A vessel under sail must display red and green sidelights, along with a sternlight (Fig. A).
Sail-driven vessels under 20 m in length have the option of displaying :
- Two all-round lights near the top of the mast (an all round red light over and all round green light). In addition to the green and red sidelights and stern light (Fig. B); or
- A tri-light at the top of the mast (in lieu of sidelights and a stern light) while underway between sunset and sunrise. A tri-light is divided into three sectors: a red light showing through a horizontal arc of 112.5degrees, a green light displayed through an arc of 112.5degrees, and a white light (to show across the stern) displayed through an arc of 135 degrees (Fig. C).
For non-powered vessels and/or sailing vessels that are under 7m in length the operator must have readily at hand a waterproof flashlight or lantern showing a white light so that an approaching boat can be signaled in time to avoid a collision. It is sometimes effective to use the light to illuminate the sail (Fig. D).
Navigation light options for sail boats are as follows: