submarines!

zanzjan said:

So, hey, if I had a submarine-like vessel, submerged but apparently physically intact, would there be a way to determine from external observation if the vessel was still full of air or had become filled with water? (setting aside the question of how or why the latter might happen and other effects that would have.)

TIA

-Zanz

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Most likely not, unless there's an open hatch or some other visual cue. If she's buttoned up and there's no apparent sign of damage you don't have many options.

dpaterso said:

When you say submerged, do you mean lying on the sea bed? That would certainly be an indication that it's full of water.

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Or the captain is attempting to use the sea floor to hide. It's a tactic called bottoming.

Buoyancy can be either positive, negative, or neutral. If something is positively buoyant, it floats. If it is negatively buoyant, it sinks to the bottom.

Neutral buoyancy is when life gets interesting and is vital to understanding submarines. As an object sinks, it may reach a point where its negative and positive buoyancy balance out and the object becomes neutrally buoyant. In other words, it will sink no further, nor will it float any higher.

So if you want to sail your submarine at a depth of 100 feet, you add extra sea water and vent air until you add enough weight to sink 100 feet but no more. At that point, adding more water and the boat sinks lower. Adding more air and the boat rises.

A submarine is designed with an inner, pressure hull and an outer hull. Water is added in the space between the inner and outer hull when the submarine wants to submerge. The pressure hull is only external in a few select locations.

Even if a submarine is sitting on the bottom and unable to get off the bottom, the inner pressure hull can still be dry, providing this has occurred above the boat's crush depth. Only way I can think of to know whether a submarine is flooded is if one of the hatches is open or there is structural damage. If the pressure hull is intact, it is unlikely that the inner hull will be flooded. Although amazingly complex, the principles for submarines are relatively straight-forward, and you'd need to present me with a very good reason for why the inner, pressure hull is flooded.

Remember that the pressure hull is designed to reach depths of a thousand feet or so, where the pressure is over 400 pounds per square inch.

Jim Clark-Dawe

I've heard of 'bottoming', and I wonder, though, if the submarine was still full of air, that an expert couldn't tell the difference between a submarine just lying on the seabed, or a sub full of water actually pressing down on the seabed?
The way a car's tires and suspension look slightly different if it's up on a lift with no pressure on them, or parked on the road with the weight of the car on them?

Does anyone know enough about submarines to tell?

frimble3 said:

I've heard of 'bottoming', and I wonder, though, if the submarine was still full of air, that an expert couldn't tell the difference between a submarine just lying on the seabed, or a sub full of water actually pressing down on the seabed?
The way a car's tires and suspension look slightly different if it's up on a lift with no pressure on them, or parked on the road with the weight of the car on them?

Does anyone know enough about submarines to tell?

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As stated elsewhere, the only way to know visually if a submarine has flooded is if there's either an open hatch, or a big gaping hole in the hull. You're not going to be able to just look at a boat otherwise and be able to tell by eyeball.

Thank you for clearing that up for me.

zanzjan said:

So, hey, if I had a submarine-like vessel, submerged but apparently physically intact, would there be a way to determine from external observation if the vessel was still full of air or had become filled with water? (setting aside the question of how or why the latter might happen and other effects that would have.)

TIA

-Zanz

Click to expand...

I know your work takes place on an alien planet, where a depth-pressure, online converter/calculator is not of use because it is gauged for Earth's conditions. You also noted that you will use modern-era technology (instead of early-era submarines), where the vehicle can withstand more pressure at depth. Like a nuclear submarine compared to a German sub seen in the movie U-571.

I'm not sure of the "submarine-like vessel." Is this like a submerged hypobaric chamber or something similar in size and physical design (that does not move)? Is this something else, like an underwater laboratory (i.e. larger)? Is it something that is designed to move (like a ROV/remotely operated vehicle) that is smaller.

If you are dealing with modern-era technology, like a nuclear submarine, and if it does not have gashes/gaping holes in the side of it and no hatches are open, I'd assume the vessel is not filled with water.

Send an ROV to investigate before going down risking life.

frimble3 said:

I've heard of 'bottoming', and I wonder, though, if the submarine was still full of air, that an expert couldn't tell the difference between a submarine just lying on the seabed, or a sub full of water actually pressing down on the seabed?
The way a car's tires and suspension look slightly different if it's up on a lift with no pressure on them, or parked on the road with the weight of the car on them?

Does anyone know enough about submarines to tell?

Click to expand...

We've got quite a few sunken submarines that have been explored. Some have been able to be entered through cracks in the hull, while others are sitting on the bottom looking like they could sail away (other than sitting on the bottom for seventy years).

The outer hulls of submarines can be substantially damaged without effecting the structural integrity of the pressure hull. And it's the outer hull that you can easily see.

Submarines are unusual when they are on the surface for the low amount of positive buoyancy that they have. If you look at a submarine on the surface, you'll see how low it is sitting in the water compared to most ships. Other than the conning tower, a submarine on the surface is just barely afloat. Thus it needs very little additional weight to sink or submerge. A submarine is actually designed to sink or submerge with the entire pressure hull still being full of air.

In DAS BOOT, at one point the U-boat is stuck on the bottom with the pressure hull in tack, but the ballast tanks were full, and there was water in the lower sections of the pressure hull. Without forcing some of that water overboard, the boat would not have gotten off the bottom.

Jim Clark-Dawe

Well, the presence of sounds from mechanical activity, like machinery, hatches opening and closing, people banging on valves, etc... would be an indication that there is still life and it the inner hull has not been flooded. The absence of such wouldn't be a confirmation either way.

You might want to read accounts on the Soviet Kursk submarine disaster. The sub was bottomed on the floor, and there is evidence that the crew survived for an extended period of time without power. Ultimately, the sub flooded out and they all died before a rescue vehicle could be arranged.