sinking ship

does a sinking ship really cause suction like in the movies? if so, how come?

It sure does. Especially if it is going down fast. As the ship travels from the surface to the sea floor the surrounding water is constantly displacing that piece of the ocean once occupied by the ship. Where there was once no water, there now is. This requires motion. This motion translates as suction.(as water fills what would otherwise be a vacume.)

This would be a lot easier if I could post pictures.

Yes, a sinking ship does cause suction. Imagine the ship at any given instant. Now imagine it a second later when it has sunk one foot deeper. That foot of space was occupied by the ship a second ago but now there’s nothing there. This creates a partial vacuum which pulls the surrounding water in to fill the empty space.

Although suction certainly does exist, I’m guessing it gets overstated. In the movie version of Titanic, even Leonardio DeCaprio couldn’t stay afloat with his beer-belly alone, however, witnesses on lifeboats reported that infact there was very little suction because the Titanic sank slowly.

      • When a large ship goes down, there isn’t really suction, but you often can’t immediately stay afloat in the water. Depends on the type of ship, and oil rigs also do it too.
  • Normally fresh water weighs about 62 pounds per cubic foot, with sea water a bit heavier. The water in your body is also about this heavy. Swimming in water that is about the same density as that in your body is what we are all used to.
    When a ship sinks, all the compartments tend to leak air until they flood. Depending on the structure of the ship, this can take a few seconds or a few minutes. The air ecscapes into the water and breaks up into lots of tiny bubbles.
    These bubbles move upwards as normal, and to an extent push the water along with them. The problem is that the air is much lighter than the water that it displaces. If ten percent of the water is displaced by air, then it’s practically the same as if you were trying to swim in normal water with 10% of your weight extra to support. The more bubbles in the water, the harder it becomes to stay at the surface. At some point, you will sink no matter how hard you try to swim.
    If you go under water in such circumstances, I am told the best advice is to first detirmine which direction you are sinking, and then swim sideways. This supposes you will exit the region of bubbles sideways, and be able to float back up to the surface.
    You might think that the rising column of bubbles and water would push you up if you stayed in it, but you’d be wrong. The net effect is that because your body is relatively denser than the sea/air mix, you will sink faster than the bubbles will rise no matter how many bubbles there are.
    An in-law once worked on an oil rig and told me this, as we were watching the Titanic, no less. He also said that in water as cold as the North Atlantic, you’re *ucked if you go down in the foam, because the cold water makes it almost impossible to hold air inside your lungs. It is a physiological reaction/instinct to try to respirate when you hit the water, and there ain’t no air to inhale where you’d be. You probably wouldn’t come back up alive. - MC

I keep seeing the word “vacuum.” There is no vacuum involved, only air and water, twisted metal and soon-to-be-corpses.

“The boats were full of seamen.” - Titanic survivor

Nickrz and MC are right. I kayak and whitewater can have different densities depending on the ammount of air mixed in with the water.

I’ve read accounts of several shipwreck survivors who stated that when the ship went down they simply swam away. No suction at all.

I don’t have the book with me right now, but a co-worker had a first-hand account by one of the survivors of the Titanic, and in this particular case he reported strong suction at the time of sinking. He vividly wrote about being pulled underwater for a long period of time when the ship went down, and was barely able to make it to the surface. He also said that on the surface he found himself surrounded by a number of bodies of people who he believed had been pulled under with him, and who hadn’t been able to hold their breath long enough to survive. (He was one of the very lucky few who was later able to swim over to a collapsible lifeboat).

From what I’ve read, some ship sinkings have a strong suction, while other boats sink with barely a ripple.