# Can any manmade vessels float on ocean of liquid nitrogen?

Humanity is finally reaching the interstellar space and had discovered a terrestrial planet covered in liquid nitrogen, the planet is orbiting a star thrice as massive as Sun but is too further away to produce liquid water for life. I am wondering is there anything we build that can sail on such an ocean for hours?

P.S: When the starlight shines on the surface of the ocean despite being so far out it can create a geyser effect that blows up tons of liquid nitrogen into the upper atmosphere! Yup it's that volatile and this is based on actual events on one of the Moon in our solar system.

Inspired by Nitrogen geyser and the energy from the star allows it to split heaven!

• Some questions, 1 are there any limits on building materials, 2 is there any wind, 3 can humans be above deck. Jan 29 at 6:18
• Could you please give a cite for "light shines on the surface of the ocean despite being so far out it can create a geyser effect that blows up tons of liquid nitrogen into the upper atmosphere"? This would violate several laws of physics, so I think you are misinterpreting something. Jan 29 at 6:24
• What atmosphere are you postulating for your planet? Only hydrogen and helium would be gaseous at LN temperatures; oxygen, nitrogen, ammonia, methane, fluorine, the noble gases other than helium, would all be liquid. Some of them would float on the LN so you're going to have to eliminate them from the planet if the ocean's surface is to be LN. And if the vessel generates any heat (from occupants or electronics) and allows it to conduct through the hull, you'll vaporize a layer of nitrogen and the vessel will sink more deeply.
– CCTO
Jan 29 at 14:57
• Nothing in your cited article, or en.wikipedia.org/wiki/Cryovolcano or en.wikipedia.org/wiki/Doom_Mons. The hypothesized causes are tidal friction and radioactive decay. Jan 30 at 1:24
• @TMN: Most boats would probably float on liquid N2 - density 0.808 vs 1.0 for H20. You would just be able to load less cargo before reaching the Plimsoll line: oceanservice.noaa.gov/facts/plimsoll-line.html There are material questions: would common materials become brittle from the extreme cold, or possibly react with the N2? Jan 30 at 18:20

Density of liquid nitrogen at 1 bar and 79 K is about 798 $$g/l$$. For comparison water is 1000 $$g/l$$.

When compared with water a boat would sink about a 20% more once put in liquid nitrogen, but unless it has been designed like the Vasa it should float.

Of course be sure that it is properly insulated: you don't want to be stuck wherever you happen to touch some cold surface with your bare skin.

What would it be like to navigate a rowboat through a lake of liquid nitrogen?

Liquid nitrogen is very cold.

Liquid helium is colder, but they're both closer to absolute zero than to the coldest temperatures in Antarctica, so to someone floating on them in a boat, the temperature difference is not that significant.

Liquid nitrogen has a density similar to that of water, so a rowboat would float on it, but if you were in it, you wouldn't survive for long.

If the air above the nitrogen was room temperature when you started, it would cool rapidly, and you and the boat would be smothered in a thick fog as the water condensed out of the air. (This is the same effect that causes steam when you pour out liquid nitrogen.) The condensation would freeze, quickly covering your boat in a layer of frost.

The warm air would cause the nitrogen on the surface to evaporate. This would displace the oxygen over the lake, causing you to asphyxiate.

If the air (or the nitrogen) were both cold enough to avoid evaporation, you would instead develop hypothermia and die of exposure.

• Whatever you do, don't try to lick the mast with your tongue. Jan 29 at 10:00
• Good example, but there probably wouldn't be much cold issue, since for the nitrogen sea to form, it would already be super-cold and there would be no water in the air. Jan 29 at 13:52
• The boat would also skip over the surface for a while as it causes the nitrogen in contact with it to boil instantly, forming a thin nitrogen gas layer around it.
– Yakk
Jan 29 at 15:37
• @Yakk I don't think so, unless it's very light. The outside will cool down to liquid nitrogen temperature. Jan 29 at 18:33
• @user253751: That's where the "for a while" comes in - the Leidenfrost effect can only create a layer of gas insulation until the boat cools to closer to the boiling point of the LN2. Jan 30 at 6:48

# Probably yes

Things are buoyant if they can displace water (or, liquid) equivalent to their own weight (well, mass, but I'm not doing the science hard enough and don't want to suggest that I am). Specifically:

In simple terms, [Archimedes'] principle states that the buoyancy force on an object is equal to the weight of the fluid displaced by the object, or the density of the fluid multiplied by the submerged volume times the gravitational acceleration, g.

Wikipedia says that liquid nitrogen ("LN2") has 80.8% the density of liquid water. I'm not an expert, but that doesn't seem like a big enough difference to make it impossible for a vessel to displace its own weight. The Wikipedia article for buoyancy even has a photo of a coin floating on liquid mercury.

I'd guess that vessels built to sail on LN2 would probably be wider than ocean vessels. My intuition is that this increases the surface volume of the vessel relative to its mass, increasing its buoyancy to counteract the weaker upthrust from the less-dense LN2.

NuclearHoagie addresses the general problem directly and more succinctly:

It's never impossible for a vessel to displace its own weight in fluid, you just need to make it big enough... This is totally feasible, as the weight of the boat is mostly related to its surface area, which increases more slowly than the volume due to the square-cube law.

("NuclearHoagie" is a submariner's handle if ever I saw one, and buoyancy is a core concept for anyone who lives in an underwater metal tube filled with atmosphere.)

Of course, let's not forget that LN2 is pretty cold stuff. That is going to pose some fun engineering problems when it comes to the hull, and to locomotion. If the planet has no atmosphere, any sailing vessel will need to generate thrust by interacting with the liquid. That could mean oars, or a turbine. Or, because LN2 is so cold, perhaps a small heat source aft could generate thrust by causing rapid, localized expansion of the LN2 to push the vessel forward.

ETA: I think the temperature thing is going to be a huge deal. Sailing on an ocean of cryogenic fluid is going to pose unique problems that will definitely kill your passengers and destroy the boat, even if it continues to float.

Wikipedia says LN2 clocks in at -196 C, which is fantastically cold. Why is this a problem? Space is cold, so why isn't it a problem in space?

Consider wind-chill. If the air flowing past you is colder than your body, it will carry heat away from the surface of your body. The reason it feels colder when the winder is stronger is because stronger wind is just a greater quantity of atmosphere whipping past you per unit of time, which means more atmosphere to carry heat away from you faster. If the air temperature is 0 C, powerful winds can't cool you to below 0 C, but they will cool you to 0 C faster than if there was no wind.

Yes, space is cold, but space is also a vacuum, which is just to say: there is no stuff floating around in space that can absorb your heat energy. So, you'll eventually freeze in space, but it will take a long time. Long enough that we can easily counteract it with insulation and conventional heat sources. (And, also, humans in space do float around because they are weightless. That doesn't make them immune, but it does mean the air inside the spaceship helps shield them.)

Wind is just atmosphere in motion. Atmosphere is just very thin soup. Ocean is very thick soup. An ocean of LN2 is pretty thick soup that is also stupendously cold. If the vessel is not moving, the LN2 it's touching will absorb some heat from the ship and warm up. As it warms, it will absorb additional heat more slowly, until it reaches equilibrium with the hull. (Or, until the LN2 undergoes a phase change, but let's ignore that and pretend the LN2 will magically stay liquid no matter its temperature.) If the vessel is moving, it will continuously move away from the warmer LN2 and come into contact with LN2 that hasn't been warmed yet. It's the same principle as wind-chill. If the vessel is moving faster, that means more LN2 is flowing past the hull per unit of time, carrying heat away from the hull faster.

An ocean of LN2 is essentially a bottomless energy-void that craves heat. It will relentless drain all the energy out of the vessel. The faster the vessel moves, the greater the drain. First, the hull will be cooled down to -196 C. That will happen very fast. Then, anything in direct contact with the hull will be chilled to -196 C, and so on and so forth, until every object is frozen solid that is being held aloft by the hull.

So, where is your human passenger? Sitting on a cushion on a wooden chair with rubber feet, on the floor of the bridge? Where is the bridge? Is it a small enclosed structure standing on heat-resistant risers on the deck? Is the deck in contact with the hull?

Well, then, unless the passenger is somehow floating above the chair like magic, that's precisely the route by which the LN2 ocean will leech the heat out of her/him: hull > deck > risers > bridge floor > rubber feet > wooden chair > cushion > space suit > clothing > skin > cryogenically frozen corpse.

Okay, let's put the human on an indoor swingset hanging from the ceiling by a very thin -- but extremely strong -- non-metallic wire. It's just one thin wire, right?

I think it won't make much difference. Unless you can insert a barrier across which no heat is transmitted, the human will freeze to death, and pretty quickly.

Any artificial heat source will also be drained. Even a blazing housefire will go out if you can just lower its temperature enough. Many kinds of electrical battery do not work when very cold. I think radioactivity might be unaffected, but we harness that energy by heating water to steam which then drives a turbine -- and I'd guess that the cooling effects of the LN2 would be more than enough to keep the water frozen solid unless you pulled all the control rods out of the reactor and let it go critical. That would probably melt the ice, just before vaporizing the reactor and the human and the boat.

And none of this addresses the likelihood that the structural integrity of some parts of the boat will fail when they get cold enough, which could lead to some kind of partial physical collapse, bringing the human in contact with the deck or hull and thus much closer to the LN2.

And none of this depends on the planet having an atmosphere. It's heat transfer through indirect physical contact with the LN2 via the hull and everything the hull supports.

• It's never impossible for a vessel to displace its own weight in fluid, you just need to make it big enough (although you do start to run into practical engineering problems of strength and rigidity). A boat designed for an LN sea just needs to have 25% more volume with the same weight. This is totally feasible, as the weight of the boat is mostly related to its surface area, which increases more slowly than the volume due to the square-cube law. Jan 29 at 16:07
• With good insulation, the heat loss is actually really slow. A good dewer full of LN2 doesn't feel significantly cold on the outside. Sure it will eventually equilibriate, given no source of heat in the boat, but it wouldn't be that hard to insulate it so well that the body heat of the passengers kept it warm. They need either 3x the insulation, or 3x the fuel of an Antarctic outpost. Feb 17 at 14:09

Absolutely. A very common procedure in biology is to wrap a bit of aluminum foil around the bottom of a vial or something, put in a bit of "embedding medium" such as O.C.T., take a bit of tissue, such as a lobe of mouse liver, and mash it into the middle of this gooey medium, and drop the resulting little boat into liquid nitrogen to freeze. Often it will float around on the surface. Once frozen, the foil will be removed and little slices of the rest will be cut with a microtome. (My condolences to your astronauts if they get caught up in that)

Moral: a well designed boat containing a lot of empty space can float - even if it is made out of steel, which is far more dense than water... or liquid nitrogen.

Humans are capable of insulating liquid nitrogen from absorbing heat from its surroundings. The usual approach to keep liquid nitrogen insulated from the atmosphere is a specialised type of vacuum flask called a cryogenic storage dewar. If the boat's hull and cabin are fully sealed and made from materials with excellent thermal insulation, it will not require too much heating energy to keep the interior of the cabin warm. Vacuum insulation on a large scale would be tricky. Aerogel would work but is very expensive. There are many commercial insulators (polyurethane foams) that are much better than aerogels. Some boat hulls have a rigid polyurethane foam core sandwiched between fiberglass skins.

• Vacuum insulation would be no problem for a bunch of folks who are traveling to other planets, with the added bonus that vacuum would be very buoyant. You'd need the extra buoyancy due to the lower density of liquid nitrogen. +1 Jan 29 at 13:59
• However: we're talking about a boat on a different planet. The manufacturing costs of aerogel won't be that much of a problem. (AND that stuff is light af, which is exactly what we want for stellar cruises) Jan 29 at 14:55

Several other answers have mentioned the threats posed by the cold to the boat's structure and its inhabitants. But if you have a good power supply, there might be an opportunity here to lessen that cooling effect and simultaneously increase your boat's performance.

If you place droplets of water in a frypan heated to around 180°C, they will boil away quickly. But if you heat that frypan to around 195°C, the droplets will last much longer, skittering around the surface of the pan.

The reason for this is the Leidenfrost effect. Above the Leidenfrost temperature, which for water is about 193°C, the water in contact with the pan boils, creating a cushion of steam in between the pan and the liquid water. Although steam is hot, it doesn't transmit heat as efficiently as direct contact, so the droplet heats up more slowly (despite the pan being hotter) and thus boils more slowly. Meanwhile, the droplet is essentially hovering, so it experiences almost zero friction, hence the skittering around the pan.

I don't have the physics knowledge to work through it in detail, but perhaps the same principle could be applied to create a kind of hovercraft that uses a Leidenfrost effect instead of a fan to generate a cushion of gaseous nitrogen, simultaneously insulating the boat against the cold of the lake and giving a near-frictionless ride. You'd then want something like a fan for propulsion.