What is a primary responsibility for manned vessels concerning sound signals?

The primary responsibility for manned vessels concerning sound signals is to communicate with other vessels. This is crucial for navigational safety, especially in situations where visibility is poor, such as fog or heavy rain. Sound signals serve as a vital means of conveying information about a vessel's intentions, position, and movements to others nearby, helping to prevent collisions and ensuring smooth navigation in crowded or navigationally challenging waters.

The use of sound signals is governed by the International Regulations for Preventing Collisions at Sea (COLREGs), which outline the required sounds to be made in various situations, such as when a vessel is approaching a bend in a narrow channel, making turns, or signaling its presence in a specific manner. Sound signals, therefore, play a significant role in maritime communication and safety.

The other options do not align with the primary responsibility of sound signals: signaling a crew's readiness does not affect other vessels; ensuring silence while moored is not a communication method and could lead to safety issues if there’s insufficient communication; and maintaining engine performance does not relate to sound signaling but rather to the operational state of the vessel.