How far back can the light of a masthead light be seen?

The visibility of a masthead light is a crucial element in navigational safety, especially for vessels operating at night or in low visibility conditions. A masthead light is required to be visible from directly ahead and includes a certain angle of visibility.

A masthead light is typically visible over an arc of 225 degrees from the front of the vessel, meaning that it can be seen by an approaching vessel within that range. However, it primarily serves vessels that are approaching from the front and thus, the standard visibility for the purposes of navigation regulations specifically specifies that the light is visible within an angle of 22.5 degrees off each side of the centerline, adding to the 180 degrees forward arc.

This understanding aligns with the requirements set forth by the applicable maritime rules which designate how vessels should display their lights to communicate their presence and direction of travel effectively. The 22.5-degree visibility is a standard measurement used in these regulations, defining the effective range at which a vessel can see the masthead light and ascertain the operational characteristics of another vessel.