system
Given the following post, respond as if you're commenting on Reddit:
human
ELi5: When giant ships like the Titanic sink is there a whirlpool effect that can drag people under when the ship fills with water? Can someone please explain why or why not this would happen?
gpt
Let's get this out of the way.  
The effect is a real thing that happens with large ships.  
The Mythbusters did one small scale test, with a boat far too small for the effect to be noticeable.   
There are many accounts and engineering studies showing that the effect happens.  
You need a large ship such as the battleship HMS Hood, and it needs to go down fast (the Hood went down in a few minutes after it blew up)  

As to why it works. 
Ever move you hand through a pool of water?
Behind you hand there’s less water because your hand pushed it away, so water fills in that place. The water moving into fill that place is what’s sucking you down.  
If your hand moves fast, the water has to move fast to fill the space.
  
Also there’s air trapped in a large ship that bubbles up to the surface as the ship goes down. In some cases, the bubbles make the water light enough to make it impossible to swim or float. The air going up also displaces water, causing it to rush in from the sides.