🔍 Key Concepts

• Input vs output shaft in a reduction gear – where power comes in from the engine and where it leaves toward the propeller • Typical location of the engine coupling and propeller shaft coupling in marine gearboxes • How the reduction gears sit between the input shaft and output shaft in the housing

💭 Think About

• Look at which numbered shaft is directly connected to the engine flywheel or clutch by a large flange – would that be input or output? • Trace the power flow: from the engine, through the reduction gears, to which shaft that finally exits the housing toward the propeller? • Which shaft passes through the main reduction gear train and leaves the housing on the side you’d expect the propeller shaft to be located?

✅ Before You Answer

• Identify which end of the drawing is the engine side (large driving flange) and which is the propeller side (tailshaft coupling). • Verify which numbered shaft is in line with the final driven gear (after reduction), not the first driven gear. • Confirm that the shaft you pick is the one that would connect to the propeller tailshaft, not to any auxiliary drive or clutch mechanism.