🔍 Key Concepts

• Rule 21 – Definitions of lights (masthead lights and sidelights) and what a green sidelight with two white masthead lights means about the vessel’s aspect • How your own heading (due south) and the bearing "one point on the port bow" place the other vessel on your southeast side • Relating what you see (the vessel’s starboard side) to which way that vessel’s bow must be pointing (NW, NE, SE, or SW)

💭 Think About

• From which side are you viewing the other vessel if you see a green sidelight and two white masthead lights in line? Starboard or port? Ahead or abaft the beam? • Given that you are heading due south and the target is one point on your port bow, where is that target on the compass around you (NE, SE, etc.)? • If you are looking at the vessel’s starboard side and that vessel is located slightly to your port of dead ahead, which of the four options (NW, NE, SE, SW) would have its starboard side facing you?

✅ Before You Answer

• Confirm that green = starboard sidelight and two white lights in line = power-driven vessel over 50 m, seen in a sector where both masthead lights are visible • Sketch yourself heading due south and mark a contact one point (11.25°) on your port bow to see which quadrant it lies in • For each choice (NW, NE, SE, SW), quickly imagine or sketch the other vessel’s heading arrow and check: would your position fall on that vessel’s starboard side within the sidelight sector?