Rule 27(e)
Too small for the full signal? A simplified version
Official rule text as published in the U.S. Coast Guard Navigation Rules
Source: USCG NavCen / eCFR Navigation Rules · Last updated September 13, 2026
(e) Whenever the size of a vessel engaged in diving operations makes it impracticable to exhibit all lights and shapes prescribed in (d), the following shall be exhibited: (i) three all-round lights in a vertical line where they can best be seen — the highest and lowest of these lights shall be red and the middle light shall be white; (ii) a rigid replica of the International Code flag “A” not less than 1 meter in height, with measures taken to ensure its all-round visibility.
MyCOLREGS explanation
Whenever a vessel engaged in diving operations is too small to exhibit the full Rule 27(d) signal, she shall exhibit: three all-round lights in a vertical line, red-white-red, and a rigid replica of the International Code flag "A" not less than 1 meter in height. The red-and-white diagonal "diver down" flag shown alongside it is the flag most U.S. recreational boaters actually recognize on the water - it is not the official Navigation Rules signal (the "A" flag is), but it is commonly flown in addition to it.
Summary
A small dive boat often cannot practically carry the full dredging/underwater-operations signal from Rule 27(d) - masthead light, sidelights, sternlight, obstruction-side reds and greens, all of it. Rule 27(e) gives her a simplified fallback instead: the same red-white-red three-light column used by any restricted vessel, plus a rigid, all-round-visible replica of the International Code flag 'A' - a two-colored (blue-and-white) swallow-tailed flag - at least 1 meter tall.
Real World Example
The rigid 'A' flag is what most recreational boaters actually encounter near a dive site, since small dive boats rarely carry the full Rule 27(d) light array. Seeing it means divers are in the water nearby - slow down and keep well clear, the same way you would for any restricted-ability vessel.
Practice Questions
Q1. A small boat displays a rigid replica of the International Code flag 'A', illuminated so it's visible even after dark, along with a red-white-red light column. Under Rule 27(e), what does this simplified signal tell you?
A. She is a pilot vessel on duty.
B. She is too small to carry the full Rule 27(d) diving-operations signal, and is engaged in diving operations.
C. She is not under command.
D. She is fishing.
Q2. Under Rule 27(e), what two things together make up the simplified diving-operations signal for a vessel too small to carry the full Rule 27(d) array?
A. Two all-round red lights, and a ball shape.
B. A masthead light, and sidelights.
C. Three all-round lights in a vertical line (red-white-red), and a rigid replica of the International Code flag "A" at least 1 meter tall.
D. A single all-round white light, and a diamond shape.
Practice Question Answers
Q1.
B. She is too small to carry the full Rule 27(d) diving-operations signal, and is engaged in diving operations. Rule 27(e) is a size-based fallback specifically for diving operations: when the full Rule 27(d) light array is impracticable to carry, a small vessel shows the red-white-red column plus a rigid 'A' flag instead. A, C, and D each have their own distinct, unrelated signals.
Q2.
C. Three all-round lights in a vertical line (red-white-red), and a rigid replica of the International Code flag "A" at least 1 meter tall. Rule 27(e)(i) and (ii) together: the red-white-red three-light column, plus the rigid 'A' flag with all-round visibility. A, B, and D each describe signals used for other situations covered elsewhere in the Rules.