COLREGs – Shapes

15 January 2026 5 min read Bridge, Latest Articles, Navigation, Watchkeeping

What vessels are telling you in daylight — and why daylight collisions still happen

Use the links below to jump to any section:

Why Shapes Still Matter in Modern Navigation
When Shapes Must Be Displayed
The Core Shapes Every OOW Must Recognise Instantly
Power-Driven Vessels and the Absence of Shapes
Vessels Not Under Command
Vessels Restricted in Their Ability to Manoeuvre
Vessels Constrained by Their Draught
Fishing Vessels
Towing and Pushing Operations
Sailing Vessels and Special Cases
Anchored and Aground Vessels
Dredging, Underwater, and Obstruction Operations
Small Craft, Non-Compliance, and Missing Shapes
Common Misidentifications and Daylight Traps
Using Shapes with Radar, AIS, and Visual Bearings
What to Do When Shapes Are Missing or Conflicting

1. Why Shapes Still Matter in Modern Navigation

A persistent myth on modern bridges is:

“Shapes are obsolete — we have AIS and radar.”

This belief has contributed directly to daylight collisions.

Shapes exist because:

daylight removes the contrast advantage of lights
radar does not show operational constraints
AIS can be wrong, delayed, or misleading

Shapes answer a question electronics often cannot:

“How free is this vessel to manoeuvre?”

Ignoring shapes means ignoring intent and limitation.

2. When Shapes Must Be Displayed

Shapes must be displayed:

from sunrise to sunset
when required by the vessel’s condition
regardless of visibility quality

They must be:

clearly visible
properly rigged
correctly positioned

If a vessel is required to display shapes and does not, that vessel is non-compliant — but your responsibility to avoid collision remains.

3. The Core Shapes Every OOW Must Recognise Instantly

Every OOW must instantly recognise:

ball
diamond
cone (apex up or down)

Recognition must be immediate, not analytical.

If you are stopping to “work it out,” you are already late.

4. Power-Driven Vessels and the Absence of Shapes

Most power-driven vessels underway display no shapes.

This absence itself is information.

It tells you:

the vessel considers itself fully manoeuvrable
normal crossing, overtaking, and head-on rules apply

Do not assume absence of shapes equals absence of risk.

It simply means no declared restriction.

5. Vessels Not Under Command

A vessel not under command displays two black balls in a vertical line.

This is one of the most critical shapes.

Operational meaning:

the vessel cannot manoeuvre
it may drift unpredictably
engine, steering, or propulsion failure is likely

If you see NUC shapes, your priority is early, wide clearance.

Do not attempt to negotiate close passing.

6. Vessels Restricted in Their Ability to Manoeuvre

These vessels display ball–diamond–ball vertically.

This shape combination means:

the vessel is constrained by its work
it cannot comply with COLREGs normally
you must keep clear

Typical operations include:

dredging
cable laying
underwater operations
buoy maintenance

Ignoring RAM shapes is a classic daylight accident precursor.

7. Vessels Constrained by Their Draught

A vessel constrained by draught may display a black cylinder.

This is a statement of limitation, not priority.

It means:

the vessel’s available manoeuvring options are severely limited
deviation from course may be unsafe

In narrow channels, this shape demands early and decisive avoidance, not last-minute compliance debates.

8. Fishing Vessels

Fishing vessels display:

two cones apex together (hourglass shape)

Operational reality:

fishing gear may extend far from the vessel
the vessel may turn unpredictably
gear may not be visible

Fishing shapes indicate hidden risk, not just vessel type.

9. Towing and Pushing Operations

Towing vessels may display a diamond shape when the tow exceeds certain lengths.

This warns that:

the tow may trail far astern
the tug’s manoeuvrability is limited
passing close astern may foul the tow

Shapes here warn you about what radar might not show.

10. Sailing Vessels and Special Cases

Sailing vessels normally display no shapes.

When using engines, they should display a cone apex down, indicating power-driven status.

Operational trap:

Many sailing vessels motor-sail without displaying the cone.

Do not assume compliance.

Treat sailing vessels with caution and margin.

11. Anchored and Aground Vessels

Anchored vessels display one black ball.

Aground vessels display three black balls in a vertical line.

Daylight groundings are often underestimated because:

the vessel appears stationary
radar vectors show no movement
officers assume clearance exists

Shapes tell you why the vessel is stationary.

12. Dredging, Underwater, and Obstruction Operations

Some RAM vessels display additional shapes indicating:

safe side to pass
obstructed side

These shapes are critical during daylight operations near ports, channels, and offshore works.

Ignoring these indicators leads to contact accidents, not just collisions.

13. Small Craft, Non-Compliance, and Missing Shapes

In reality:

many small craft do not display shapes
some vessels display incorrect shapes
rigging may be poor or obscured

This does not invalidate the system.

It means professional ships must compensate.

Expect non-compliance — never rely on perfection.

14. Common Misidentifications and Daylight Traps

Recurring errors include:

assuming no shapes means no constraint
mistaking RAM vessels for fishing vessels
ignoring cylinders in narrow channels
trusting AIS status over visual shapes
failing to notice shapes against cluttered backgrounds

Daylight reduces contrast — shape awareness must increase.

15. Using Shapes with Radar, AIS, and Visual Bearings

Shapes provide context.

Radar provides movement.

AIS provides declared status.

When these disagree:

trust physical reality first
increase CPA
reduce speed if necessary
call the Master early

Visual evidence beats digital claims.

16. What to Do When Shapes Are Missing or Conflicting

When shapes are unclear or contradictory:

assume reduced manoeuvrability
avoid close-quarters situations
take early and obvious action
communicate if appropriate
document concerns in the log

Uncertainty is not neutral — it is risk.