Unmanned and autonomous ships are a hot topic and many researchers are working on different aspects. However, in many cases, the research focusses on one aspect that is required for autonomous sailing, for example, navigation, communication or propulsion. In my research, I work on the assumption that a ship is crewed by 10 – 20 people, and that they all have a job to do. This means that to sail without a crew, all their tasks need to be replaced in some way. I use an algorithm to determine the effect of these replacement actions on the size of the crew. That way, I can identify several logical intermediate steps between a fully manned ship and a fully unmanned ship.