Towards the start of the movie when the bottle is broken on the ships bow (Front), the ship rolls out into the water, it shows the propellers. The outer propellers have 3 blades not 4.
I think you will find that the ship in the opening video sequence was not the Queen Mary(She has only 3 stacks) the ship was actually the Olympic, Titanic's sister ship. The names on the stern of the tug boats are also blurred out because they probably say New York under their name.
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