When is it preferable for a vessel to alter course instead of speed?

Altering course rather than speed is preferable when it makes the vessel's intentions more obvious to other vessels. This is particularly important for collision avoidance. When a vessel changes course, its movement can be more visually perceptible to other navigators, providing clearer information about its direction and intention. In contrast, simply reducing speed may not convey enough information, especially if other vessels are also moving or if visibility conditions are poor.

In scenarios where visibility is limited, changing course can provide a definitive indication of a vessel's navigational intentions, thus assisting in promoting safety at sea. While the size of the vessel and its speed can factor into navigational decisions, the key principle is ensuring that other vessels can easily interpret the actions taken, which is achieved more effectively through a course alteration.