The main reason there are no people on the boats is that there are no heads on the boats and we don’t want to deal with the mess that they would make.
Actually, Ship Simulator is about ships and ship handling. People would add nothing to the primary goal of the sim, and would have an adverse affect on performance.
People enter missions only as passengers to be picked up and dropped off. Most ships have a limited number of places where people can be placed when the mission is created. Some vessels have static people aboard. None are animated, for the reasons stated above.
Marty
