Learn French: Nous voyons les dockers décharger la cargaison du navire. - We see the dockers unload the cargo from the ship.

No, you still use the infinitive décharger! In English, we can say "I see them unload" or "I see them unloading," but in French, verbs of perception like voir, entendre, and sentir are followed by an object and an infinitive verb to describe the action.

Could I change the word order and put décharger before les dockers?

Yes, you can! When the object is a noun (like les dockers), French allows you to put the infinitive either before or after it. So, Nous voyons décharger les dockers is also completely correct, though the order used in this sentence closely matches English.

I learned that "boat" is bateau. What is the difference between bateau and navire?

Bateau is the general, everyday word for any kind of boat. Navire refers specifically to a large, sea-going vessel like a cargo ship or a naval ship. Since they are unloading a large cargo (la cargaison), navire is the most accurate word here.

I recognize charger in décharger. How does the prefix dé- work here?

It works just like "un-" or "dis-" in English! Adding the prefix dé- (or dés- before a vowel) to a verb reverses its action. Since charger means "to load", décharger means "to unload".