Serial hybrid propulsion systems for displacement vessels, both recreational and commercial.

If you have been following the evolution of electric cars like Tesla, Nissan Leaf, and Chevy's Volt and Bolt, then you are already aware of many of the benefits of an electric drive train.

  • Electric motors are almost silent. The only noise you hear in an electric car are the tires on the road, and in a boat, the water rushing past the hull. Running a displacement power boat on electric drive is as close as you can come from the sensual experience of sailing.
  • Motors are reliable. The typical marine diesel has a life of 10,000 hrs before requiring overall. Some have more hrs in them, many have less. The motors we use have two moving parts and a service life between overhauls of 100,000 hrs. And at that point, all you have to do is replace two bearings.
  • Motors are powerful. Our motors can put out 335hp and yet be lifted by a man. Its foot print is a fraction of an engine of the same output.
  • Motors have full torque at 0 rpm. This means you can swing a large prop with higher pitch without fear of “lugging” or stalling, translating directly into increased efficiency, acceleration and even stopping power.
  • Motors are inherently more efficient. Much of the power produced by a diesel engine is wasted in heat. Modern AC motors can be up to 98% efficient. This is why the typical electric automobile can go 100 miles on a gallon of gas.
  • Motors are powered by electricity. This is obvious, but think about it. Regardless of the fuel (gas, diesel, natural gas, hydropower, wind, solar), they can all produce electricity. Electric drive means you are future proofed. Any source of electricity can run your boat, even when oil becomes prohibitive.

Serial Electric Hybrid Drive

Our default solution for displacement boats is a serial electric drive, with motor, batteries and propeller designed to work optimally with your particular boat. But how does a serial hybrid work? What are its main parts?

  1. The propeller is directly driven (straight shaft or sail drive) by an electric motor.
  2. The motor is powered by a bank of propulsion batteries. Except for small boats, the batteries operate at 400volts DC, just like cars.
  3. A typical battery range at cruise speed is 25-45 miles depending upon battery size. At half cruise speed, the range can quadruple.
  4. When operating within that 4-5hr cruise window, an electric boat can be charged at dockside.
  5. A Tier III clean burning diesel engine is mated with a powerful DC charger, dedicated to charging the batteries in pulse mode. As the boat is running and the batteries reach 20% charge, the generator automatically turns on, warms up and then charges the batteries (while the boat is still running at cruise speed) at anywhere from 1/2 to 1 1/2 hrs, depending battery/generator sizing.
  6. In an emergency, if the propulsion battery is compromised, the diesel engine is capable of providing electrical power directly to the motor (diesel electric mode.)

Why would I consider an electric drive?

  1. For the quiet. Next to sailing, this is the quietest most serene boating experience you can have.
  2. For the fuel savings. For shorter day trips, charging at dock, fuel costs are negligible. For a long trip (i.e. the Inside Passage to Alaska) you will save up to 50% over a current non-tiered engine, and 15-20% over the cleanest burning diesels. In a coming article we will be going through all of the factors that result in these kinds of fuel savings.
  3. For maneuverability. An electric motor coupled with a larger propeller is exquisitely controllable, making docking and slow speed maneuvers that much easier. This is why many of the canal boats in Europe, having to negotiate tens of locks per day have electric drive.
  4. For the power. If you have an older trawler, for example, re-powering with an electric motor will likely give you more sustainable power and speed for outrunning currents.
  5. For extended low speed motoring. Certain types of commercial craft must run all day long at inefficient slow speeds (e.g. research vessels dragging an array, a troller fish boat.) With electric drive, there is no inefficient speed. You can drift at 2 knots or run at maxim power as long as you like without fear of harming the “engine."
  6. To be green. Power boating is a carbon intensive enterprise, not just when cruising, but when idling or trolling or docking. Hybrid drive will not only save fuel, it will run cleaner at all speeds
The concept of serial electric drive is simple enough, but the devil is in the details. Coming in future articles we’ll explore both the controversies and benefits of such a drive arrangement.