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Rule 28: Vessels Constrained by Their Draft (COLREGS)

Last reviewed October 21, 2026

The short answer

Rule 28 lets a vessel constrained by her draft show, in addition to her power-driven lights, three all-round red lights in a vertical line, or a cylinder by day. It's an International rule only. Inland Rule 28 is reserved, so there's no constrained-by-draft signal on U.S. inland waters.

The rule text

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.

International Rules, U.S. Coast Guard Navigation Rules and Regulations Handbook (NAVCEN, 2024 corrected edition), Rule 28

§ 83.28 [Reserved]

Inland Rules, 33 CFR Part 83 (eCFR), Rule 28

What it means on the water

  • Three all-round reds in a vertical line, or a cylinder (Rule 28).
  • Shown in addition to the Rule 23 lights.
  • The term is defined in International Rule 3(h): a power-driven vessel severely restricted in her ability to deviate from her course because of her draft.
  • Other vessels (except NUC and RAM) avoid impeding her safe passage (International 18(d)).

International vs Inland

International only. Inland Rule 28 and Inland 3(h) are reserved.

Common exam traps

  • Using the cylinder on Inland waters.
  • Thinking she's NUC. NUC is two reds (Rule 27).

Try 3 questions on Rule 28

  1. Day shape for a vessel constrained by her draft?

    1. Ball
    2. Cylinder
    3. Diamond
    4. Two cones
    Show answer

    B. Cylinder Rule 28.

  2. Night lights, in addition to Rule 23?

    1. Two all-round reds
    2. Three all-round reds in a vertical line
    3. Red-white-red
    4. Green over white
    Show answer

    B. Three all-round reds in a vertical line Rule 28.

  3. Does Rule 28 apply on Inland waters?

    1. Yes
    2. No, Inland Rule 28 is reserved
    Show answer

    B. No, Inland Rule 28 is reserved 33 CFR 83.28 is reserved.

Frequently asked questions

What does three red lights in a vertical line mean?

A vessel constrained by her draft, under International Rule 28.

Is constrained by draft in the Inland rules?

No. Inland Rules 3(h), 18(d), and 28 are reserved.

Who must avoid impeding her?

Any vessel other than NUC or RAM, if circumstances admit (International 18(d)).

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