Rules of the Road — COLREGS

The Basic Principle

Every vessel must use all available means to determine the risk of collision and must take action in ample time. Action must be large enough to be readily apparent to the other vessel, taken early, and must result in passing at a safe distance. Half-hearted, late, or small alterations are worse than useless — they cause confusion.

Golden rule: If you're unsure whether there is a risk of collision, assume there is one.

Priority Order — Who Gives Way to Whom

The vessel lowest on this list must give way to all above it:

1

Vessel Not Under Command (NUC) — has right of way over all

2

Vessel Restricted in Ability to Manoeuvre (RAM) — dredgers, minesweepers, laying cable

3

Vessel Constrained by Draft — in narrow channel with no room to deviate

4

Vessel Engaged in Fishing — trawls, nets deployed (NOT trolling or rod fishing)

5

Sailing Vessel under sail alone

6

Power-driven vessel — motor vessels, sailing boats with engine running

Important: A sailing vessel using its engine is classified as a power-driven vessel for COLREGS purposes, regardless of whether sails are hoisted.

Stand-on vs Give-way Vessels

In any encounter, one vessel is the give-way vessel (must take avoiding action) and the other is the stand-on vessel (must maintain course and speed).

The give-way vessel shall take early and substantial action to keep well clear.
The stand-on vessel shall maintain course and speed — but must be ready to take action if a collision becomes inevitable. The stand-on vessel may take action once it becomes clear the give-way vessel is not acting appropriately.
Do not alter course to port for a vessel on your port side (in a crossing situation).
Do not alter course towards the vessel you are giving way to.

The Overtaking Rule

Any vessel overtaking any other vessel must keep clear — regardless of whether either is sail or power. You are overtaking if you approach from a direction more than 22.5° abaft the other vessel's beam (i.e. from the stern sector). When in doubt, assume you are overtaking.

The overtaking obligation persists until you are finally past and clear — you cannot suddenly claim crossing or head-on rules once you have committed to an overtaking pass.

Head-on Situations

When two power-driven vessels meet head-on or nearly head-on, both must alter course to starboard so as to pass port-to-port.

A head-on situation exists when you see both sidelights of the approaching vessel and/or its masthead light(s) are in line. If there is any doubt whether it is head-on or crossing — treat it as head-on and alter to starboard.

Crossing Situations

When two power-driven vessels are crossing so as to involve risk of collision:

The vessel which has the other on her starboard side is the give-way vessel.
She must avoid crossing ahead of the stand-on vessel — if necessary stop, reverse, or pass astern.
The stand-on vessel (with the other on her port) maintains course and speed.

Mnemonic

"If to starboard red appear, 'tis your duty to keep clear."

If you can see a red light (port side of the other vessel), they are on your starboard side — you give way.

Navigation Light Patterns

Required between sunset and sunrise, and in restricted visibility at all times.

Vessel Type	Lights Shown	Notes
Sailing vessel under sail	Red (port), Green (starboard), White (stern)	Combined tri-colour lantern acceptable under 20m. No white steaming light.
Power-driven vessel underway	White masthead light(s), Red (port), Green (starboard), White (stern)	Vessels ≥50m carry two masthead lights; forward lower, aft higher.
Sailing vessel using engine	Same as power-driven vessel — add steaming light	Also display cone point-down by day.
Vessel at anchor	All-round white light (fore); vessels ≥50m add all-round white aft (lower)	Displayed from highest practicable point. Black ball by day.
Vessel aground	Anchor lights PLUS two all-round red lights (vertical)	Three black balls in vertical line by day.
Vessel not under command (NUC)	Two all-round red lights (vertical)	Two black balls by day.
Vessel restricted in ability to manoeuvre (RAM)	Red–White–Red all-round lights (vertical)	Ball–Diamond–Ball by day.
Vessel engaged in fishing (trawling)	Green over white all-round (vertical); sidelights and stern if making way	Two cones apex-to-apex by day.
Vessel engaged in fishing (not trawling)	Red over white all-round (vertical); white light in direction of gear if gear extends >150m	Two cones apex-to-apex by day.
Pilot vessel on duty	White over red all-round (vertical)	Sidelights and stern if underway.

Sound Signals

In restricted visibility (fog, rain, mist) — signals must be made at intervals not exceeding 2 minutes:

Vessel	Signal	Interval
Power vessel underway and making way	1 prolonged blast	Every 2 min
Power vessel underway but stopped (no way)	2 prolonged blasts (with 2 sec gap between)	Every 2 min
Sailing vessel underway	1 prolonged + 2 short blasts	Every 2 min
Vessel at anchor	Rapid ringing of bell for 5 seconds	Every 1 min
Vessel aground	3 distinct strokes on bell + rapid bell + 3 distinct strokes	Every 1 min
NUC, RAM, fishing, towing/being towed, constrained by draft	1 prolonged + 2 short blasts	Every 2 min

Manoeuvring signals (in sight of each other):

1 short blast — I am altering course to starboard
2 short blasts — I am altering course to port
3 short blasts — I am operating astern propulsion
5 or more short blasts — I do not understand your intentions / doubt you are taking sufficient action

Narrow Channels

Keep to the starboard side of the channel.
Vessels under 20m and sailing vessels must not impede vessels that can only navigate safely within the channel.
Do not anchor in a narrow channel except in an emergency.
Overtaking in a narrow channel requires agreement — the vessel ahead signals if safe to pass.
A vessel leaving a berth or anchorage into a narrow channel must give way to vessels in the channel.

Traffic Separation Schemes (TSS)

When crossing a TSS, do so at right angles (90°) to the traffic flow.
Do not impede vessels following the traffic lane.
Vessels under 20m and sailing vessels must not impede power-driven vessels following the lane.
Avoid anchoring in separation zones if possible.
Enter and leave lanes at the ends, or join from the sides at a shallow angle.

Restricted Visibility

Proceed at safe speed adapted to conditions — ready to stop within half the distance of visibility.
Have radar and AIS operational. Plot all targets.
Make all required sound signals.
If you hear only another vessel's fog signal and cannot determine position, reduce to bare steerageway or stop.
Avoid taking action to port for a vessel forward of the beam (except overtaking).
The radar-plotted CPA (Closest Point of Approach) should be the main guide to action — not assumptions.

In fog in the Mediterranean: You will encounter ferries and commercial vessels moving at 20+ knots with very short notice. In a TSS or ferry route, consider anchoring or waiting for visibility to improve.

Rule of Thumb Mnemonics

Key Mnemonics

"If to starboard red appear, 'tis your duty to keep clear."
→ Red light = their port side = they are on YOUR starboard = you give way.

"Green to green, red to red — perfect safety, go ahead."
→ Both see matching sidelights = head-on, alter to starboard and pass port-to-port.

"When all three lights you see ahead — port your helm and show your red."
→ Seeing both sidelights plus masthead = head-on. Turn to starboard (show them your red/port).

"Big ships in small channels — stay out of their way."
→ Vessels constrained by draft outrank you regardless of sail/power status.

🧭 Rules of the Road — COLREGS