In fog with nothing on radar, upon hearing a fog signal forward, what must a vessel do?

In fog conditions where visibility is severely reduced, the primary concern for vessels is safety for themselves and others. When a vessel hears a fog signal forward, it indicates the presence of another vessel in proximity, which could pose a collision risk. Therefore, the appropriate response is to reduce speed or slow to bare steerageway.

This action allows the vessel to maintain better control while being able to maneuver if necessary. It also helps in minimizing the risk of collision due to the limited visibility and the uncertainty of other vessels' actions and positions. Keeping a safe speed is essential in foggy conditions, as it provides adequate time to react to sudden developments, such as another vessel appearing unexpectedly. Reducing speed also enables the crew to listen more carefully for sounds that might indicate nearby vessels, further enhancing safety.

Maintaining current speed or sailing at full speed could lead to dangerous situations, as it reduces the time needed to respond to the presence of other vessels and increases the likelihood of a collision. Taking no action would also be inappropriate, as it overlooks the need to be proactive in a situation where navigation is compromised by fog.