Since the second edition was published in 2007 a number of important changes have and are taking place which relate to ship propulsion. Among these are the developments arising from the IMO's initiatives on the Energy Efficiency Design Index and the bringing to fruition of their earlier work on hull coatings stemming from their resolution on the subject in 2001. In addition to these legislative initiatives is a greater understanding of the physics associated with cavitation development and collapse and its subsequent erosive effects on propeller materials. Moreover, some new types of propulsor are being developed while in other technical fields there is a greater awareness, for example, of the effects of shipping activity on the behavior of marine mammals. It is the intention of this third edition to capture these and other developments that have occurred. In addition a certain amount of rearrangement of the subject matter has also taken place.