What does the masthead light signify at night for a sailing vessel?

The masthead light on a sailing vessel at night indicates that the vessel is power-driven. This light is white and mounted at the top of the mast, and it is part of a set of navigation lights required for vessels to signal their status to others on the water. When a sailing vessel is under power, it displays the masthead light along with other appropriate lights, which differentiates it from a sailing vessel that is under sail (which typically will not display a masthead light if it is only sailing).

A sailing vessel that is under sail, for instance, would have its sidelights and sternlight displayed but not necessarily the masthead light unless it is also using an engine. This distinction is important for ensuring safe navigation and understanding the type of vessel operating in the area, as the presence of a masthead light clarifies that the vessel is using a motor rather than relying solely on wind power.