COLREGs: vessel give-way rules with case studies

The logic of COLREGs

COLREGs (the Convention on the International Regulations for Preventing Collisions at Sea, 1972) is 38 rules that apply identically across all seas and oceans. The core idea: every vessel must avoid collision regardless of formal “right”. Rule 2(a) says explicitly: nothing in these rules exempts from the consequences of neglecting ordinary practice of seamen.

ISSA/RYA exams most often ask about rules 9, 10, 12–18, lights (20–31) and sound signals (32–36). Below — a breakdown with typical scenarios.

Rule 9 — navigation in narrow channels

In a narrow channel or fairway a vessel shall keep as near to its starboard side as is safe and practicable. Key consequences:

• A vessel less than 20 m long or a sailing vessel shall NOT impede a vessel that can safely navigate only within a narrow channel.
• Crossing a narrow channel is prohibited if it impedes a vessel restricted to it.
• Overtaking in a narrow channel: the overtaker sounds a signal (two prolonged + one short to overtake on the overtaken vessel’s starboard side, two prolonged + two short on the port side); the overtaken vessel responds prolonged-short-prolonged-short (agreement) or five short blasts (doubt/disagreement).

Typical situation. You are on a 9-metre yacht heading down a narrow channel toward a containership. Solution: stay close to the starboard side, give up the fairway entirely if necessary, sound the manoeuvring signals.

Rule 10 — Traffic Separation Schemes (TSS)

TSS — corridors marked on the chart with magenta lines that separate opposing traffic flows. Rules for a yacht:

• Travel in the appropriate lane in the general direction of traffic.
• Avoid crossing lanes; if you must, cross at as close to 90° to the flow as possible (not at a slant).
• A sailing vessel and a vessel under 20 m shall not impede vessels using the lane.
• Where possible use inshore traffic zones — with the same constraints.

Rule 12 — between sailing vessels

An examiners’ favourite, because there are three cases:

1. Different tacks. A vessel on the port tack gives way to one on the starboard tack. The tack is determined by the side the wind hits the sail: wind on the port side — port tack.
2. Same tack. The windward vessel gives way to the leeward one. Windward — the side from which the wind comes relative to the other vessel.
3. Doubt. If a vessel on the port tack sees another to windward and cannot tell its tack — assume she must give way.

Typical situation. Two yachts on opposite courses on a beam reach: one with wind from the right, the other from the left. The one with wind from the left (port tack) gives way.

Rules 13–15 — power-driven vessels

Rule 13 — overtaking. The overtaker (approaching from more than 22.5° abaft the other vessel’s beam) always gives way, regardless of vessel type. Once you start overtaking, you remain the overtaker until fully past and clear.

Rule 14 — head-on. Two power-driven vessels meeting on reciprocal or nearly reciprocal courses must both alter to starboard so as to pass on each other’s port side. Sign of the situation: at night you see both sidelights of the other vessel and her masthead lights in line.

Rule 15 — crossing. The power-driven vessel which has the other on her starboard side gives way. Simple rule: “starboard sees, starboard gives”.

Rules 16–17 — who acts how

Rule 16. The give-way vessel shall act early and substantially so the give-way is clearly visible. Don’t weave — change course significantly (at least 30–45°).

Rule 17. The vessel required to keep her course and speed (stand-on vessel) must do so until it becomes obvious that the give-way vessel is not taking action. The stand-on must then manoeuvre — but avoid altering to port if the other vessel is on her port side.

Rule 18 — hierarchy of responsibility

“Who gives way to whom” in complex situations. Order of seniority (above gives way to below):

1. Power-driven vessel.
2. Sailing vessel.
3. Vessel engaged in fishing (with trawls or nets restricting manoeuvrability).
4. Vessel restricted in her ability to manoeuvre (e.g. cable-layer, dredger).
5. Vessel not under command (NUC).

Simple mnemonic: NUC → RAM → Fishing → Sailing → Power. A sailing yacht gives way to a fishing trawler, but any power-driven vessel (other than the listed categories) must give way to a sailing one.

Exception: in a narrow channel or TSS, a sailing vessel must not impede the passage of large vessels (see rules 9 and 10).