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Diesel-electric may be your best bet now

Joseph Garasic thinks the time is right for boat buyers to at least consider a diesel-electric propulsion system.

Fuel prices are up. Going green seems to be the right thing to do. Boaters always want more reliability, and they need more electricity for the all-electric boat — for stoves, ovens, refrigerators, watermakers, air conditioners, heads, televisions, stereos, water heaters, pumps, thrusters.

Garasic, 59, president of trawler and sportfish builder Legacy Yachts of Largo, Fla., thinks a diesel-electric propulsion system can address these issues in a more efficient and ultimately more economical way than a standard diesel or gasoline power plant.

“We certainly see a future in this,” Garasic says. “I just think it’s going to take a little while for any company to commit to diesel-electric-only on their boats.”

Garasic is offering the OSSA Powerlite diesel-electric system by Glacier Bay ( ) as an option on all 10 of his full- and semidisplacement trawlers and 18- to 37-foot sportfishing and dive boats. The first of his diesel-electric vessels, the Legacy 323, is a 32-foot single-engine, full-displacement, aft-pilothouse trawler that tops out at 8 to 9 mph.

Diesel-electric is relatively new to yachts, but it has been tried and proven on ships. Most passenger liners and some cargo-carrying ships have switched from conventional to diesel-electric propulsion, and the U.S. Navy powers much of its fleet with diesel-electric, Garasic says.

The major components of the Legacy 323’s diesel-electric system are a 13.5 kW variable-speed diesel generator, a 35-hp DC electric propulsion motor, and a power distribution box, or bus. The generator produces the electricity and sends it to the bus, which routes the power as necessary to the electrical accessories — air conditioning, water heater, stove, watermaker — as well as to the electric propulsion motor, which is coupled directly to the shaft. For offshore cruising, Garasic recommends a second, smaller generator as well, to serve as a redundant power source in case of a failure.

He hasn’t had a chance to sea-trial a diesel-electric Legacy yet, but he says it has the potential for big fuel savings. The reason: With a conventional diesel engine a skipper may have to operate at speeds well below its most efficient range in a harbor or waterway or push the engine well above its rpm “sweet spot,” for instance, when fleeing bad weather. And while cruising, the diesel often operates at the same speed going up a wave as it does surfing down it, which wastes fuel.

In a diesel-electric system, the propulsion source is decoupled from the prop and responds to the loads on the electric motor. With a variable-speed, or variable-frequency, generator and advanced electronic motor controls, the speed of the generator is matched to those loads instantaneously so that at any given time the generator runs at its most efficient speed for that load, says Garasic. Whether the boat is climbing a wave, surfing down it or revving up in the trough, the generator should always be adjusting its speed to changes in loads and close to its most efficient operating speed. This results in fuel savings and less strain on the generator.

“You can go all day long at top displacement speed without additional wear and tear,” he says. “You’re not pushing it at a high rpm.”

Garasic says efficiencies also are achieved with props designed for high-torque electric motors and by eliminating the transmission and resulting energy loss in the transfer of power between the motor and the prop. (An electric motor doesn’t need a transmission because its power output to the props is controlled entirely by electric impulses.)

Note this caveat: Use of diesel-electric power to propel a boat and supply its electricity may be desirable on a vessel like the Legacy 323, where it replaces a small-horsepower mechanical diesel. But today’s larger-horsepower, electronically governed diesels — especially HEUI (hydraulically activated, electronically controlled unit injection) and common-rail engines — are very efficient over a wide range of loads, including loads as low as 20 percent, and likely will prove for the foreseeable future the engine of choice for most recreational purposes, says Soundings contributing writer John Love.

But Garasic says efficiency is just one of diesel-electric’s advantages. He says a diesel-electric boat doesn’t depend on batteries for electric power, though the 323 does have four of them for ignition and for short-term power needs when the generator isn’t running. One power source meets virtually all of the boat’s electrical needs. The electric motor is ultra-reliable, going 40 years, according to some reports, without repair except for maybe bearing replacement, he says.

“They are indestructible,” says Garasic. “They don’t require any maintenance at all.”

The OSSA generator is encapsulated in insulation for quiet operation, and because electric motors have an enormous amount of torque, the 323’s 35-hp motor replaces a 56-hp Yanmar diesel, Garasic says. “And that’s way more than we need,” he says.

The generator can go virtually anywhere on the boat, and the small electric motor fits so low in the stern that it opens space there. With diesel-electric he can fit twin electric motors in his 32-footer now, if someone wants them, or maybe add a stateroom amidships. And since the power plant is smaller and operates more efficiently than conventional diesel, it produces fewer emissions, he says.

A 323 with conventional diesel power costs about $150,000, Garasic says. With diesel-electric, the cost is 5 to 10 percent more, but he stresses that Glacier Bay doesn’t just replace a diesel engine with a generator and electric motor; it provides a carefully designed system.

Spurred by the auto industry’s adoption of hybrid technology and intrigued by its successful use on ships, Garasic began investigating diesel-electric as an alternative and possibly more efficient power source for his boats. His inquiries led him to Glacier Bay, a 14-year-old Oakland, Calif., R&D company that has done contract work for the Defense Department and specializes in permanent-magnet motor technology, advanced motor controllers, and high-performance, variable-speed DC generators. The company builds electric motors from 20 hp to 800 hp and generators from 6 kW to 200 kW. Glacier Bay also has developed its own power distribution boxes and provides as part of its system high-efficiency accessories such as air conditioners, refrigeration, stoves, heaters, bow thrusters, windlasses and battery chargers. It also provides a monitoring system and digital console with readouts for all of the system’s components, as well as a joystick directional/speed controller. It is a total system.

Garasic says fuel savings are not a foregone conclusion with diesel-electric. The system’s components must fit together, and each must be designed for maximum efficiency and compatibility.

Garasic also offers an articulated rudder — a rudder with a trailing edge that functions independently of the main rudder and allows the helmsman — or autopilot — to make subtle adjustments. He says that, too, should deliver a reduction in fuel consumption.

All that said, Garasic is careful to point out that applying diesel-electric propulsion to yachts is in its infancy. There isn’t a lot of operating history to draw from in systems downsized for pleasure craft.

“We felt like we were out there on the edge when we committed to the system,” he says. But he says it looks like a strong alternative to conventional diesel. “If it’s going to be cleaner, quieter, save fuel, reduce maintenance and give you a total electric boat by putting a generator aboard, then the totality of the concept makes sense.”

For more information, contact Legacy Yachts at (727) 584-8100.