Why do the doors of navy ships have those things?

Question

On a ship (Carriers, Battleships) why do doorways have a metal thing that yo uhave to walk over? instead of just walking past it, you have to walk over it, i think they're called knee knockers or something.

Answer 1

I'm just guessing here, not having been in the Navy... but I suspect it's so the doors can be watertight when closed, so flooding one section won't sink the whole ship.  

Answer 2

It helps with water tight integrity. If it was a regular door, it wouldn't seal properly.  

Answer 3

It gives a better seal when the door is closed and locked. If the ship were taking on water you could seal off the compartment so adjacent ones don't flood too, hopefully keeping the ship from sinking. If you look at the hatch (door) it has handles on it to make sure it latches tightly when it is closed. I also think rounded hatches are stronger.  

Answer 4

It's to keep them water-tight. And control the flooding of water from one deck to another.

Answer 5

To keep the door more water tight.

And with a little height then the water wont just sit there waiting for someone to open the door. So when the door is opened water wont come rushing in.

Answer 6

Keep water from going into a room as quickly