🔍 Key Concepts

• Ahead motion: Think about which way the water flows relative to the propeller when the vessel is moving ahead. • Face vs. back of the blade: One side pushes on the water (higher pressure), the other side has lower pressure (suction). • Pressure side vs. suction side: The pressure side is where the water is being pushed, not where it is being drawn from.

💭 Think About

• When the ship moves ahead, does the water move past the propeller from ahead to astern, or astern to ahead? Use that to define upstream and downstream. • Which side of the propeller actually "pushes" the water to drive the vessel forward—the side facing the incoming flow or the side facing where the water exits? • In propeller terminology, which name is usually given to the pushing side of the blade: face or back?

✅ Before You Answer

• Be clear on what upstream and downstream mean relative to water flow through the propeller during ahead motion. • Confirm which surface is commonly called the face and which is the back in marine propeller terminology. • Verify that the pressure side must be the surface where the water pressure is higher because the blade is doing work on the water, not the suction side.