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Rule 28: Vessels Constrained by Their Draught

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.

Rule 28 of 41

Decide

An interactive 3D illustration is shown here. The same content is described in the rule text and key takeaways below.

Decision 1 of 3

It is night and you see only these lights. What vessel is it?

The rule in plain words

  1. 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.
  2. Where and how?The three lights must be exhibited where they can best be seen, in a vertical line.
  3. 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.
Identification detail. A vessel constrained by draught may add three red all-round lights or a cylinder to its power-driven-vessel identification. This additional identification is optional.

Before you read on: what would you do?

Question 1/1

What may a vessel constrained by her draft exhibit in addition to the Rule 23 lights?

See it in 3D

Drag the vessel to turn it: 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.

Frequent 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.

Exam keys & interpretation

  1. "In addition to" means the Rule 23 lights stay; the three red lights do not replace them.
  2. Spot all three cues: three, all-round red, vertical line; missing one changes the answer.
  3. "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.

Key points

  • Constrained by draft → an extra display is permitted.
  • Rule 23 lights for power-driven vessels remain the reference.
  • Red signal: three all-round lights · vertical line.
  • By day: a cylinder where it can best be seen (day shape).

Test your knowledge

3 questions to check it. Pick an answer to see why.

Question 1/3

How are the three red lights arranged?

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Official text

IMO COLREG 1972 U.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:

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Reviewed by Ramon Curto, Nautical teacher at IECNPC · Last reviewed:

Frequently asked questions about COLREG Rule 28

What lights does a vessel constrained by her draught show?

Three all-round red lights in a vertical line, or a cylinder as a day shape, in addition to the lights prescribed for power-driven vessels in Rule 23. Rule 28 is permissive: the vessel may display these signals.

What is the day shape for a vessel constrained by her draught?

A cylinder. It is exhibited in addition to the normal power-driven vessel signals, not instead of them, and failing to recognise it is a common mistake.

How do constrained-by-draught lights differ from NUC or RAM lights?

The constrained-by-draught signal is three all-round red lights in a vertical line, shown on top of the Rule 23 power-driven vessel lights. Confusing it with the not-under-command or restricted-in-ability-to-manoeuvre signals is the classic Rule 28 error.