21
Definitions (Lights)
Defines masthead light, sidelights, sternlight, towing light, all-round light, flashing light, and special flashing light.
Rule 21 defines the types of navigation lights:
a
Masthead light: white light over an arc of 225 degrees, visible from dead ahead to 22.5 degrees abaft the beam on both sides
b
Sidelights: green light on starboard side and red light on port side, each showing over an arc of 112.5 degrees from dead ahead to 22.5 degrees abaft the beam
c
Sternlight: white light over an arc of 135 degrees, shown from dead astern to 67.5 degrees on each side
d
Towing light: yellow light with the same characteristics as the sternlight
e
All-round light: a light showing over an arc of 360 degrees
f
Flashing light: a light flashing at regular intervals at a frequency of 120 flashes or more per minute
Key Takeaways
1
Masthead light covers 225 degrees (ahead to 22.5 abaft beam)
2
Sidelights cover 112.5 degrees each
3
Sternlight covers 135 degrees
4
All-round light covers full 360 degrees
Common Mistakes
Confusing the arcs of visibility for different light types
Forgetting towing light is yellow, same arc as sternlight
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