Just before Ishmael and Queequeg meet Elijah, they walk past a moored ship which has a Plimsoll mark painted on her hull. The scene takes place in 1841, but Plimsoll marks were not devised until the 1870's.
In the scenes with the Quaker characters, despite Herman Melville's correct use of "thee" and "thou," the two Captains frequently misuse "thee" as the subject, when it is only ever used as the object. For instance, the Peleg and Bildad will frequently say phrases such as "hast thee" or "art thee" when the correct use of this mode of speech calls for "hast thou" or "art thou."
Early at sea (on the Cape Verde grounds) the first whale is spotted and then harpooned by harpooners on each of the three boats. As the whale runs, towing each boat behind him, a call of "man overboard" is made and we see a close-up of a crewman cutting his boat's harpoon line and then another shot of both remaining boats being towed by the whale, but in the next shot, facing forward from the whaleboat's perspective, we see three taut lines leading back from the whale.
When the white whale rams the ship, the main mast breaks and comes down, crow's-nest and all, hitting the cabin boy. The whale circles the ship creating a whirlpool; when we see wider shots of the ship spinning and sinking, the mast is back up.
During the final battle between the whalers and Moby Dick, the weather goes from grey and foggy to brightly lit blue skies to patchy clouds and back again depending on the camera angle. It is obvious that it was stitched together from multiple takes under drastically different weather conditions.
The Pequod enters the waters near Bikini at new moon, where Ahab believes the white whale will be. The next night scene shows a full moon, yet the crewmen state that "the moon's lost his horns" and, referring to Ahab, "7 days and 7 nights on watch". Both statements indicate that the moon should be at about First Quarter, not full.
The way the ship was moved away from the pier was incorrect. The crew is shown hauling a line from the pier. This would not make the ship move forward.
To move a ship out of the harbor, it is therefore, necessary to provide something to pull against. A special anchor, called a kedging anchor, is carried as far from the ship as possible by the longboat and then dropped to the seabed. The remaining crew pull the ship out to it winding the line around the capstan or winch, and then it is hauled up and the process repeated as many times as necessary.
During the scene when the masts and Ahab's harpoon are covered with St. Elmo's fire, the luminous phenomenon was shown as a green glow. Physically, St. Elmo's fire is a bright blue or violet glow, appearing like fire in some circumstances, from tall, sharply pointed structures, so the color of the phenomenon is incorrect.
When Captain Ahab repeatedly plunges his harpoon into Moby Dick, and pivots it back and forth freely at the surface of the whale's back, it is clear that there is nothing but empty space beneath the surface of the prop "whale", rather than the blubber, muscle and bone that would prevent the harpoon from pivoting freely.
Moby Dick's size changes from scene to scene. In the early scenes it looks almost bigger than the ship. In later scenes, however, it varies. After it sinks the Pequod, there's a moment when most the whale is visible above water level, and it's only about 10 times the size of Ahab's body, clearly seen tangled atop.