Direct drive or diesel-electric? This question arises during the initial development stage of more and more vessels and is presently being debated with both smaller and larger vessels. Issues that must be addressed when evaluating the propulsion options include the initial & lifecycle costs, system reliability & performance, maintenance & manpower requirements, as well as vessel arrangement options.

Diesel-electric propulsion presents some formidable advantages over direct drive for many vessels with minimal or no cost increase and the potential for significant savings in maintenance and fuel over the life of the vessel. The system reliability, arrangement flexibility, and energy transfer aspects are unmatched. It is especially cost effective with large auxiliary equipment operated when main propulsion is minimal, including thrusters and cargo handling equipment. Direct drive systems, however, have one major advantage over electric propulsion; they are simple and well understood by most operating personnel. Although extremely reliable, an electric propulsion system will require better training for the crew.

Regardless of the propulsion arrangement, the configuration of any electric plant supporting the propulsion system can vary tremendously and must be integrated with the operational criteria of the vessel to provide the most cost effective system. This is the primary motivation for this article; to provide owners, operators, and design firms with cost-effective alternatives for vessel propulsion, which can result in improved performance and reliability.