Maximising the amount of cargo

Having a ship full of cargo makes good sense because the more cargo the ship carries, the more money the ship owner will make. It is also better for the environment to make the most out of the fuel being used to operate the ship.
To keep a ship safe, there is a maximum load it can carry. To get more cargo on board the ship’s captain can keep just enough fuel, with a bit extra to get to the next port. They can make sure they do not have too many stores or fresh water on board. This would also make a ship heavier and would reduce the amount of cargo that can be carried.