Seaman's Handbook

PART C. Lights and Shapes : Sailing vessels underway, and vessels under oars

(a) A sailing vessel underway shall exhibit:
  1. sidelights;
  2. A sternlight.
(b) In a sailing vessel of less than 20 metres in length the lights prescribed in paragraph (a) of this Rule may be combined in one lantern at or near the top of the mast where it can best be seen.(c) A sailing vessel underway may, in addition to the lights prescribed in paragraph (a) of 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.(d)
  1. A sailing vessel of less than 7 metres in length shall, if practicable, exhibit the lights
    prescribed in paragraph (a) or (b) of this Rule, but if she does not, she shall have ready to
    hand an electric torch or lighted lantern showing a white light which shall be exhibited in
    sufficient time to prevent a collision;
  2. A vessel under oars may exhibit the lights prescribed in this Rule for sailing vessels,
    but if she does not, she shall have ready to hand an electric torch or lighted lantern
    showing a white light which shall be exhibited in sufficient time to prevent a collision.
(e) A vessel proceeding under sail when also being propelled by machinery shall exhibit forwards where it can best be seen a conical shape, apex downwards.