Question 33 GLI05 - Master or Mate of LT 200 GRT

The Correct Answer is B. ### Explanation for B (67.5°) The rule regarding the positioning and arc of visibility for the stern light is defined in the **COLREGs (International Regulations for Preventing Collisions at Sea)**, specifically Annex I, Section 9 (Horizontal sectors). This rule applies universally to both international and inland waters that adopt COLREG standards. The definition of a stern light is given in Rule 21(d): > "Stern light" means a white light placed as near to the stern as practicable showing an unbroken light over an arc of the horizon of **135 degrees** and so fixed as to show the light **67.5 degrees** from right aft on each side of the vessel. Therefore, the stern light shows from dead astern up to 67.5 degrees on the port side and 67.5 degrees on the starboard side, totaling an arc of 135 degrees. ### Why the Other Options are Incorrect **A) 22.5°** This angle (22.5°) is the standard arc for sidelights (red or green) *beyond* the standard 112.5° forward arc. Sidelights are fixed to show from dead ahead to 112.5° on their respective side, but the visibility is sometimes extended slightly to ensure overlap with the masthead light's full 225° arc. However, 22.5° alone has no direct relevance to the stern light's arc of visibility. **C) 112.5°** This is the required arc of visibility for the **sidelights** (red and green lights). Each sidelight shows from dead ahead to 112.5° aft on its respective side. It is not the arc for the stern light. **D) 135.0°** This is the **total** required arc of visibility for the stern light (67.5° + 67.5°). The question asks for the degree measurement "on **each side** of the stern," which is half of the total arc, or 67.5°.