Goofs

The boat's crane extends over the starboard side. In reality, if a heavy diving bell is lowered over the side of a modestly sized boat, the overturning force will cause the boat to list severely or even roll over. For this reason, real boats used for lowering diving bells are generally equipped with a crane that lowers the bell through a hatch in the center of the boat's hull, or over the stern in-line with the hull centerline; this prevents the boat from rolling as the bell is lowered.

When the characters are trapped undersea in the diving bell, they simply leave by climbing up to a hatch, supposedly at the top of the bell. Such an action underwater would immediately flood the bell. Yet, not even a drop of water enters the bell when they exit.

It's blatantly obvious that the diving bell prop hanging from the boat's crane is far smaller than the film set of the bell's interior; the prop is only about 6 feet in diameter and 8 feet tall, while the set is large enough for 4 adults to walk around without crowding.

Characters are seen climbing down the ladder into the diving bell interior before the dive, but the diving bell prop has no visible hatch on the top, nor any apparent provisions for the crew to climb aboard while it hangs from the ship's crane; in fact, the prop hangs from a hook that attaches where the top hatch should be.

When the first diver surfaces in the caverns, the camera pans up to show some rock formations. Above halfway up, you can clearly see some square-cut pieces of cardboard or other man-made material lodged between some rocks.

When the characters swim up from the diving bell"hatch" they are clearly just swimming up from *behind* the (quite small) diving bell, and not through any narrow hatch.

When Dale gets upset after reading a note from Tom, she throws her ring over the side of the boat. Even though they are far away from shore, the ring appears to land in water that's only around a foot or so deep. Not only does it look too shallow for a boat that size, but within minutes the diving bell is lowered into water deep enough for the bell to be down over 1700 feet.

At about 35:20, one of the male divers says, "I've been following the rock formations. I can't tell one from the other." Then less than 2 minutes later at about 37:10, the same guy says, "I've been following the rock formations.... I've seen a definite change."