In shallow water, as depth under keel decreases, what happens to the diameter of the vessel's turning circle?

• A. Increases
• B. Decreases
• C. Remains the same
• D. Varies unpredictably

Answer: (A)

Turning a vessel relies on the sideways force the rudder can generate for a given speed and rudder angle. In shallow water, the bottom limits how water can move around the hull and rudder, increasing resistance and reducing the effectiveness of the rudder. With less turning moment available, the ship can’t swing as tightly and needs to travel farther to complete the same turn. The result is a larger turning circle diameter when the depth under the keel decreases.