What action must a vessel take when it hears another's fog signal forward of its beam in thick fog?

When a vessel hears another's fog signal forward of its beam in thick fog, it is critical for safety that the vessel reduces its speed to the minimum required to maintain course. This action is necessary because it allows the navigating vessel to maintain control while remaining vigilant for the presence of other vessels that may not be visible due to the fog. Reducing speed minimizes the risk of collision, as the vessel can better assess its surroundings and react appropriately to any unexpected encounters.

This approach aligns with maritime safety protocols during poor visibility conditions, emphasizing caution and preparedness in navigating through areas where other vessels may be present but not sighted. In addition to reducing speed, the vessel may need to sound its own fog signal to alert others to its presence, contributing to overall situational awareness.

Increasing speed or turning around immediately would increase the risk of collision or confusion, as the vessel may not have enough time to react or change course safely in such conditions. Thus, reducing speed is the best practice to ensure safe navigation and prevent accidents in limited visibility scenarios.