S/V Barbara Ann

Hybrid Propulsion Design

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And this is the reason why sailboats make great hybrid vehicles.  The hybrid car can only use its motors to generate power while braking, but a sailboat can do it whenever it’s sailing and, even when motoring, whenever it’s sliding down a wave in a sea.  The sailboat can use part of the power of the wind on its sails to push the boat and part, captured with the prop being turned by the water passing over it, to generate electricity to charge its batteries.

In the original layout of the Barbara Ann, we had some severe space issues in placing a big enough generator.  The deal with hybrid, however, is that your top speed is dependent on the size of your propulsion motor.  How long you can maintain speed depends on your battery bank size and generator size.  Even though we have a 34kW generator, we can output up to 50kW for an hour or so if we use BOTH battery and generator power.   In our implementation I’ve compromised on motoring speed to 7.2 kts but we have extra power available for a difficult channel or strong currents. 

You actually get one more very important benefit of electric propulsion.  Electric motors provide near instantaneous torque. With an electric motor you can start and stop on a dime even with adverse conditions.

The Project

I started by contacting every manufacturer that claimed to have any kind of a diesel electric boat solution.  They included some big companies like Bosch, Siemens, Fischer Panda, and Vetus.  Some smaller companies like Solomon and Glacier Bay. They included some startups or web-page-only companies with little more than an idea.  Nobody was shipping a true hybrid solution in my boat size.

That’s not to say that there weren’t some solutions for smaller boats and some solutions for ships.   It became clear that there was a big gap in the market between about 20hp and 400hp.  On the low side there are plenty of brushless DC motors that will do the job and the power is low enough that a battery bank is reasonable size.   As the displacement of the boat goes up a couple things happen. The power requirements move everything into a more industrial area and the size of the battery bank becomes unwieldy. 

I started the project looking at the low-end regenerative solutions.  My boat was too large for Solomon’s systems; the most widely installed electric sailboat solution. From there I started looking at the Fisher Panda and Siemens, both with higher power solutions.   Siemens could sell you a nice diesel electric solution that would power your aircraft carrier.  None of the higher end companies had a regenerative solution, just straight diesel electric propulsion.  These companies typically use a brushless AC motor and operate at 400 to 600 volts.

Most of these lower end solutions use a DC generator and brushless, permanent magnet DC motor.   They typically require 144 volts of DC power, and a battery bank of twelve 12-volt batteries. 

I worked for a bit with a couple of the middle tier companies but for the most part these companies have little more that a web site and a dream. 

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Bill & Barbara Southworth
39 Pickering Street • Portsmouth NH 03801 USA
Cell: (617) 905-6800 or (617) 905-6803 Fax:(888) 300-8888