28Vessels Constrained by Their Draught
1The rule in plain words
A vessel constrained by her draft may, in addition to Rule 23 lights for power-driven vessels, exhibit three all-round red lights in a vertical line or a cylinder.
What may she exhibit?
In addition to the lights prescribed in Rule 23 for power-driven vessels, she may show three all-round red lights or a cylinder.
Where and how?
The three lights must be exhibited where they can best be seen, in a vertical line.
Who can be constrained by draft?
Rule 28 uses lights for power-driven vessels; see Rule 3(h): only a power-driven vessel can be constrained by draft.
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
Constrained by draft → an extra display is permitted.
- 2
Rule 23 lights for power-driven vessels remain the reference.
- 3
Red signal: three all-round lights · vertical line.
- 4
By day: a cylinder where it can best be seen (day shape).
4Frequent mistakes
Wrong: "The red lights replace the Rule 23 lights."
Right: No: they are exhibited in addition to the lights prescribed in Rule 23.
Wrong: "The three lights are side by side."
Right: They form a vertical line and are shown where they can best be seen.
Wrong: "A sailing vessel can be constrained by her draft."
Right: Rule 3(h) identifies a power-driven vessel as the vessel that can be constrained by her draft.
5Exam keys & interpretation
Exam keys
- "In addition to" means the Rule 23 lights stay; the three red lights do not replace them.
- Spot all three cues: three, all-round red, vertical line; missing one changes the answer.
- "Or a cylinder": three red lights at night, the cylinder by day (Rule 20).
How to read it
- Read "may" as permission, not an instruction that every vessel constrained by draft must always display the three lights.
- Use Rule 3(h) to identify the vessel; Rule 28 tells you what additional display she may exhibit.
6Official text
IMO COLREG 1972U.S. Coast Guard — International Navigation Rules (2024)
Full wording of the rule, reproduced from the official source below.
A vessel constrained by her draft may, in addition to the lights prescribed for power-driven vessels in Rule 23, exhibit where they can best be seen three all-round red lights in a vertical line, or a cylinder.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.
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