What does a vessel do to signal that it is altering its course?

A vessel signals that it is altering its course by making a short blast signal. This practice is part of the navigational rules defined in the COLREGs, which are designed to promote safe navigation and communication between vessels.

When a vessel emits a short blast, it indicates an intention to maneuver, such as altering course to starboard (to the right). This sound signal is crucial in preventing misunderstandings between vessels, especially in situations where visibility may be limited.

The other methods listed do not convey the same specific message regarding course alterations. Flashing lights and changing the color of navigation lights are not standardized signals for altering course; they serve different purposes, such as indicating distress or conveying other navigational information. A single long blast generally signifies a different action, such as indicating that a vessel is departing or that there is a need for caution in a crossing situation.