The Massachusetts Boater Safety Handbook
The Official Boating Handbook of the Massachusetts Department of Natural Resources - Web Version
Table of Contents
Be on the lookout for the lights of other vessels when boating at night. Several types of lights serve as navigational aids at night. There are four common navigation lights.
Sidelights: These red and green lights are called sidelights (also called combination lights) because they are visible to another vessel approaching from the side or head-on. The red light indicates a vessel’s port (left) side; the green indicates a vessel’s starboard (right) side.
Sternlight: This white light is seen from behind or nearly behind the vessel.
Masthead Light: This white light shines forward and to both sides and is required on all power-driven vessels. A masthead light must be displayed by all vessels when under engine power. The absence of this light indicates a sailboat under sail.
All-Round White Light: On power-driven vessels less than 39.4 feet in length, this light may be used to combine a masthead light and sternlight into a single white light that can be seen by other vessels from any direction. This light serves as an anchor light when sidelights are extinguished.
Encountering Vessels at Night
When you see only a white light, you are overtaking another vessel. It is the stand-on vessel whether it is underway or anchored. You may go around it on either side.
When you see a green and a white light, you are the stand-on vessel. However, remain alert in case the other vessel operator does not see you or does not know the navigation rules.
When you see a red and a white light, you must give way to the other vessel! Slow down and allow the vessel to pass, or you may turn to the right and pass behind the other vessel.
Encountering a Sailboat at Night
When you see only a red light or only a green light, you may be approaching a sailboat under sail and you must give way. The sailboat under sail is always the stand-on vessel!