COLREGS Rule 28 — Navigation Lights
Vessel Constrained by Her Draft — Navigation Lights (COLREGS Rule 28)
A vessel constrained by her draft (CBD) may show three all-around red lights in a vertical line and a cylinder dayshape, in addition to the normal lights of a power-driven vessel. These are optional, not mandatory. CBD status applies only to power-driven vessels under COLREGS — there is no equivalent category in the US Inland Rules.
Condition: Power-driven vessel severely restricted in ability to deviate from her course due to draft in relation to available depth — COLREGS waters only
Navigation lights required
| Light | Color | Arc | Position |
|---|---|---|---|
| All CBD lights shown IN ADDITION TO Rule 23 power-driven vessel lights | — | — | See Rule 23 power-driven underway lights (masthead, sidelights, sternlight) |
| All-around red light (top) | Red | 360° | Top of three vertical all-around red lights |
| All-around red light (middle) | Red | 360° | Middle of three vertical all-around red lights |
| All-around red light (bottom) | Red | 360° | Bottom of three vertical all-around red lights |
All CBD lights shown IN ADDITION TO Rule 23 power-driven vessel lights: CBD lights supplement Rule 23 lights — they do not replace any of them
All-around red light (top): Optional — vessel MAY show these lights; they are not mandatory
All-around red light (middle): Optional
All-around red light (bottom): Optional
Dayshapes
| Shape | Position | When displayed |
|---|---|---|
| Cylinder | Where it can best be seen | Optional dayshape for a vessel constrained by draft during daylight — COLREGS only |
Exceptions and size rules
- →CBD lights and dayshape are OPTIONAL (permissive) — a vessel constrained by draft MAY show them, but is not required to.
- →CBD applies ONLY to power-driven vessels — not sailing vessels or any other vessel type.
- →CBD does NOT exist under US Inland Rules — it is a COLREGS-only status.
Inland Rules differences
- !The constrained-by-draft category does not exist in the US Inland Rules. Inland vessels operating in shallow water use no special lights or dayshapes for draft restriction.
Common exam mistakes
- ✗Thinking CBD lights are mandatory — they are permissive; the vessel may show them but is not required to.
- ✗Applying CBD status in US Inland Rules waters — CBD only exists under the 72 COLREGS.
- ✗Confusing three vertical red lights (CBD) with two vertical red lights (NUC) or red/white/red (RAM).
- ✗Applying CBD status to a sailing vessel — under Rule 3, constrained by draft applies only to power-driven vessels.
USCG exam questions — Vessel Constrained by Her Draft
These questions are drawn from the same pool used in real USCG licensing exams. Correct answers and explanations are shown.
1. A vessel 'constrained by her draft' as defined in Rule 3(h) applies to:
- A.A power-driven vessel which, because of her draft in relation to the available depth and width of navigable water, is severely restricted in her ability to deviate from the course she is following✓
- B.Any vessel whose draft exceeds 10 meters
- C.Any vessel that is heavily laden to the point where her freeboard is less than 0.5 meters
- D.Both power-driven and sailing vessels navigating in charted shallow water areas
Why: Rule 3(h) defines CBD as applying only to power-driven vessels whose draft in relation to available depth severely restricts their ability to deviate from their course — this is a COLREGS-only category not found in the Inland Rules.
2. A vessel constrained by her draft may exhibit which optional lights?
- A.Three all-round red lights in a vertical line✓
- B.Three all-round blue lights in a vertical line
- C.Two all-round red lights in a vertical line
- D.A single all-round red light
Why: Rule 28 allows a power-driven vessel constrained by her draft to optionally exhibit three all-round red lights in a vertical line in addition to prescribed lights, indicating to other vessels that maneuvering ability is severely limited by available water depth.
Frequently asked questions
- What lights does a vessel constrained by draft show?
- A CBD vessel shows all the normal lights of a power-driven vessel underway (Rule 23) plus, optionally, three all-around red lights in a vertical line. The cylinder dayshape may be displayed by day. Both the lights and the dayshape are permissive — the vessel may show them but is not required to.
- Do the US Inland Rules have a constrained-by-draft category?
- No. Constrained by draft is a COLREGS-only status. Under US Inland Rules there is no equivalent light or dayshape requirement for vessels restricted by their draft. This is one of the most frequently tested COLREGS-vs-Inland distinctions on USCG exams.
- How do three vertical red lights differ from two red lights and from red/white/red?
- Three vertical red lights indicate a vessel constrained by draft (CBD) — COLREGS only, optional. Two vertical red lights indicate a vessel not under command (NUC). Red over white over red (red/white/red) indicates a vessel restricted in ability to maneuver (RAM). Count the lights and note the color of the middle one: white middle = RAM, no middle white = NUC, three red = CBD.
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