Electric Marine Propulsion Motor: Core Knowledge for Modern Electric and Hybrid Vessels

An increasing number of shipping companies are implementing electric propulsion systems into their vessels, which has led to a vast increase in demand for electric marine propulsion systems. Electric propulsion systems are defined as electric motors that convert electrical energy supplied to them into mechanical power to rotate propellers and/or waterjets. An understanding of the electric marine propulsion motor is important not just to shipbuilders but also to system integrators and vessel operators in order to take advantage of this rapidly growing technology that provides significant fuel savings when compared to traditional diesel propulsion systems. The primary purpose of an electric marine propulsion motor is to provide propulsion power to vessels (i.e., boats, ships, offshore platforms, etc.) as compared to auxiliary power to equipment aboard vessels. Unlike auxiliary motors and auxiliary power sources that provide power to equipment aboard the vessel, propulsive electric marine propulsion motors provide the only means of movement of the vessel (propulsion) and also provide the necessary means of turning the vessel when not in motion (maneuverability).

Electric marine propulsion motors are generally used with either electric or hybrid systems, receiving electrical power through batteries, generators or energy storage media. The operation of an electric marine propulsion motor represents a direct impact on the efficiency of a vessel; the sound produced as a vessel operates is directly associated with the operation of an electric marine propulsion motor; the overall operational reliability of a vessel is directly influenced by the performance of the electric marine propulsion motor. Applications involving marine propulsion require motors designed to produce high torque (force/velocity) at low RPMs (revolutions per minute). Electric marine propulsion motors can provide the maximum amount of torque to propel a vessel at the instant an electric marine propulsion motor is energized. Electric marine propulsion motors can provide controlled voltage output and will thus deliver constant torque to propel the vessel. 

Electric marine propulsion motors are capable of producing high torque at low RPMs and thus are this same power will be available to propel the vessel for extended periods of time. Electric marine propulsion motors must perform stably through variable torque output, which occurs whenever the load on the electric marine propulsion motor is constantly changing based on the performance characteristics of the electric marine propulsion motor, as an example water resistance, speed and weight of the vessel (marine propulsion motors have constantly varying loads). 

Adapting to Harsh Marine Environments Marine environments provide unique challenges to the electric propulsion motor due to corrosion from the salt water and from moisture from humidity, vibration from the engine room, and changes in temperature (from hot to cold) thus providing many challenges. Therefore, in order to provide long-term performance from electric propulsion motors in marine environments, the manufacturer's design considerations will include the effects of the marine environment, such as using non-corrosive materials for motor construction, using reinforced insulation on electric marine propulsion motors, and providing sealed housing/enclosure structures for electric marine propulsion motors. Additionally, another critical design consideration when designing electric marine propulsion motor is that electric marine propulsion motors require effective cooling management because electric marine propulsion motors dissipate heat during normal operation whether they are in the enclosed engine room or submerged underwater.

Environmental Advantage of Electric Marine Propulsion Motors

The benefit to both energy efficiency and the environment created by electric marine propulsion motors is that they are much more efficient at converting energy into working energy than traditional marine propulsion systems. This factor significantly reduces the total amount of electrical power consumed by the electric marine propulsion motor when used on an electric or hybrid vessel, therefore increasing the overall distance the electric or hybrid vessel will be able to travel before running out of electrical power.

Electric marine propulsion systems are also environmentally friendly because the noise and vibration produced from an electric propulsion system is considerably less than that of a traditional mechanical propulsion system, therefore creating a considerable reduction in the level of underwater noise which in turn creates an increase in passenger comfort and enhances the protection of the marine ecosystem.

Compatibility with Today's Propulsion Technologies

Control of an electric marine propulsion motor may be achieved with very high precision due to its compatibility with today's control systems (i.e., both electrical and mechanical). Thus, the electric marine propulsion motor may be used to deliver power to the propulsion system of an electric or hybrid vessel, allowing for features such as dynamic positioning, automated docking, and regenerative energy management.

With the current evolution of vessel automation and vessel digitalization, electric marine propulsion motors are a key component of an intelligent, interconnected marine system.

Examples of vessel categories utilizing electric marine propulsion motors include:

•Electric or hybrid ferry;

•Leisure/pleasure vessel and yacht;

•Workboat/work service vessel;

•Inland waterway transport vessel;

•The autonomous and remotely operated marine platform.

The use of electric marine propulsion motors due to their versatility on both commercial and recreational marine vessels will be important in developing new boat designs as stricter emissions/mechanical requirements are implemented and the need for environmentally friendly marine transportation continues to increase.

The future of electric motors for marine propulsion will include the development of new electrical systems that utilize both new technologies in electric motor operation and new electric motor construction materials, and new means of controlling electric motors will enhance both the efficiency and the reliability of electric marine propulsion motors.

As the marine industry continues to evolve towards cleaner/more intelligent propulsion technologies, electric motors for marine propulsion will be a major contributor to the overall success of the marine industry's complete transformation, and not just the individual value of electric propulsion motors on a vessel level.