Subarmines surfacing through ice - can they get stuck?

[Llama Llogophile]

This is a photo of the USS Annapolis after surfacing through ice. There was a scene depicting this in the movie K-19, as I recall. I've read a few links that talk about how subs can only surface through one meter of ice unless they're specially strengthened, in which case they can get through 3 meters.

But how do they get back down? I don't imagine the engines are any help since they propel the boat forward, not down (at least from a standstill - when traveling forward they have dive planes to help translate forward motion downward). So I'm guessing it's done with air tanks. Seems like it would necessitate a hell of a downward sucking force. So how is that done, and is there any danger of the sub getting stuck in the ice?

[Darth Sensitive]

It can just go straight down by filling the dive tanks with water instead of air, making the submarine negatively buoyant.

[Xema]

Originally Posted by Mach Tuck

Seems like it would necessitate a hell of a downward sucking force.

It's the same "sucking force" that makes a bowling ball sink when you toss it in a swimming pool - namely, gravity.

[robby]

What Darth Sensitive and Xema said. Submerging is easy. Surfacing is the hard part.

As the OP alluded to, when surfacing, you need to find a relatively thin spot. The submarine comes to a complete stop, and uses compressed air to go up at a controlled rate. Going up too fast and hitting the ice too hard risks breaking things.

I participated in an ICEX some years ago, and our sub conducted this operation a few dozen times.

[ZenBeam]

It'll take some time for the ice to refreeze to the point it prevents the sub from diving. They could also have maneuvers to help prevent the ice from refreezing.

[robby]

Originally Posted by ZenBeam

It'll take some time for the ice to refreeze to the point it prevents the sub from diving.

The submarine would have to be encased in ice before that became an issue. Before that happened, the submarine would have bigger problems, like having an adequate flow of seawater flow to cool the reactor.

Originally Posted by ZenBeam

They could also have maneuvers to help prevent the ice from refreezing.

Sure--like not shutting down the reactor.

For what it's worth, the seawater exposed to the arctic air following a sub breaking through the ice generally freezes very quickly (i.e. minutes).

[chacoguy]

Originally Posted by robby

As the OP alluded to, when surfacing, you need to find a relatively thin spot.

How do you find a thin spot?

[Joey P]

Originally Posted by chacoguy

How do you find a thin spot?

WAG: Sonar? They already have it on board, right? I would guess that it can detect density/thickness as well as the distance to something solid.

[Whack-a-Mole]

I am guessing the OP is asking if the ice freezes along the hull thus preventing it from submerging.

Thing is, to do that, the ship would have to be more than halfway out of the water. That is to say, the widest part of the hull would have to be above the ice so the ice could freeze under the "fattest part" of the hull and prevent it from descending.

This never happens. A sub on the surface is never is this configuration. It'd want to tip over as its center of gravity would be too high. Subs sit lower in the water such that the widest part of the hull is well below the waterline.

So, when ice is around them most of the ship is below the ice. There is nothing for the ice to wedge the sub in place. The sub just slips straight down.

Perhaps the ice has some "sticky" power (i.e. frozen to the hull) but I doubt that would suffice to hold the weight of the ship submerging. Even if it did the sub has gobs of hot water (that's what nuclear reactors make afterall). I am sure they could spray the sides and melt the ice enough to get away if they had to.

[Qwakkeddup]

They also have, or had air lines that pump air under the waterline, keeping it agitated and therefore keeping it from freezing.

[Whack-a-Mole]

Originally Posted by Qwakkeddup

They also have, or had air lines that pump air under the waterline, keeping it agitated and therefore keeping it from freezing.

I am guessing bubbles would help but they do not prevent freezing.

[kombatminipig]

Originally Posted by Whack-a-Mole

I am guessing bubbles would help but they do not prevent freezing.

Interesting, because that's the exact mechanism many private boats use to keep themselves unfrozen during winter. Seems to work quite dandily, from what I've seen. I'm guessing that the bubbles in the picture weren't frozen in an instant, but were trapped under an existing ice sheet, where they were then frozen in place. As the ice sheet thickened, more bubbles added underneath.

[Whack-a-Mole]

Originally Posted by kombatminipig

Interesting, because that's the exact mechanism many private boats use to keep themselves unfrozen during winter. Seems to work quite dandily, from what I've seen. I'm guessing that the bubbles in the picture weren't frozen in an instant, but were trapped under an existing ice sheet, where they were then frozen in place. As the ice sheet thickened, more bubbles added underneath.

Well, the article has the temp there as -30C (-22F) so it was really freaking cold.

I have seen frozen waves too so moving water is not immune from freezing.

Considering we are talking about places in the Arctic Circle I am guessing such temperatures are not unusual.

[Machine Elf]

Originally Posted by Whack-a-Mole

I am guessing bubbles would help but they do not prevent freezing.

Bubbles that agitate the water and force warmer water to convect in from below can and do prevent freezing. The situation in your link is a top layer of ice that has prevented bubbles of gas from reaching the atmosphere. Those stationary bubbles then get trapped as the stagnant water freezes around them, thickening the ice layer and entombing the bubbles.

[Alka Seltzer]

Originally Posted by Whack-a-Mole

Perhaps the ice has some "sticky" power (i.e. frozen to the hull) but I doubt that would suffice to hold the weight of the ship submerging.

I think a sub that froze up very badly could be in trouble. If it was iced up along it's entire circumfrance to a depth of 3 metres, that's a lot of surface area. Like you say, as the widest part of the sub is below the ice, it could still probably free itself. However, it might need to pump a conisderable amount of water into it's ballast tanks to do so, leading to a rapid descent once it broke free, which could be unsafe in shallow water.

Someone could probably do the math and come up with some rough figures for the force required to free the sub, and the rate of descent once it did so.

[Sailboat]

As far as I know, it's only nuclear subs that surface through ice. If they somehow get frozen in place, the handy nuclear power plant ought to be able to get them out. Couldn't they redirect steam or heated water to melt their way out?