While underway in fog, you hear a vessel ahead sound two prolonged blasts on the whistle. You should __________.

Answer: B — sound only fog signals until the other vessel is sighted

When a vessel sounds two prolonged blasts on its whistle while underway in fog, it is signaling its intention to indicate that it is operating in the vicinity of other vessels. In this situation, sounding only fog signals continues to convey your presence to the other vessel until visual contact is established. This approach enhances safety, allowing for better navigational awareness in reduced visibility. It's essential to maintain communication through sound signals when visibility is limited, as these signals are part of the Rules of the Road that ensure vessels can understand each other's movements and intentions without visual cues. This method can be especially important in avoiding potential collisions or misunderstanding while navigating in foggy conditions. Other choices do not align with the established protocols for navigating in fog. Reducing speed, altering course to port, or to starboard might be actions taken in different scenarios, but they may not be appropriate without knowing the other vessel's exact position and intentions. Prioritizing the use of fog signals until the vessel is sighted is a precautionary measure that enhances safety in these complex situations.