Collision requirements (colregs) require you have certain lights on during low visibility times like at night or in a fog. The running lights change based on if you are under power as well. Under sail, a boat is allowed to conserve energy by running a minimal set of lighting. The lights involved are the anchor, steaming, side, and stern. Masthead light is an ambiguous term I will avoid.
The anchor light lies at the top of the mast or tallest structure. The light radiates all around, 360 degrees. For a boat at anchor, the light is white. For a sailboat under sail, the light is tri-color. Under either scenario, the anchor light is the only light. Under power, a white all around anchor light combines with side lights for navigation.
The steaming light is halfway up the mast or tallest structure. She radiates white light forward 225 degrees. She does not radiate any colors. Use the steaming light solely under power combined with colored side lights and a stern white 135 degree light.
Side lights are a pair on each side towards the bow. Port is red, starboard green. Red means stop for a viewing vessel and yield to the red lighted vessel. You have the right of way aboard the red sighted boat. Green means the opposite. The viewing vessel has right of way, and the showing boat must yield. Under power, use the side lights with either a all-around anchor white light or the combination 225 degree steaming/135 degree stern whites.
The stern light is at deck level towards the boat’s transom. She is a white, 135 degree light. Under power, use her in combination with side lights and the steaming forward, 225 degree, white light. As a final twist under sail, a stern light combines with two anchor lights (one green, one red). The red light must be higher on the mast than the green light.
Navigation lights include the anchor, steaming, side, and stern lights. Depending on whether you are under power or sail or anchored, a boat shows different combinations of these lights. Generally, in each situation you need lights showing for all 360 degrees which penetrate 2 miles away. And when navigating, red means stop. Yield to a vessel showing red. No matter what be careful. Be a defensive sailor making sure you avoid peril.
Boat US provides the great animations below.
- Under Power
- Under Sail
|Click on “running lights.” See the combination of the given anchor, steaming, side, and stern lights needed for running under power. Note that another option includes an all around anchor light with no stern light. See the description pictures.||
|Click on the “running lights.” Portside is the same as for power boats under power. Starboardside-top is the setup for under sail. Note another option is a tri-color anchor light with given green, red, and white orientations.||