Supercargoes are people on a ship who are in charge of the cargo, which is all the things the ship is carrying.
Supercargoes are important because they make sure all the things on the ship are safe and in the right place.
Examples:
The supercargoes made sure all the boxes were stacked properly.
The supercargoes counted all the things on the ship.
When the ship arrived, the supercargoes checked that everything was there.
The supercargoes were like the bosses of all the things on the ship.
The supercargoes were like the kings of the ship's stuff.
The supercargoes were very busy making sure everything was okay.