So in order to know what we're talking about (not the fashion these days, I know), I assume you're referring to the ship in the image attached below.
It's obviously not a real vessel but a CGI interpretation of what a troop ship might have looked in the 1880s, although I would say it is not unreasonable. I counted ca. 16 ventilators, which would befit the period where one would essentially rely on wind speed for the circulation (no proper electric fans to assist until the 1890s at least, and then only on state-of-the-art vessels. RMS Mauretania, although probably twice the size and a good 20 years later than what the film purports to depict, had 14 pairs of ventilators on the superstructure alone, if I am not mistaken. You'll need one or more ventilators to funnel in fresh air to belowdecks and a similar number to guide it out again, and again, it's the tropics.
Now, the film is obvious a fantasy piece with an atrocious mangling of history, but I think this depiction, while suffering from that bland CGI aesthetic with no real expert knowledge, is reasonably realistic in my book. The steamboat Adelaar being a real ship looked much better, obviously.
But your time would be better spent watching The Search for the Nile when it comes to Darkest Africa than this.

If it must be the Congo, the Tim Roth Heart of Darkness would be more faithful if despairing.