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Part CIntermediate
Rule 28: Vessel constrained by draught
A CBD vessel may display optional special signals to show severe draught constraints.
Detailed Explanation
A vessel constrained by draught may, in addition to Rule 23 power-driven lights, show where best seen either three all-round red lights in a vertical line or a cylinder by day. These signals warn others that course deviation is severely limited.
Key Points
- CBD optional: 3 red all-round vertical + cylinder shape
- Still must carry normal power-driven underway lights
- Anti-collision duties still apply to CBD vessels
Examples
- A deep-draught VLCC transiting a shallow strait shows three all-round red lights in a vertical line in addition to her normal power-driven vessel lights, signalling CBD status per Rule 28.
- By day you see a cylinder shape on a large container vessel in a constrained waterway. Per Rule 28, this is the daymark for a vessel constrained by her draught — you avoid impeding her passage.
Common Mistakes
- Treating CBD signals as giving the same keep-clear priority as NUC or RAM instead of only an 'avoid impeding' obligation on other vessels.
- Displaying CBD lights in open ocean with ample depth under keel where the draught-depth relationship does not actually constrain the vessel.
- Forgetting that CBD signals are in addition to standard power-driven vessel lights, not a replacement.