In a message dated 10/16/04 12:04:27 AM, Mike Schooley writes: << Actually, I think you have the gears in the wrong system. The engine usually requires a gear box to reduce the maximum engine speed to match the maximum propeller speed, so the comparison should be engine/gear box/propeller shaft versus engine/generator and electric motor/propeller shaft. The gear box will typically be 98% to 99% efficient whereas the generator/motor combination is only ~90% efficient. >> Mike, The FAST system uses gears at both ends. The diesel engine is coupled to a gearbox which contains several miter geared right angled drives. Alternators are attached to these drives like grapes on a grape cluster. The alternators are modular units of a standard size. Higher power is obtained by using a greater number of alternators. The output of each is controlled by a microprocessor. The generated electricity drives propulsion motors also attached to a gearbox to reduce the rpm to propeller speeds. So gears and alternators attached to the diesel, motors and gears attached to the prop all to get the power from the engine to the propeller. As I said, Rube Goldberg would have been proud. Your estimate of the efficiency of components is probably too high. Gearboxes are rarely 98 to 99% efficient unless made with watchmaker precision. Marine engineers usually estimate a driveline efficiency of 95%. That's why gearboxes get hot and oil coolers are necessary. Exposed roller chains are messy. In the early 1900s shaft driven bicycles were introduced using a right angled gearset at the pedals and a smaller right angled gearset at the rear wheel. Both gears and shafts could be enclosed in protective housings shielded from the elements. The bicycles never caught on because the power losses of two gear drives were unacceptable in a human propelled vehicle. Messy though it was, the roller chain drive was far more efficient than gears. (Although BMW revived the idea 50 years later for motorcycles.) In a similar vein, small generators and motors are less efficient than large units. Most auxiliary generators rarely have efficiencies higher than 85%. A 95% efficient motor capable of outputting power at propeller speeds is usually the size and weight of a Volkswagen. There are many reasons for using diesel/electric drives in boats and locomotives but efficiency (and fuel economy) is not one of them. Regards, Larry Z