The red-over-green all-round lights at or near the masthead are in addition to the normal sidelights and sternlight, which must be shown. But the optional "tricolor" light at or near the masthead is in lieu of the normal sidelights and sternlight, which must not be shown if the tricolor light is lit.
Remember: A vessel with sails up, but also being propelled by machinery, even a small outboard motor, must show the lights of a power-driven vessel, not those of a sailing vessel. The tricolor light cannot be used in this situation. A white forward "masthead" light must be shown. The Inland Rules exempt a sailboat less than 12 meters from the requirement to show a cone, point downward, when under sail and power during daylight, there is no exemption in the International Rules.
It is desirable that a sailboat less than 7 meters in length show normal running lights, but she may alternatively show a white light, such as a flashlight or electric lantern shown on the sails, this is effective in making known the small craft's presence.
A rowboat will normally just show a white light in the direction of another vessel, or it could show the same lights as a sailboat.
A vessel proceeding under sail when also being propelled by machinery shall exhibit forward where it can best be seen a conical shape, apex downwards. A vessel of less than 12 meters in length is not required to exhibit this shape, but may do so.
A sailing vessel underway shall exhibit: sidelights and a sternlight. A sailing vessel of less than 20 meters in length the lights prescribed in this Rule may be combined in one lantern carried at or near the top of the mast where it can best be seen.
A sailing vessel underway may, in addition to the lights prescribed in this Rule, exhibit at or near the top of the mast, where they can best be seen, two all-round lights in a vertical line, the upper being red and the lower Green, but these lights shall not be exhibited in conjunction with the combined lantern permitted by paragraph (b) of this Rule.
A sailing vessel of less than 7 meters in length shall, if practicable, exhibit the lights prescribed in this Rule, but if she does not, she shall have ready at hand an electric torch or lighted lantern showing a white light which shall be exhibited in sufficient time to prevent collision.
A vessel under oars may exhibit the lights prescribed in this rule for sailing vessels, but if she does not, she shall have ready at hand an electric torch or lighted lantern showing a white light which shall be exhibited in sufficient time to prevent collision.
