COLREGS Day Shapes: Every Shape and What It Means
At night you read a vessel by her lights. By day you read her by her shapes: black balls, cones, diamonds and cylinders hoisted where you can see them. There are only four basic shapes, so once you know the handful of combinations, day shape questions become some of the easiest points on the Rules of the Road exam.
Everything below is checked against the 2022 U.S. Coast Guard Navigation Center (NAVCEN) Navigation Rules handbook, International and Inland.
The quick answer
One ball means anchored. Three balls mean aground. Two balls mean not under command. Ball, diamond, ball means restricted in ability to maneuver. Two cones point to point mean fishing. A cone point down means a sailboat under power. A diamond means a long tow. A cylinder means constrained by draft, International only.
The four shapes and their sizes
Rule 20(d) says the rules about shapes "shall be complied with by day." Annex I sets the sizes. Shapes are black, and:
- Ball: a diameter of not less than 0.6 meter.
- Cone: a base diameter of not less than 0.6 meter and a height equal to its diameter.
- Diamond: two of those cones with a common base.
- Cylinder: a diameter of at least 0.6 meter and a height of twice its diameter. This one is only in the International annex, since the Inland Rules have no shape that uses it.
Shapes in a vertical line are at least 1.5 meters apart. A vessel under 20 meters may use smaller shapes "commensurate with the size of the vessel" and space them closer.
Every day shape at a glance
| Shape | Meaning | Rule |
|---|---|---|
| One ball (forward) | At anchor | Rule 30(a)(ii) |
| Three balls in a vertical line | Aground | Rule 30(d)(ii) |
| Two balls in a vertical line | Not under command | Rule 27(a)(ii) |
| Ball, diamond, ball in a vertical line | Restricted in ability to maneuver | Rule 27(b)(ii) |
| Two balls on one side, two diamonds on the other | Dredging or underwater operations with an obstruction (balls mark the obstructed side, diamonds the side to pass) | Rule 27(d) |
| Rigid replica of Code flag "A", at least 1 meter high | Small vessel diving, when the full shapes aren't practicable | Rule 27(e)(ii) |
| Three balls: one at the foremast head, one at each end of the fore yard | Engaged in mineclearance | Rule 27(f) |
| Two cones, apexes together | Engaged in fishing (trawling or otherwise) | Rule 26(b), 26(c) |
| One cone, apex up, toward the gear | Fishing with outlying gear more than 150 meters horizontally from the vessel | Rule 26(c)(ii) |
| One cone, apex down (forward) | Sailing vessel also under power | Rule 25(e) |
| One diamond | Towing vessel and tow, when the tow is longer than 200 meters; also partly submerged objects being towed | Rule 24 |
| One cylinder | Constrained by her draft (International only) | Rule 28 |
Memory hooks
- Balls are about being stuck. One ball, anchored. Two balls, not under command. Three balls, aground. The more balls, the worse the day.
- A diamond in the middle means "I'm working." Ball, diamond, ball is the restricted in ability to maneuver signal, and it matches the red, white, red lights for the same vessel at night.
- Cones point at the story. Two cones point to point look like an hourglass, which is fishing. One cone pointing up shows which way the fishing gear runs. One cone pointing down says the sails are up but the engine is on.
- Diamonds are the safe side. On a dredge, pass on the side with the two diamonds, never the side with the two balls.
Inland differences to know
- No cylinder inland. Rule 28, constrained by her draft, is International only.
- Small sailboats motoring. Under Inland Rule 25(e), a vessel under 12 meters isn't required to show the cone, apex down, but may.
- Special anchorage areas. Under Inland Rule 30(g), a vessel under 20 meters at anchor in a special anchorage area designated by the Coast Guard doesn't have to show the anchor lights and shapes.
Small vessel exemptions (both rule sets)
- Rule 27(g): vessels under 12 meters, except when diving, don't have to show the Rule 27 lights and shapes.
- Rule 30(e): a vessel under 7 meters at anchor, away from channels, fairways, anchorages and normal traffic, doesn't have to show the anchor ball.
- Rule 30(f): a vessel under 12 meters aground doesn't have to show the three balls.
Exam practice questions
These come straight from the USCG question bank used in COLREGS Prep.
Practice question 1. BOTH INTERNATIONAL & INLAND What day-shape is to be shown by a vessel aground?
- A cylinder
- Two cones with their apexes together
- Two black balls in a vertical line
- Three black balls in a vertical line
Show answer
D. Three black balls in a vertical line
Practice question 2. BOTH INTERNATIONAL & INLAND In the daytime, you see a large sailing vessel on the beam. You know that she is also propelled by machinery if she shows __________.
- a basket
- a black ball
- a black cone
- two black cones
Show answer
C. a black cone
Practice question 3. BOTH INTERNATIONAL & INLAND You are approaching a vessel dredging during the day and see two balls in a vertical line on the port side of the dredge. These shapes mean that __________.
- you should pass on the port side of the dredge
- there is an obstruction on the port side of the dredge
- the dredge is not under command
- the dredge is moored
Show answer
B. there is an obstruction on the port side of the dredge
Practice question 4. BOTH INTERNATIONAL & INLAND During the day, a vessel with a tow over 200 meters in length will show __________.
- a black ball
- a diamond shape
- two cones, apexes together
- one cone, apex upward
Show answer
B. a diamond shape
Studying for a captain's license? Practice every lights and shapes question in the USCG bank, with diagrams and missed-question review, in COLREGS: Rules of the Road for iPhone and iPad. Download on the App Store
Frequently asked questions
What are day shapes in COLREGS?
Day shapes are black balls, cones, diamonds and cylinders that vessels hoist by day to show their status, such as anchored, aground, fishing, towing, not under command, or restricted in their ability to maneuver. Rule 20(d) says the shapes apply by day, and Annex I sets their sizes.
What does one black ball mean on a boat?
One black ball shown in the forepart of the vessel means she is at anchor, under Rule 30(a)(ii).
What do three black balls in a vertical line mean?
Three balls in a vertical line mean a vessel aground, under Rule 30(d)(ii). A vessel engaged in mineclearance also shows three balls, but one at the foremast head and one at each end of the fore yard, not in a vertical line.
What does a cone with the point down mean?
A cone, apex downwards, shown forward means a sailing vessel that is also being propelled by machinery, under Rule 25(e). Under the Inland Rules, a vessel under 12 meters doesn't have to show it but may.
What does a black cylinder mean?
A cylinder is the International day shape for a vessel constrained by her draft, under Rule 28. The U.S. Inland Rules have no constrained-by-draft signal.