With all the hype about diesel-electric drive systems, both automotive and marine, you'd think it was new technology. But you'd be (mostly) wrong. Diesel-electric propulsion has been around since before World War I. But the current application has new aspects that make it more relevant to recreational boaters"”particularly with the current push to maximize efficiency and minimize pollution.

Diesel-electric propulsion is pretty simple: a diesel engine drives a generator, which in turn drives an electric motor. That motor then drives the wheels of a car or, more importantly to us, a propeller. In marine installations, the engine and generator are optimized to run at the most efficient speeds with the best fuel economy. Though there are several variations, those are the basics.

But again, much of it is not new. In fact, diesel electric propulsion was first pioneered in submarines, which were powered by sources ranging from steam to gasoline engines. What is new is that we are starting to see widespread application of these technologies on vessels that can be purchased by the average boater – and boaters are interested.

In a Mad Mariner Technology Survey of 400 boaters this month, 70 percent said they would consider buying a diesel-electric boat and more than 50 percent said they look to this technology to make the greatest improvement to boating in the next decade.

PAUL ESTERLEThis type of diesel-electric drive was used in U. S. Navy submarines until the late 1920s and by the rest of the world until the late 1940s.The systems themselves are also getting highly evolved. What makes today's diesel-electrics different from, and superior to, those of old are their ancillary devices and systems. For example, solid state controllers now provide more accurate management of generators and motors, while consuming less power in the process.

PAUL ESTERLEStarting in 1928-29, the U. S. Navy switched to this type of diesel-electric propulsion system for their submarines.The addition of battery banks provides the opportunity to operate in a hybrid mode, either totally under battery power, under battery and diesel power or under diesel power while the batteries are being charged (and the addition of smart chargers has greatly extend battery life). Wind generators and solar panels can provide additional power for propulsion or battery charging.

On the surface, it would seem that adding all this gear to a system used to drive a boat would be less efficient, not more. However, the typical direct drive diesel propulsion system can only be optimized for a narrow range of performance. Operate out of that narrow band – either faster or slower – and efficiency drops off, increasing fuel consumption.

In a diesel-electric system, the power output of the diesel is matched to the power required, thereby operating efficiently and consuming less fuel. Carefully integrated systems can achieve anywhere from a 10 percent to 50 percent fuel savings over conventional drive systems.

COMMERCIAL ROOTS

The diesel-electric systems seen in recreational boats today have their roots in the commercial sector.

Diesel engines have been refined for decades, replacing steam turbines in ship propulsion, but those engines were still huge. The current record holder is the Wartsila-Sulzer RTA96-C turbocharged two-stroke diesel engine. These engines are available from six through 14 cylinders. The cylinder bore is just under 38-inches and the stroke is just over 98-inches. The engine weighs 2,300 tons, is 89-feet long and 44-feet high, producing 108,920 hp at 102 rpm.

These massive engines propel ships at impressive efficiencies but leave much to be desired in terms of maneuverability. To add maneuverability, pod drives were developed. The diesel engines drove generators; the generators drove electric motors housed in pods under the ship; the pods had propellers on the end and could be rotated to provide thrust in any direction. Multiple pods could be mounted anywhere underneath the ship, and the resulting maneuverability provided precise docking control as well as the ability to maintain a fixed location when coupled with modern GPS units (a useful feature on mobile drill ships and other oceanographic exploration vessels).

These units first appeared in tug boats where high maneuverability was a necessary requirement. Their use has since spread to container ships, RO-RO's (Roll On, Roll Off cargo ships) and even the new Cunard Queen Elizabeth 3.

The development of smaller and lighter diesel-electric propulsion systems for recreational craft has traditionally lagged behind the units designed for larger vessels. But that is now changing.

WWW.SHIP-TECHNOLOGY.COMAzipod drives turn the propeller by means of an electric motor housed in the pod itself. The pods can turn 360 degrees. Electrical power is supplied by a diesel powered generator.THE RECREATIONAL MARKET

Modern diesel engines, both normally aspirated and turbocharged, are light enough for use in diesel-electric propulsion systems for recreational craft. Steyr Motors, Glacier Bay and Fischer-Panda, among others, have started producing units that can be installed in recreational craft of almost any size.

There are several potential benefits in recreational craft. A diesel-electric propulsion system allows the diesel to operate at power levels appropriate to the power required, saving fuel. This efficiency also translates into fewer emissions.

Note the word "potential." A diesel-electric propulsion system introduces several components into the system not seen in conventional marine installations, and each of these additional components comes with a cost in efficiency (after all, none are 100 percent efficient). All components must be carefully matched. The potential fuel savings are huge, but that will only happen with a proper design.

Today, two designs arguably lead the pack in practical applications: Glacier Bay and Steyr. The Glacier Bay system, used in the new Moorings 4300, uses their generator sets in conjunction with carefully selected motors and control components. The system has the propellers and electric motors completely decoupled from the diesel generators. A modest battery bank provides several hours of operation under battery power alone.

Typical operations use battery power to leave the dock and maneuver out to the course line. Then the generator is fired-up to both propel the craft and recharge the batteries. Fuel savings are realized by carefully matching the generator output to the power required to drive the craft at the desired speed.

The Steyr Motors solution features a motor/generator and clutch attached to the output end of the diesel. This motor-generator can be used as an electric motor to drive the propeller and even start the diesel, eliminating the need for a starter motor. The diesel can be used to drive the generator to charge the batteries. It can also charge the batteries while powering the propeller shaft.

ISLAND PILOTAn drawing of an overhead view of the Island Pilot Hybrid DSe highlighting the 6-kilowatt solar array.ADD IN SOLAR

One of the most unique applications of diesel-electric propulsion, with hybrid features, is the Island Pilot Hybrid DSe. The catamaran design is 39-feet, 6-inches with a 17-foot beam, and total displacement is about 17,500 pounds. This vessel was designed from the ground up to utilize both solar technology and the Steyr Motors Serial Hybrid Propulsion System.

For this application the Steyr unit consists of a 75 hp Steyr diesel engine connected to a combination electric motor/generator, which drives a ZF sail drive unit with a 3-blade bronze propeller. Each hull of the catamaran houses an engine, motor/generator a sail drive and a battery bank. Each battery bank consists of 10 Odyssey AGM batteries for a total of 20 batteries.

But what really sets this design apart, both visually and operationally, is the 6 kilowatt solar array. Virtually every flat surface of the vessel is covered with solar cells. The output of this solar array is sufficient to drive the vessel at about 5 knots for as long as the sun holds out. In this mode, the diesel engine is declutched from the electric motor and sail drive, allowing the electric motor to power the craft with the engine off. On the hook, the solar array is used to charge the batteries. Given good weather, the cruising range of the Island Pilot is virtually unlimited.

In weather unsuitable for solar operations, the diesel engine is fired-up. It drives the electric motor as a generator, charging the batteries. At the same time the engine also powers the sail drive providing speeds of about 7 knots at about 10 nautical miles to the gallon.

The DSe styling is unique, to say the least. Some like it, some don't. I'm a form follows function kind of guy and so I like the design. Note too that this is not a stripped out, bare bones boat. Every attempt was made to design the interior spaces to the highest standards. Standard equipment includes an induction cook top, a 14-cubic-foot refrigerator, a built-in microwave, washer/dryer, two Sealand VacuFlush toilets, four-zone air conditioning and an entertainment center.

Others must also think highly of this propulsion system. The Steyr hybrid solution won an innovation award at the 2008 IBEX show in Miami. In 2009, it won both the Pitman Innovation Award from SAIL magazine and the Best of the Year award from Motor Boating Magazine.

ISLAND PILOTA deck level view of the DSe solar array.ADDITIONAL BUILDERS

Several other builders have diesel-electric models in the works. The Lagoon 420 Hybrid Catamaran is currently available. This design has a unique feature: the propellers drive the generators when the boat is under sail. This technique, called "regenerations," converts wind energy into battery power by using the forward motion of the boat to turn the props.

The North Coast Power Yacht design by Michael Kasten had been created around traditional diesel propulsion. The Kasten design firm has just completed redesigning the vessel and is offering a diesel-electric propulsion option for new builds.

Also, the Moorings 4300 Hybrid Catamaran, which uses the Glacier Bay system, is now in charter at The Moorings. Chartering one would be a great introduction to the operational aspects of a hybrid propulsion system in real life.

Of course, there is always a downside somewhere, and diesel-electric systems are no different. First of all, these systems are relatively new in the recreational market and the learning curve for boat builders may be high. There are also more complicated systems, often with more parts to maintain.

Cost is also a factor. Estimates range from 125 percent to 150 percent of the cost of traditional diesel power. There is no question that a properly designed and installed diesel-electric propulsion system will save in fuel costs – but you will pay for it up front.

Then again, I'm certain that these systems will become more and more popular as the designs mature – and the costs will eventually come down.