While in the ventilation shaft, Robert asks the group below for a ring or a coin, something so that Connor can get the screws loosened. Jennifer states she can't get her hand in her pocket, she already showed her father her ring, and put it on her finger earlier before crossing the grand lobby across the fire hose, her ring was on her finger, not in her pocket.
When Dylan, Conor and Maggie are running to get to the bow thruster room the water is following them very fast but when they reach the room the water isn't following them at all.
Watch the Captain just after he introduces Gloria. There is a shot of him stepping off the stairs at the side of the stage and walking towards the crowd, clapping. They show a closeup of Gloria, then a shot from the balcony. If you look at the side of the stage, the Captain is walking off it again.
At New Year's, Gloria is shown walking up, and clinking glasses with the chief officer on the stage. In the next shot from the balcony, they do it again.
During the capsizing sequence the ship, both inside and outside, continually shifts degrees that do not fit with the tilt in the next shot or another view from the same room.
Screw type propellers designed to work in water, are very poor at moving air, as they are not aerofoil type propellers like the ones used on airplanes. Therefore they would not be able to cause a huge pressure difference in a bow thruster pipe.
The ship was traveling the North Atlantic (London to New York) on New Years, meaning the water would be extremely cold. The main stars of the movie would have died from hypothermia, or at the very least they would have been freezing cold and barely able to function.
A single wave on its own would not be able to overturn a cruise ship 180 degrees. At most, a wave would knock the ship on its side 90 degrees. When the RMS Queen Mary, which inspired the original book, was nearly capsized by a wave it tilted about 50 degrees. Even if additional waves hit the ship overturning it 180 degrees it wouldn't stay that way. Large vessels like cruise ships and battleships are designed so they won't stay upside down even if they got to that point, naturally returning to 90 degrees. The USS Oklahoma only stayed upside down after getting the mast stuck in Pearl Harbor's mud, while the SS Andrea Doria settled at 90 degrees until it sank.
There couldn't have been any working electricity. After the ship capsized, the generators wouldn't have been able to maintain a fuel supply, not to mention generators were falling and the fuel was burning up and exploding. This also means the thrust propellers wouldn't have been able to be running.
It is doubtful the vacuum created by the thrust propellers would be powerful enough to hold the extremely dense compressed gas cylinder against the access door, considering its heavy weight and its aerodynamic shape. It would be like trying to suck up a ball bearing with a vacuum hose. Even if it were strong enough to do it, that would mean it would be far too powerful for Josh Lucas' character to be able to fight, and he would easily get sucked right in.
When they are in the ventilation shaft, Dylan mentions to Elena about her "little brother". He then asks her if he is older or younger, to which she replies younger. If Dylan refers to him as a little brother it should have been obvious that he was younger than her. Dylan is trying to keep Elena calm. It's possible that he's assumed that her brother is younger in his haste and then realizes he doesn't know for a fact, so he inquires to keep her occupied.
When they are in the ballast tank, waiting for the hatch to open, you can see the top of Connor's head go above the water level at least once, even thought the tank is supposed to be full.
During the capsizing, there is a shot of the an indoor pool with a wave proceeding from the raised end down it's length. While dramatic, this wave cannot occur, as all water rises at the bottom end of tilting vessels.
At the beginning of the capsizing, in the control room, one of the crew member is sitting on a chair. A frame later, the chair is down with the crew member with it.
After they escape the ballast tank, Connor comes up from the water. He is obviously coughing, but there is no sound.
In several scenes in the ballroom sequences while the band is playing, the audio is out of sync with the picture.
When they are crawling up the ducting and Conor unscrews the bolts holding down the grate, there are two or three shots where a hair on the camera lens is clearly visible in the lower left corner of the shot. This was observed in the HD version of the movie, but appeared large and clear enough to show up in SD as well.
When the characters are swimming from the last ballast tank to the stairwell, while they pass the ladder, at least one member of the crew is visible kicking their feet behind the ladder.
Towards the end of the movie, fishing wire can be seen holding the raft steady while everyone is getting on it.
Towards the end when everyone is walking towards the bow and they come onto the flooded corridor, the fluorescent lights are all working even under water. The fact is they shouldn't be working at all. The ballasts do not like getting the least bit wet and would be shorting out. The fact that they are working under water, and the ones that are getting constantly getting wet are not arching or sparking is incorrect. The chances of them all getting electrocuted is extremely high. Water and electricity do not match at all.
Why would both propellers (at the end of the movie) be sucking air in (or out) at the same time? Bow thrusters would create a vacuum in the chamber no matter which way they are turning, when to Starbord they create a vacuum to suck water and push it to the port side of the ship, and vice versa.
After climbing into a ballast tank, the passengers need to fill the tank in order to open the pressure relief valve that will spill them into the next tank. Aside from the fact that the tank would be impossible to fill (the pump suction is in the air and the tank vent is underwater), and the fact that the pressure relief valve would not open (there will not be enough pressure at the top of the tank), this valve should not exist. A pressure relief valve in a ballast tank allowing water to flow into the adjacent ballast tank would defeat the purpose of having separate ballast tanks. Tanks are kept separate to trim or heel the vessel as necessary, while preventing water from sloshing and de-stabilizing the ship. Having one tank spill over to the next via a pressure relief eliminates that control, effectively creating a "Titanic" scenario where the tanks keep spilling over, forcing the ship to take on an extreme trim and potentially "nose dive" or roll. In the event that a ballast tank is over-filled, the water would simply spill out the tank vent.
The experienced fire fighter grabs the door handle briefly with his hands to see if it was hot. It is taught in elementary schools to touch the hot door (or in this case the door handle) with the back of your hand. This prevents burns from limiting the use of your hand.
Robert Ramsey exhibits behaviour that indicates why he "used to be a fireman", as he knowingly stands right in front of a hot door while Dylan Johns opens it, and fails to check if the extinguisher he's going to use even works.