🔍 Key Concepts

• Helical reduction gears and how their teeth engage compared to straight-cut (spur) gears • The effect of multiple teeth in mesh at the same time on vibration, noise, and load sharing • Purpose of a reduction gear in a propulsion train (relationship between input speed/torque and output speed/torque)

💭 Think About

• Ask yourself: When more than one tooth is sharing the load at the same time, what happens to how smoothly power is passed from one gear to the other? • Think about what a reduction gear normally does to speed and torque. Does it turn high speed into heavy load, or heavy load into high speed? • Consider whether the shape and engagement of gear teeth can realistically eliminate propeller shaft end thrust, or if that is handled by another component in the shafting system.

✅ Before You Answer

• Verify what a reduction gear is designed to do: change speed vs. change direction of thrust. • Check which choice directly relates to smoother transmission of power and reduced shock/vibration when teeth come into and out of mesh. • Confirm whether end thrust is normally controlled by thrust bearings rather than by the design of gear tooth engagement.