🔍 Key Concepts

• Double reduction gear trains and how power flows from the turbine (high‑speed shaft) to the propeller shaft • The difference between a pinion (small driving gear) and a gear/wheel (larger driven gear) in each reduction stage • How double helical (two half gears) on the same shaft form one functional gear in marine reduction gears

💭 Think About

• Trace the power path: which small gear on the turbine shaft drives which larger gear, and then which smaller gear drives the large bull gear on the propeller shaft? • Look at which component labeled II is physically meshing with the small gear on the separate shaft—does that make it part of the first or the second reduction stage? • Notice that I and II are two halves of a double‑helical unit on the same hub: in a typical double reduction layout, what is that combined unit usually called?

✅ Before You Answer

• Confirm whether component II is on the same shaft as III, and how that affects whether it belongs to the first or second reduction stage • Identify which gear (IV, the big bull gear) is on the low‑speed/propeller shaft, then decide if II is upstream or downstream of that • Verify that a pinion is the smaller gear in a mesh and the term gear (or wheel) is used for the larger member in that same mesh