The Next Big Thing Page 2

The Next Big Thing

Part 2: Because of their complexity, diesel-electric systems are heavy and take up a lot of space.

January 2005

 More of this Feature

• Part 1: Diesel-Electric
• Part 2: Diesel-Electric
• Part 3: Diesel-Electric
• Diesel-Electric For Smaller Craft?

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• Engines Index

 Elsewhere on the Web
• FAST Electric Yacht Systems

Engineers refer to the energy required by these auxiliary systems, ranging from air conditioning to high-tech cinema setups, as “hotel load.” On most yachts this figure is a fraction of what is required to actually propel the boat. On warships, cruise liners, and, in this case Octopus, hotel loads either approach or exceed what’s required to move the boat. In the case of Limitless, however, the reasons for using diesel-electric power go deeper.

Limitless doesn’t require nearly as much auxiliary power as she does propulsion power. Therefore she employs a hybrid system that utilizes both straight diesel inboard drives and diesel-electric drives to deliver a whopping 22,000 hp and a reported top speed of 27.5 knots. According to Capt. Craig Tafoya, Limitless’ project manager, “It is this top speed that mandated the use of diesel-electric. Conventional diesels [that could achieve this speed] were so high strung that, when [at] idle speed [they] would never let us go below 16 knots. The diesel-electric option allowed for precision control while maneuvering (once the primary diesels were disengaged) and provided us with redundancy—we had backup propulsion if the main engines were lost.” Such redundancy is a huge advantage for any yacht using diesel-electric. In an emergency the output from any number of gensets can be combined to supply propulsion to electric motors to get you home.

But all this comes at a price. Because of their complexity, diesel-electric systems are heavy and take up a lot of space. Vripak International, a Dutch naval architecture firm, estimates the average weight penalty at two to five percent more than a conventional system, due to the additional gensets, electric motors, and frequency converters. However, diesel-electric does provide flexibility in engine and genset placement. The engines no longer have to be inline with the shafts, and gensets, and converters can be placed virtually anywhere. This ability to position equipment at the designer’s (and owner’s) discretion has significant advantages when it comes to trim characteristics of the boat and the spaciousness of guest quarters. No longer does the engine room have to occupy that critical space amidships where the beam is widest, and heavy components can be positioned to achieve optimum running angle.

Next page > Part 3: So which yachts could benefit from diesel-electric? Well, the larger the better. > Page 1, 2, 3, 4

This article originally appeared in the January 2005 issue of Power & Motoryacht magazine.

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