🔍 Key Concepts

• Direction of rotation through a gear train (driving vs driven gears, and number of gear meshes) • Relationship between high-pressure (HP) and low-pressure (LP) turbine pinions to the main reduction gear • Effect of a right-hand turning propeller and astern steam admission on which elements must reverse direction

💭 Think About

• Trace the rotation starting at the astern turbine element on the HP side: if that pinion turns one way, which way must the next gear in mesh turn? Continue step by step through the train. • Compare the path and number of gear meshes on the HP astern side with the LP ahead/astern side. Does an even or odd number of meshes make the final pinions rotate the same or opposite directions? • Since the propeller is right-hand in ahead, what direction must the main shaft and low-speed gear rotate for sternway, and how does that constrain the HP high-speed gear’s rotation when on astern steam?

✅ Before You Answer

• Carefully count the number of gear meshes between the HP astern element and the main (low-speed) gear, and between the LP elements and the main gear. • Confirm which gears share the same shaft (and therefore same direction) versus which are only in tooth contact (and therefore opposite directions). • Verify that your final statement about the HP high-speed gear’s direction is relative to the specified viewpoint: "as viewed from the aft end of the reduction gear."