31Seaplanes
1The rule in plain words
When a seaplane or WIG craft cannot show the prescribed lights and shapes, it must use ones as closely similar as possible.
When does it apply?
When it is impracticable for a seaplane or WIG craft to exhibit the prescribed lights and shapes, she shall exhibit similar lights and shapes.
Similar in what way?
They must be as closely similar as possible in characteristics and position to those prescribed in the Rules of this Part.
2See it in 3D
Turn the vessel or pick bow, stern, port or starboard: this is how her lights look at night.
An interactive 3D illustration is shown here. The same content is described in the rule text and key takeaways below.
3Key points
- 1
COLREG · Rule 31 → seaplane · WIG craft.
- 2
Trigger → prescribed display is impracticable.
- 3
Substitute → lights and shapes.
- 4
Test → closest possible match in characteristics + position.
4Frequent mistakes
Wrong: "If the prescribed display is impracticable, the vessel is exempt."
Right: It must exhibit lights and shapes as closely similar as possible.
Wrong: "Any alternative lights and shapes are acceptable."
Right: They must be as similar as possible in characteristics and position.
Wrong: "Rule 31 covers seaplanes, not WIG craft."
Right: It covers both a seaplane and a WIG craft.
5Exam keys & interpretation
Exam keys
- "Impracticable" means it cannot exhibit them, not that it simply chooses another arrangement.
- "Characteristics and position": the answer must address both, not just one.
- "As closely similar as possible" asks for the nearest match, not a random alternative.
How to read it
- Read it as a conditional adaptation: first the prescribed display is impracticable; then choose the closest possible match.
- Compare the substitute with what the Rules of this Part prescribe, in both characteristics and position.
6Official text
IMO COLREG 1972U.S. Coast Guard — International Navigation Rules (2024)
Full wording of the rule, reproduced from the official source below.
Where it is impracticable for a seaplane or a WIG craft to exhibit lights and shapes of the characteristics or in the positions prescribed in the Rules of this Part she shall exhibit lights and shapes as closely similar in characteristics and position as is possible.Source: U.S. Coast Guard — International Navigation Rules (2024)
Finish this unit
When you've read it, match the terms, then answer three questions. Get them all right to finish the unit; opening the page alone doesn't count.
My notes for this unit
No notes