🔍 Key Concepts
• Rule 21 – Definitions of lights (masthead, sidelights, sternlight, towing light) and their arcs of visibility
• Standard arcs: sidelights = 112.5° from right ahead to 22.5° abaft the beam, stern light = 135° centered on dead astern, towing/yellow light = same arc as stern light
• How exam figures usually show the bow at the top of the box and stern at the bottom, so you can tell if the light is shining more forward or more aft
💭 Think About
• Look carefully at figure B: does the dark sector cover mostly the forward quadrant, mostly the aft quadrant, or is it centered around dead astern?
• Compare the width of that dark sector to 90°, 112.5°, and 135°. Which light(s) share similar arcs, and how does the direction the sector faces narrow it down?
• Think about which of the options would ever shine significantly forward versus only aft. Which does the drawing suggest?
✅ Before You Answer
• Verify which lights in the answer choices have identical arcs (for example, stern vs yellow towing light).
• Confirm from Rule 21 that sidelights extend from right (or left) ahead to 22.5° abaft the beam, not all the way to dead astern.
• Make sure you can identify on the figure where dead ahead and dead astern would be before deciding which light it represents.