🔍 Key Concepts

• Relationship between fixed-pitch propellers and engine reversibility • Typical speed class (slow vs medium) for large main propulsion diesels on big ships • How direction of rotation is changed for different propulsion setups (engine itself vs gearbox/CPP)

💭 Think About

• Ask yourself: when a ship has a fixed-pitch propeller and no reduction gearbox doing the reversing, how does it get astern thrust? • For the very largest ocean-going cargo ships and tankers, what general type of diesel engine is commonly installed: slow or medium speed? • Which combination of engine speed range and ability to reverse direction best matches direct drive to a fixed-pitch propeller?

✅ Before You Answer

• Identify whether a fixed-pitch propeller normally needs a reversing engine or can rely on controllable pitch to go astern • Recall that very large, direct-drive main engines are usually in the slow-speed category (check typical rpm ranges in your notes) • Eliminate any choice where the engine type would normally require a gearbox with clutch and reversing instead of being directly coupled to the shaft