When Gus looks at the photo of him, Stu, and Tommy their poses are not of those when the picture was taken. For one, Stu is shown smiling while holding up his fingers to make the peace sign when in reality he was standing close to Gus and slightly grinning.
The ghost ship is referred to in dialog and in captions as "H.M.S. Queen of Scots", however, the HMS designation stands for "Her (or His) Majesty's Ship" and is a designation only for Naval vessels. A cruise ship may be RMS (Royal Mail Ship) or some such, but not HMS.
When Stu locks Tommy and Charlie in a small compartment and opens a valve to flood it, they hook a two-fold block and tackle to the latch wheel on the hatch, but the hook immediately slips to the hub of the wheel, practically negating any leverage they may have had... also, as Charlie heaves on the tackle, she is floating, and would have almost no weight to apply to open the hatch.
Before Stu attacks Morgan in the engine room, when Morgan is cocking his gun, you can look inside the barrel and see that it is a fake gun (the barrel is blocked).
A caption at the beginning states 'Sargasso Sea, South Atlanic Ocean'. It's actually in the North Atlantic.