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Is it correct to say that a submarine floats if it is below the water surface?

According to the dictionary definition, it seems to me that this is a correct way to refer to a submerged submarine.

Merriam Webster - float: to rest on the surface of or be suspended in a fluid.
Oxford - float: Be suspended freely in a liquid or gas.
Oxford - float: Move or hover slowly and lightly in a liquid or the air.

The way I understand it, in a liquid or fluid means within the medium, not on the surface.
Is this the proper meaning?

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    if it's not at the bottom of the ocean, any position above the ocean floor is "suspended" therefore yes, it floats. – SrJoven Oct 27 '14 at 4:03
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    @SrJoven, your notion is wrong. Eg: When Titanic sank, it took 10 to 15 minutes to go from the surface to the bottom. In that period it was not at the bottom of the ocean, but it wasn't floating, it was sinking. – James Waldby - jwpat7 Oct 27 '14 at 4:27
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    related Does a submarine cruise underwater or sail underwater? – Mari-Lou A Oct 27 '14 at 7:13
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    I'm confused. What's wrong with the definition you pulled out: "Be suspended freely in a liquid or gas." Suspended in liquid (ie. neither rising or sinking) is precisely what you're talking about. – Django Reinhardt Oct 27 '14 at 11:43
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    @jwpat7 Your response is misleading. The term "float" implicitly assumes a steady-state condition. Once the Titanic was done sinking, it was proud (in contact w/ the floor), and clearly not floating. – Carl Witthoft Oct 27 '14 at 11:57
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Objects under water can float, rise or sink.

This is a Galileo-type thermometer:

fluid-filled cylinders with glass fluid- and air-filled bubbles floating at different levels

Depending on the temperature of the fluid in which the sealed glass fluid containing sealed bubbles are suberged, they will either rise, sink, or float at certain levels. Per Wikipedia:

The only factor that determines whether a large object rises or falls in a particular liquid is the object's density relative to the density of the liquid. If the object is denser than the liquid then it sinks, as it is heavier than the liquid it displaces. If the object is less dense than the liquid then it begins to sink until the weight of the displaced liquid becomes equal to the object's weight; then it floats at that depth.

So, yes, a submarine floats at a certain depth in the ocean. If it is to surface, it rises, or it sinks to a lower depth. It works on Archimedes' principle:

Archimedes' principle is the law of buoyancy. It states that "any body partially or completely submerged in a fluid is buoyed up by a force equal to the weight of the fluid displaced by the body." The weight of an object acts downward, and the buoyant force provided by the displaced fluid acts upward. If these two forces are equal, the object floats. Density is defined as weight per volume. If the density of an object exceeds the density of water, the object will sink. - Office of Naval Research

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    The problem here is float has two meanings. It can be "floating on the surface" or "floating submerged in the water". To eliminate this confusion "hovering" is used also for "floating submerged in the water". – 0.. Oct 27 '14 at 16:52
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    @ermanen: Lighter-than-air craft are said to float, even though they generally don't get anywhere close to the top of the atmosphere. – supercat Oct 27 '14 at 22:24
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I don't want to detract from medica's accurate answer, except to add another point of view about the word float and then discuss the jargon of submarine operations.

First, there is room for poetic license with the word float, to the point where these uses are as natural and accurate as the precise meaning you might be looking for.

Parachutes, paper airplanes, and wind dispersed seeds all float gently to the ground, the buoyant force and fluid dynamics not quite or not always balancing the weight.

A seagull floats, wings outstretched and motionless, on the air rising over a dune. (The bird is actually sinking through the air, but, since the air is rising, it appears to be floating.)

Astronauts float in space, where there is no fluid to float in.

In the world of modern naval submarines, they have their own jargon to be precise about what they do:

  • Resting motionless at a fixed depth is hovering (used when launching a missile).

  • Traveling at a fixed depth, ascending and descending while traveling is flying.

  • Going deeper in a controlled manner is diving.

  • Going deeper without control is sinking.

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    There's also submerging and surfacing – Mari-Lou A Oct 27 '14 at 7:35
  • I would say that astronauts drift rather than float, although I guess that also refers to a fluid medium. – TylerH Oct 27 '14 at 14:10
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    Floating is used in the jargon also, if submarine is resting on the surface. In this case, it has a positive buoyancy. – 0.. Oct 27 '14 at 15:59
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    @TylerH drift suggests motion – njzk2 Oct 27 '14 at 20:15
  • @SrJoven: If it is resting submerged in the water, then it has a neutral buoyancy. If it is resting on the surface (floating on the surface), it has a positive buoyancy. You can do a research about this. – 0.. Oct 27 '14 at 23:27
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The OED has fifteen separate main meanings of the verb float, each with many sub-meanings. Only one of them, 3a, deals with an object floating on the surface of a liquid. Another (I think under '5') deals with the submarine situation. Yet others deal with such things as a parachute 'floating to the ground' i.e. floating whilst sinking.

If you are seriously interested in this the OED is worth a visit.

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A submarine operates by changing its buoyancy. If the average density of the submarine is less than that of the surrounding water it floats on the surface. To dive the submarine increases its density by taking water into buoyancy tanks. When its overall density increases above that of the water it sinks.

Once the necessary depth has been reached the vessel will adjust for neutral buoyancy, where its density is the same as the surrounding water, and then the depth can be further controlled by the horizontal equivalent of a rudder.

So submarines can float, but they can also sink and "hover" at neutral buoyancy. This latter condition can't really be called floating.

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Objects in liquids can have positive, negative or neutral buoyancy. At positive buoyancy they will float upwards, and negative buoyancy they will sink downwards, and at neutral buoyancy they will remain where they are.

A submerged submarine will be in these various states at various times. During the times it is at a steady depth it will have neutral buoyancy, and so can be said to be neither floating nor sinking.

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    Can you source float for upward buoyancy? – SrJoven Oct 27 '14 at 12:55
  • No, but I can do the reverse: according to Merriam-Webster, "buoyancy" is "the tendency of a body to float or to rise when submerged in a fluid." Underwater the term buoyancy is used in preference to words like "sink" and "float", I suppose because those terms are ambiguous once you're below the surface. – Echelon Oct 27 '14 at 15:18
  • Float or rise? The point of float is that the density underneath is the same as the density above. A ship floats on water because the density underneath it is equivalent to the density above it. In theory, it could be above the water (see dirigible or hot air balloon) but once it's at a fixed height, what's it doing (assuming it's not being self-propelled)? – SrJoven Oct 27 '14 at 16:05
  • You don't have to say "float upwards". It just floats. But it is correct that it floats when it has a positive buoyancy. – 0.. Oct 27 '14 at 16:08
  • @SrJoven: I didn't say "rise". It rests actually when it floats. – 0.. Oct 27 '14 at 16:15
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Submariners do not refer to submarines as floating. While a submarine may often be trimmed to be neutrally buoyant, it can also hold depth while under power and negatively or positively buoyant due to the dynamic pressure of water flowing over its control surfaces.

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One would not usually describe a submarine as 'floating', particularly if submerged. It could be termed to be "at sea", to be "underway" (or "under way"), or to be "making way". A couple of other suitable terms are available, depending on the situation.

More-or-less-technical terms (British English, recognised by mariners internationally due to their use in the International CollRegs, not specific to submarines):

Any sea-faring vessel that is going from one place to another is making a passage or 'passage-making'. It might also be at sea (not so much a technical term).

A seafaring vessel (of any kind) is under way (or underway) if it is:

  • not aground
  • not at anchor
  • not made fast to a dock, the shore, or other stationary object.

If it is propelled (by any means including sails or engine but not including tidal drift or wind drift) then it is making way.

So a submarine under power would be under way - if it's not under power but it's also not moored or anchored or aground then it's under way, not making way.

If it is unable to maneuver (e.g. because its means of propulsion have failed) then it is not under command. This is typically a bad thing.

If it is sitting submerged on the seabed and can't get up again then it has sunk. Best to avoid this.

International Regulations for Preventing Collisions at Sea (on Wikisource)

Use of the terms 'under way' and 'making way' defined in "Farwell's Rules of the Nautical Road"

The BBC has used "sit in waters" in a news story:

Aside from attack capabilities, it is able to sit in waters off the coast undetected, delivering the UK's special forces where needed

but I think that sounds weird (personal opinion).

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Float has two distinct, but related meanings. In fact, it is possible to see the two meanings as being (1) quite the same thing, or (2) contradictory, depending on context.

  1. To stay on the surface, as an air-filled ball or a piece of cork, even a drop (film) of oil, on a body of liquid.

  2. To keep off the bottom of a body of liquid (the surface at the bottom). Wrecked ships are "floated" (raised off the bottom of the sea) upwards in a slow and tedious process.

Yes, submarines do float, else they cannot move.

But no, submarines do not float, they would get spotted and destroyed by enemy fire.

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    a submarine that's stationary just over the bottom and has all noisy machinery turned down can be next to impossible to detect, especially by someone who doesn't have a highly accurate sonar map of the ocean floor in that area. Similar with one floating just under an inversion layer, just keeping station. – jwenting Oct 27 '14 at 13:25
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Submarines are driven by an engine and can change course. So I would not say they float, they move.

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  • they can however be stationary both on the surface and submerged, using at most pumps and propulsion systems for station keeping. – jwenting Oct 27 '14 at 9:47
  • Is that the normal movement of submarines unter water? – rogermue Oct 27 '14 at 13:20
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    depends entirely on the mission, obviously. If you're trying to stay undetected while observing something, you want to move as little as possible and make no noise. If you're going somewhere in hurry you're going to be going fast :) – jwenting Oct 27 '14 at 13:23

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