Re: Rule 23a question
Under rule 23 (a) a separate stern light is required.
Navigation Rules Online
Rule 23 - Power-driven Vessels Underway
(a) A power-driven vessel underway shall exhibit (click on icon to see picture
(i) a masthead light forward;
(ii) a second masthead light abaft of and higher than the forward one; except that a vessel of less than 50 meters in length shall not be obliged to exhibit such a light but may do so;
(iii) sidelights: and
(iv) a sternlight.
BTW - a masthead light is 225 degrees
Rule 21 - Definitions
(a) "Masthead light" means a white light placed over the fore and aft centerline of the vessel showing an unbroken light over an arc of the horizon of 225 degrees and so fixed as to show the light from right ahead to 22.5 degrees abaft the beam on either side of the vessel, except that on a vessel of less than 12 meters in length the masthead light shall be placed as nearly as practicable to the fore and aft centerline of the vessel.
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As I sail, I praise God, and care not. (Luke Foxe)