How Does E-Propulsion Work?
Published: Monday, March 30, 2020
By: Jordan Tilton
We’ve all become familiar with the Toyota Prius and seen increasing numbers of Teslas zipping around the roadways. We’ve been hearing about “green” technology as a solution to make the environment cleaner and better, and, while these cars are celebrated for being revolutionary, this technology is also being built and integrated into the marine market.
In piggybacking on the last issue about how boating is evolving, this evolution of green technology is happening currently in the commercial marine market, and quickly approaching the recreational boating market.
There are multiple companies in both the commercial and recreational marine markets that are developing hybrid and fully-electric propulsion systems to eliminate having large diesel engines onboard to drive propellers through a traditional gearbox.
Hybrid Systems
A parallel hybrid system is slightly more complex than a fully-electric one in that it has more connecting pieces. First, there is a combination of designated variable-speed generators (diesel generators) for each propeller. Traction motors, similar to a traditional gearbox, turn the driveshaft and propeller, and battery banks power the propellers. These battery banks—otherwise known as Energy Storage Systems (ESS)—usually sit in parallel rows or stacks.
As the Captain is operating the boat on pure battery power for a time, he or she will monitor battery power from the helm. Once the batteries reach a minimum power threshold for safe operation, the power system onboard will automatically detect low battery power charge and will start the generators to rapidly charge the battery banks back to a safe level. Once recharged, the generators will automatically shut down and the boat is back to operating on pure electric power.
This function is all performed without the Captain having to start or stop or otherwise disengage any equipment. It’s a fully integrated and seamless system.
As these systems become more common, boat designers and manufacturers increasingly design the boat in a way that will allow it to utilize the variable speed generators in combination with the power from the batteries for maneuvering, turning, and faster speeds, if needed.
The designers and builders of hybrid systems work with individual operators and designers to determine a proper combination of generators and battery power in order to ensure safe operation for navigation and otherwise meets all approval from the USCG.
For example, a normal flybridge cruising boat might be equipped with a pair of Cummins QSM11 diesel engines, rated at 715HP a piece, resulting in 1,430 combined HP. A comparative hybrid system providing the same amount of propulsion would use a pair of Cummins QSL9 diesel generators, rated at 320HP a piece. The power provided is the same, but the horsepower required to do so is reduced by 790HP. This means a large fuel savings since the generators are only operating for short periods of time while charging the battery bank (ESS).
Fully Electric Systems
A fully electric system is just that. 
There is an ESS combined with an electric motor(s) to turn the propeller(s), eliminating the need for the variable-speed diesel generators as in the hybrid system. Once the batteries reach the minimum threshold of charge, then it is necessary to plug into a shore power charging system to get the batteries back to a safe operating range.
Because of the need to repower at shore, this system is most commonly used in short ferry routes. You can find it in operation in Europe and similar ferries are being proposed here in the United States. Some of these vessels will opt to have an onboard generator, strictly for emergency charging, but some do not; it all depends on the application.
While the recreational marine market may not be as quick to develop technology as the automotive or aerospace industry, I can assure you that there are companies actively investing millions of dollars and hours into making our waterways more green and less dependent on fossil fuels.
About the Author
Jordan Tilton has 14 years in the marine industry and is Director of Hybrid Propulsion Systems for a US-based manufacturer of propulsion systems for both the commercial and recreational marine industry. He also owns and operates JTA Yacht Delivery & Consulting and specializes in Great Lakes to East Coast yacht deliveries and currently holds a USCG 200T Near Coastal Master’s License
This article first appeared in the Spring Issue (Mar/Apr) 2020 of Great Lakes Scuttlebutt magazine.
tags: Boating 101, Engines, Environmental Impact, Generators
