What signal should a vessel make when stopped and making no way?

When a vessel is stopped and making no way, it should make a prolonged blast of the whistle. This signal is important as it communicates to other vessels nearby that it is not underway and could potentially become a hazard if not appropriately noted. The prolonged blast serves as a warning because it alerts other vessels to your presence and your status.

This is particularly relevant in situations where visibility is limited, such as in fog or inclement weather, where vessels may not be able to visually identify your status. Two short blasts or a single short blast would indicate different maneuvers or intentions which do not apply to a vessel that is completely stationary. Not signaling at all could lead to confusion for nearby vessels, increasing the risk of a collision. Thus, the prolonged blast is a critical safety measure in maritime communication.