🔍 Key Concepts

• Effect of a single operating screw when a twin-screw vessel is moving astern • How propeller side-force (transverse thrust) changes between ahead and astern • Which way a stern tends to swing versus which way the bow (head) appears to swing

💭 Think About

• First, imagine each screw working astern by itself with rudders amidships. Which way would the stern move for a port screw going astern? For a starboard screw going astern? • Then think: when the stern moves one way, how does that make the bow (vessel’s head) appear to move? • Compare the effect when both screws are working astern to when only the port screw is working astern and the starboard screw has stopped.

✅ Before You Answer

• Be clear on which propeller is still turning — only the port or only the starboard? • Remember that the question asks about the vessel’s head (bow), not the stern. • Recall that astern propulsion often reverses the normal transverse thrust direction you memorized for going ahead. Verify which way the stern (and therefore bow) will swing.