Some medium and high-speed diesel engines require reduction gear units to provide a useful propeller speed. In most reduction gears, the bull gear __________.
• Reduction gear trains in medium/high-speed diesel installations • Relationship between bull gear, pinion gear, and propeller shaft • Which component usually runs fast and which runs slow in a reduction gear
• Think about which shaft you want turning more slowly: the engine crankshaft or the propeller shaft? Then decide which gear will be attached to that slower shaft. • In a reduction gear set, does the largest gear usually turn faster or slower than the small driving gear? How does that relate to the propeller’s required RPM? • Consider what the main purpose of a reduction gear is. Which gear in the train will be associated with that reduced speed and increased torque?
• Identify which gear (bull or pinion) is the large, slow-turning gear. • Decide which shaft in the system actually drives the propeller in normal marine installations. • Check whether the bull gear is typically the driver or the driven member in a reduction gear arrangement.
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