. In summer, for certain cargo ships, the freeboard can sometimes be measured in centiliters. I remember being able to kneel on deck and reach the water with my hand. In heavy seas, the waves are constantly on the deck and the ship can handle it fine; you just don't go there.

Ships often look deceptive about their draft, because you almost never see a ship truly empty. Even when not carrying load, they have a lot of ballast.

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