In foggy conditions, a vessel should sound how many prolonged blasts followed by short blasts to signal its presence?

In foggy conditions, the correct signaling method for a vessel is to sound two prolonged blasts followed by two short blasts. This is a specific requirement outlined in the International Regulations (COLREGs) for vessels operating in reduced visibility. The two prolonged blasts indicate the presence of a power-driven vessel underway, which helps ensure that nearby vessels are aware of your location when visibility is compromised. The addition of two short blasts serves to further clarify the vessel's presence and intentions, enhancing situational awareness for others navigating in the same area. This sequence of signals is crucial for preventing collisions and ensuring safety on the water.