What should a vessel do if it hears a fog signal from another vessel ahead of her beam according to Rule 19e?

When a vessel hears a fog signal from another vessel ahead of her beam, according to Rule 19(e), the appropriate action is to reduce speed to the minimum necessary to stay on course. This rule emphasizes the importance of maintaining a safe speed when navigating in reduced visibility conditions, such as fog, where the risk of collision increases due to limited sight range.

Reducing speed allows for better reaction time and control over the vessel's movement, ensuring that if an encounter with another vessel occurs, there's adequate time and distance to respond safely. It is crucial for vessels to prioritize safety by maneuvering cautiously in challenging visibility situations instead of increasing speed or changing course suddenly, which could lead to hazardous situations and potential collisions.

Other options, such as changing course immediately or waiting for clearer visibility before taking action, may not effectively mitigate the risks present in foggy conditions. Moreover, increasing speed contradicts the core principle of Rule 19, which aims to reduce the likelihood of accidents. Thus, reducing speed to the minimum necessary is the most responsible and safety-oriented approach when encountering a fog signal from another vessel.