A drive to diesel electric?

Diesel-electric propulsion has been around for a long time in the commercial marine world. But voyaging sailboats have always relied on an auxiliary engine driving a prop shaft for non-sail propulsion. Now a well known genset company is working on diesel-electric propulsion for sailboats. Fischer Panda Generators, the American arm of the German manufacturer of marine generators, is adding one of their Whisperprop diesel-electric propulsion systems to a Catalina Morgan 440 sailboat.

The boat, dubbed Electra by Fischer Panda, is scheduled to be finished in November and will appear at boat shows like the Miami International Boat Show in February 2006. For two years now, Fischer Panda in Germany has had a similar system installed in a Bavaria 49, demonstrating the technology in Europe. “We’re the only ones producing diesel-electric power for the sailboat industry for boats 36 feet and up,” said Chad Godwin, national sales manager for Fischer Panda U.S. “We also think this will be attractive to the trawler market.”

According to Fischer Panda, the benefits of its diesel-electric setup include better fuel efficiency, greater range, less emissions into the environment, lower weight and quiet operation. This is an impressive and attractive list – will voyagers be convinced to make the switch to diesel-electric systems?

In terms of making engine changes, the biggest switch for most voyaging sailors was in the ’70s and ’80s when many boats swapped over from a gasoline-fired Atomic Four engine to a diesel engine. Since then, diesels have been the standard propulsion engine on sailboats and power voyaging craft, and diesel technology has seen a number of advancements: lighter engines, higher operating rpm, electronic controls and common rail fuel delivery, to name a few.

While diesels directly driving a prop via a marine transmission were taking over the world of recreational boats, diesel-electric systems were engaging in a similar conquest of the cruise ship market. Virtually every cruise ship built in the last 10 years uses diesel-electric propulsion. The largest of the liners, the 1,132-foot Queen Mary 2, launched in 2003, has a diesel-electric power plant that produces 118,000 kw and can drive the ship to a top speed of roughly 30 knots.

Obviously, the diesel-electric power plant for a 40-foot voyaging sailboat doesn’t need the power required to move the prodigious bulk of a cruise ship (all that buffet shrimp adds up). A voyaging-boat-size system is a bit more manageable. The Whisperprop system on Electra will use a Fischer Panda AGT-DE AC generator that has a nominal voltage of 400 volts, at a frequency of 400 Hz at 3,000 rpm. For propulsion needs, this high-power AC is then run through a motor controller that handles speed control and shaft rotation direction (for going astern).

The electric motor used on Electra will be a permanent magnet type turning a shaft and prop in a fairly traditional angled mount. And even though Fischer Panda and Catalina won’t be using it on Electra, one of the advantages of diesel-electric propulsion is the capability to place the driving motor and prop virtually anywhere in the boat and to mount the drive shaft/propeller horizontal (parallel to the waterline).

Due to the need to couple the prop shaft to the driving engine, a direct drive diesel system often has to angle the prop shaft as it exits the boat. An electric motor-drive, however, is much more compact and works well with a sail-drive-type unit (see diagram). Another advantage to an electric motor drive is seen on the cruise liners using this system; many of these ships are equipped with “azipods,” an electric motor in a azimuthing (rotatable) pod. The same idea of an electric drive that rotates around its vertical axis coupled with a bow thruster allows for greatly improved maneuverability for voyaging sailboats. Their angled single-screws have not always been great performers in this area. A sailboat equipped with such a setup would be far easier to direct in crowded harbors.

Other elements of the system are battery chargers for taking output from the AGT generator and charging the house battery bank. A final piece is an inverter for supplying AC power to the boat.

The major benefits cited by Fischer Panda: greater fuel efficiency, longer range and quiet operation revolve around the difference in using a diesel to drive the prop directly rather than using it to make electricity. Rather than operating the diesel at a range of rpm, the key to the diesel-electric approach is to run the engine at a constant speed, a speed that is optimized for efficiency. The result is better fuel efficiency, longer range and less emissions.

Another benefit springs from Fischer Panda’s experience with generator enclosures. The company has long offered gensets in sound-deadening enclosures that greatly reduce genset engine noise. The Whisperprop system uses such an enclosed genset. This, allied with the quiet operation of an electric motor makes diesel-electric propulsion a low-noise option. “It pretty much makes the unit inaudible when running,” Godwin said. Fischer Panda also claims that its diesel-electric system reduces the overall weight of the propulsion/electric generation package by 400 lbs.

“Catalina is working with us on this one,” Godwin said. But Fischer Panda plans to provide the Whisperprop packages to all boat manufacturers. “We’ll offer the Whisperdrive package to all boatbuilders.”

One of the drawbacks to this new product is one that bedevils many new approaches: cost. The Whisperdrive diesel-electric package (generator, motor controller, battery chargers, inverters) sells for $40,000. This is a substantial price for replacing the tried and true approach of the direct drive diesel. Will boat owners pay extra for diesel-electric propulsion?

By Ocean Navigator