R of R Basics ------ Page 6 of 10
White masthead lights have an arc of visibilty of 225 degrees forward.
With only one masthead light on vessels under 50 meters in length, it is often difficult to visually determine when they make a course change.
It can often take 3 minutes or more to detect course or speed changes in target echo trails on radar.
Larger vessels have two masthead lights with the forward masthead light lower than the rear higher masthead light.
As shown here, two lights make it easy to immediately detect their course changes.
