Time to Look Again at Diesel-Electric

A Hollywood star, reflecting on the reality behind his “overnight stardom” mused that in his case, “overnight” had only taken 17 years to get to. Many of today’s remarkable “new” technologies are actually not new at all, but have either matured through a slow and steady development process, or perhaps have benefitted from a materials or software development that brought them along the final steps to the marketplace.

Diesel-electric propulsion for recreational boats may just fit this description. The concept is many, many decades old. In fact, depending on the exact definition you use, rather advanced applications were in place as long ago as World War I, when diesel-powered submarines re-charged battery banks for underwater electric propulsion.

Today, diesel-electric is dominating many big-ship applications, as in the cruise industry. It does so because of efficiency and reliability — two of the primary concerns in any commercial application. On a large cruise ship, the electrical demands are huge and varying. Large diesel generators come online as needed to generate electricity to meet both the hotel load as well as the propulsive requirements. When they come online they run constantly at their most optimum speed, which means they are efficient. These big cruise ships are powered by large electrically driven azimuthing pods, which add tremendous maneuverability to the equation, in addition to efficient propulsion.

For the recreational boater, diesel-electric systems traditionally were too big, too heavy, and too expensive for most to consider. Until now. Glacier Bay’s OSSA Powerlite product line now includes complete diesel-electric systems for recreational boats of most sizes. The best application of these new systems for now will be in new designs and new builds of certain existing designs; this in order to best take advantage of some of the unique features of these systems. It is conceivable that some boaters may also benefit from a re-power with an OSSA Powerlite system, depending on budget and performance objectives. I talked to the company recently at the Newport International Boat Show in Newport, RI.

In one of the first publicized applications, the charter company The Moorings had one of its Leopard 4300 sailing catamarans outfitted with an OSSA Powerlite diesel-electric system. The result, shown at the Miami Boat Show, was a tremendously efficient and quiet system that passed all its qualification tests with The Moorings and joined the charter fleet there.

In a completely different kind of application, a new 73′ Park Isle trawler, “Snowbird,” is being outfitted with a system featuring five 200Kw generators, two 800Hp motors and four 35Hp motors (for thrusters and stabilizers). Park Isle confirms this week that the power system is being delivered by OSSA Powerlite right now and they expect to complete construction of this boat shortly.

And since nature apparently favors symmetry and complete circles, there is even an OSSA Powerlite system installed in a recreational submarine (yes, there are such things; an article on them in an upcoming issue of Ocean Lines).

At the outset, I mentioned that often an old idea, like diesel-electric propulsion, benefits from new process or materials. This is the case with the OSSA Powerlite systems. For example, only two years ago, the lightest 200Kw generator you could get weighed over 4,000 pounds. The new OSSA Powerlite 200Kw generator comes in at around 1,400 pounds wet. In addition, the new electric motors designed and built by OSSA Powerlite approach 99% efficiency in converting the electricity generated by the diesel into horsepower on the shaft. And without a transmission to go through, that horsepower goes right to the propeller. The torque curve, typical for a DC electric motor, is also completely flat throughout the RPM range, which translates into powerful, linear acceleration.

Cost is still a factor, as even OSSA Powerlite reps will admit, but it becomes less so if the boat is designed to take advantage of diesel-electric from the outset, and even less of a consideration when the net present value of fuel savings is taken into account. For a new yacht build, the cost premium is about 5% of the purchase price, according to OSSA Powerlite sales managers. A re-power might come in anywhere from breakeven to 100% more expensive, again before operating efficiency gains are calculated.

There is another significant advantage of a diesel-electric propulsion system. In a conventionally powered boat, the diesel engine, its transmission and shaft to the propeller are the big weight “problems” in boat design. Typically, they can only be placed within a limited space and dictate placement of all the other systems around them. In a diesel-electric system, the generator needs to be connected to the drive motor only by electrical cabling. This means the heavy diesel can now be part of the weight and balance “solution” rather than just the “problem” around which the rest of the boat must be designed. The diesel generator can go wherever it best suits the designer’s needs. That’s a lot of flexibility.

There does appear to be a place for true diesel-electric systems like those of OSSA Powerlite in the recreational boating market. As the emphasis on fuel efficiency and comfort continues to grow, with more and more Baby Boomers buying upscale power boats, we should see more of these systems.

And down the road a bit (apologies for the highway metaphor here), we will undoubtedly see continuing development of these systems, with the electric motors moving outside the hull into azimuthing pod drives, just like in the big cruise ship applications. Electric pod drives are where we all will end up, and probably sooner rather than later. Seeing what they’ve already done, my guess is that OSSA Powerlite will be there first in the recreational boat market. Take a look at them at:

www.OSSAPowerlite.com .

Copyright © 2007 Thomas M. Tripp

Posted by Tom

Tom Tripp is the owner of OceanLines LLC, the publisher of OceanLines and founder of Marine Science Today. He is an award-winning marine journalist, science writer and long-time public communications specialist. His PR career and much of his writing stems from the fact that he loves to explain stuff. It all began when he and his brother Mark threw all of Mom's tomatoes at the back wall of the house. . .