Rule 31 states that where it is impracticable for a seaplane or WIG craft to exhibit lights and shapes of the characteristics or in the positions prescribed in Part C, she shall exhibit lights and shapes as closely similar in characteristics and position as is possible.
IMO COLREG 1972Official text
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.An interactive 3D illustration is shown here. The same content is described in the rule text and key takeaways below.
Recognition Sequence
Classify the vessel state first: underway, making way, stopped, at anchor, aground, towing, fishing, pilotage or special condition.
Read special lights vertically from top to bottom before using sidelights and sternlight to confirm aspect.
Use the complete display and any vessel length stated in the scenario.
Optional second masthead lights, two anchor lights or deck illumination do not by themselves prove a minimum vessel length.
Exam Focus
Avoid identifying a vessel from one colour alone.
Many mistakes come from spotting a red light and guessing before checking the full pattern.
If the question mentions 'making way', 'underway but stopped', 'at anchor' or 'aground', that wording usually determines which extra lights or shapes appear.
Key Takeaways
Seaplanes must exhibit lights as similar as practicable to the rules
WIG craft are also covered by this rule
Practical limitations are acknowledged
Common Mistakes
Assuming seaplanes are exempt from showing navigation lights
Test Your Knowledge
Practise this topic and review the explanation for each answer.
More rules in this Part
- Fishing VesselsFishing vessels show green over white when trawling, red over white for other fishing, and sidelights plus sternlight when making way.
- Vessels Not Under Command or Restricted in Ability to ManoeuvreNUC shows two red all-round lights vertically. RAM shows red-white-red all-round lights vertically.
- Vessels Constrained by Their DraughtA vessel constrained by draught may display three all-round red lights in a vertical line, or a cylinder day shape.
- Pilot VesselsA pilot vessel on duty shows white over red all-round lights at the masthead. When underway, also sidelights and sternlight.
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