🔍 Key Concepts

• Sternlight definition and purpose in the Navigation Rules (look in the section on lights and shapes) • The arc of visibility for masthead lights, sidelights, and sternlights and how they differ • Relationship between a full circle (360°) and the specific sectors assigned to different navigation lights

💭 Think About

• First recall which light is visible over the largest arc and which over a smaller arc: masthead light, sidelights, or sternlight? • Think about how many degrees the sternlight does NOT cover compared to a full 360° circle. How much of the circle is left for the masthead and sidelights? • Sketch a simple circle for the vessel, mark dead ahead (0°) and dead astern (180°), and then mark the sector that the sternlight should cover centered on 180°.

✅ Before You Answer

• Verify in the Navigation Rules, Annex I / Lights and Shapes, how the sternlight sector is defined in degrees from dead astern • Double-check that the sidelights each cover from dead ahead to 22.5° abaft the beam, and use that to reason what remains for the sternlight • Confirm that the correct answer is an angle measured on each side of dead astern, not the total arc of the sternlight.