When must vessels display navigation lights?

Vessels must display navigation lights when they are away from the dock between sunset and sunrise to ensure visibility and safety on the water. This requirement is crucial because reduced visibility during nighttime can lead to collisions or accidents if vessels are not properly illuminated. The navigation lights help other boaters recognize the type and size of the vessel, indicating its position and direction of travel.

Displaying lights only at night or during sunny days would not provide sufficient safety measures in varying light conditions. Additionally, having the lights on only during daylight or just at night does not account for the entire period in which visibility might be low, such as during overcast conditions or in areas with reduced daytime lighting. Therefore, the requirement specifically emphasizes using navigation lights when a vessel is moving away from the dock after sunset and before sunrise, ensuring optimal safety for all waterway users.