**Preface to "Selected Papers from the Sixth International Symposium on Marine Propulsors"**

Marine propulsors are key components of the many thousands of ships operating in oceans, lakes, and rivers around the world. The performance of propulsors is a vital component in assessing the efficiency, environmental impact (including impact on marine fauna), and safety of ships. Propulsor performance is also important for crew and passenger comfort. New types of propulsors with electric drives, flexible blades, and multi-stage propellers require new knowledge and improved tools. Innovative main or auxiliary propulsor types, using renewable energy from waves or winds, are also being commercialized. The improvement of computers and computational fluid dynamics creates new opportunities for advanced design and performance prediction, and new instrumentation and data collection techniques enable more advanced experimental techniques. This book is devoted to bringing the latest developments in research and technical developments regarding the hydrodynamic aspects of marine propulsors, to the benefit of both academics and industry. It consists of 19 peer-reviewed scientific papers previously published in the Journal of Marine Science and Engineering. Seventeen of these papers are improved and extended versions of papers presented at the Sixth Symposium on Marine Propulsors in May 2019 in Rome, Italy, while the remaining two are completely new submissions. The Symposia on Marine Propulsors are held bi-annually; the next one will take place in Wuxi, China in May 2021.

> **Kourosh Koushan, Sverre Steen** *Special Issue Editors*
