In the design of a marine propulsion system there are a number of interactions to consider. They result in both losses and gains and to achieve optimal efficiency these must be balanced in the best possible way. This is often not the case today, but optimization is performed on each component separately. The reason for this is partly the market, but also stems from a lack in understanding some of the effects, primarily related to that evaluation today is based on model scale data and not at real operating conditions. It is estimated that there is a large potential of reduced fuel burn, around 10% or more, if a better and more complete system analysis could be performed. The objective of this project is to map what affects the propulsion system and improve the understanding of these components, and to demonstrate how this can be used to achieve energy savings for newbuilds as well as for upgrading of ships of about 8 – 15 %.