Goofs

When Laura spots Peter through the telescope, Peter is looking off at an angle as if he is waving and smiling at a second ship that is present.

Nearly all the ship interiors are filmed with very little movement. What is happening in the interiors does not reflect what is happening in the ship exteriors. This is particularly noticeable towards the end of the movie where the ship is now terribly lop-sided.

The balloon would not be allowed to float untethered since there would be no way to steer the balloon back to the ship. It would be totally at the whim of prevailing winds. The fixed-location engine would be totally useless to steer the balloon since there would be no way to rotate it to the direction opposite of the direction they wished to travel.

When the ship encounters the tsunami, it is also beset with storm-level high winds, which would not occur with a tsunami in the calm weather at the time. With the nearby force of the volcanic explosions, however, there would certainly be very strong winds. The 2022 Hunga Tonga-Hunga Ha'apai eruption was particularly notable for generating winds exceeding hurricane force, reaching up to 450 mph.

The Western characters wrongly refer to the tsunami as a "tidal wave" (the Asian characters use the correct term). Those 2 types of sea wave have different names because they have different causes (the one in the movie is caused by the volcano not the tide). That Western error was almost universal at the time though across the media, and tsunami did not become the accepted Western name too until the Boxing Day Tsunami of 2004.

As close as Batavia Queen was to Krakatoa, at a bare minimum, every person on the ship should have been rendered completely deaf. In real life, Krakatoa's third eruption caused a spike of 2.5 inches of mercury in the barometers on the outsides of the boilers in the Batavia Gasworks, 100 miles away in what is now Jakarta. This enabled researchers to measure the decibel level of the explosion as 180 dB at 100 miles distant. This means that at Krakatoa, the explosion was approximately 310 dB. Sailors forty miles away in the Sunda Strait saw the sound wave traveling across the surface of the water and had time to put their hands over their ears, but were nevertheless completely deafened, many knocked off their feet, and several vomited from the concussive force of the noise.

Near the start of the film, some boys are looking at the volcano through wooden tubes. The camera is looking upwards to their faces, yet the view of the village behind them is one that is looking down from a height.

The birds at about 21 minutes into the film were shot with spherical lenses and not properly desqueezed for the film's 2.35:1 aspect ratio.

When the diving bell operator asks to be turned to port, the view moves to the right, which is starboard.

Krakatoa is, in fact, west of Java.

Near the start of the film, some boys are looking at the volcano through wooden tubes. As they do not have any lenses, all this would do would be to restrict the boys' field of view.