Blooper

An image of the upside-down Poseidon appears on a computer screen in the Navy's "mission room" long before they have discovered what's happened.

The hole that is blown in the ship could not have turned the whole ship over. It would only have sunk the way Titanic had done, only by the stern instead of the bow.

The captain's rank insignia is that of a first officer.....and he is the captain, not the acting captain.

The commandos blow a nice clean "hole" in a roll-up steel door and the commandos enter the building. In the next scene, only seconds later the entire door is missing.

There are actually two doors. The one they blow the hole in is the exterior door and the one that is missing is inside the building itself. Re-watched that scene and you can easily tell that it's two separate doors and two different rooms.

When Belle swims the under water floor she is taking the rope with her. The rope is visibly floating freely, however back at the other end, the guy is holding the rope under tension.

When the movie cuts to Sydney at the cruise liner headquarters, it's shown as daylight, possibly around 8 or 9am. Problem is, when Poseidon capsized it was only 10pm in the middle of the Indian Ocean. Sydney is only a few hours ahead of that area and thus it should be the middle of the night.

A woman is able to send a distress email even though the terrorists have cut all ship-to-shore communications, the ship is on emergency power, and the antennas and satellite dishes are underwater and pointed at the ocean floor.