What is a requirement for all vessels when navigating in restricted visibility according to Rule 19b?

In situations of restricted visibility, Rule 19b mandates that all vessels must have their engines ready for immediate manoeuvre. This requirement is critical because visibility limitations could quickly change navigational circumstances, such as encountering other vessels or navigating around hazards. Being prepared to maneuver demonstrates vigilance and responsiveness, enabling vessels to take prompt action to avoid collisions or navigate safely.

While it may seem advantageous to signal other vessels or maintain a steady course, such actions do not address the need for immediate readiness to react to unforeseen circumstances, which is the main focus of the requirement. Proceeding at maximum speed is also not safe, as this could increase the risk of a collision in limited visibility situations. Hence, the emphasis on having engines ready for immediate maneuvering is essential for maintaining safety and preventing collisions in these challenging conditions.