COLREG Collision Avoidance – Interactive Guide for Skippers
Collision avoidance is not a collection of isolated right-of-way slogans. A skipper must maintain a proper lookout, proceed at a safe speed, recognize developing risk, identify the encounter, understand vessel status, take early and substantial action where required, and continue monitoring until the vessels are finally past and clear.
The collision-avoidance chain
1. Detect
Maintain lookout by sight, hearing and all appropriate available means.
2. Assess
Determine whether risk of collision exists. If in doubt, treat the risk seriously.
3. Classify
Head-on, crossing, overtaking, restricted visibility, or a special vessel-status situation?
4. Act & verify
Make an appropriate manoeuvre and monitor its effect until finally past and clear.
Interactive encounter simulator
Set both vessels' course and speed. The simulator projects their motion and calculates a simplified CPA/TCPA from constant-course, constant-speed vectors.
Head-on, crossing or overtaking?
Classify the encounter before thinking about manoeuvres. In real situations, classification depends on the COLREG definitions and the observed geometry—not on a single screenshot.
Crossing situation trainer
For two power-driven vessels crossing so as to involve risk of collision, the vessel that has the other on her own starboard side keeps out of the way. Use the trainer to practise recognition.
Overtaking recognition trainer
Overtaking is not simply “I am faster.” The rule uses the relative approach from more than 22.5° abaft the beam. The overtaking vessel keeps out of the way until finally past and clear.
Constant bearing, decreasing range
A classic warning sign is a target that remains at approximately the same relative bearing while the range closes. Use repeated observations rather than trusting a single visual impression.
Action simulator: course alteration and CPA
Start from a collision-risk geometry, then alter your course and see how the simplified predicted CPA changes. This teaches why an alteration should be large enough to be readily apparent and why its result must be checked.
Stand-on vessel: it does not mean “do nothing forever”
Initial duty
In the applicable crossing framework, the stand-on vessel generally keeps course and speed.
Developing failure
When it becomes apparent that the give-way vessel is not taking appropriate action, the stand-on vessel may take action as allowed by the Rules.
Collision cannot be avoided alone
When collision cannot be avoided by the give-way vessel's action alone, the stand-on vessel must take such action as will best aid avoidance.
Navigation-light encounter trainer
At night, identify aspect first. Then combine the light pattern with bearing and range trend.
Vessel status recognition
Ordinary power-vessel crossing rules are not the whole COLREG picture. Vessel status, activity and circumstances can change responsibilities. Click a status to review the recognition problem.
Safe-speed decision tool
There is no universal “safe speed in knots.” Safe speed depends on circumstances and conditions. Use this qualitative trainer to see how risk factors increase the need for time and sea room.
Restricted-visibility scenario
When vessels are not in sight of one another in or near restricted visibility, do not blindly apply the visual head-on/crossing shortcuts. Use the restricted-visibility rules and radar information appropriately.
Lookout workload trainer
Mark what is currently competing for the skipper's attention. The tool demonstrates how quickly a single-person watch can become overloaded.
Random COLREG skipper scenarios
COLREG rule map for collision avoidance
| Rule area | Practical skipper question | Core training idea |
|---|---|---|
| Rule 5 — Look-out | Am I actually detecting all relevant targets and information? | Use sight, hearing and all available means appropriate to the circumstances. |
| Rule 6 — Safe speed | Can I stop or manoeuvre effectively with the information and sea room available? | Speed must suit visibility, traffic, manoeuvrability and conditions. |
| Rule 7 — Risk of collision | Is the target's relative bearing changing enough, and what is range doing? | Use all available means; if in doubt, risk should be deemed to exist. |
| Rule 8 — Action | Will my action be obvious, timely and effective? | Positive, made in ample time, with due regard to good seamanship. |
| Rule 13 — Overtaking | Am I approaching from the overtaking sector? | Overtaking vessel keeps out of the way until finally past and clear. |
| Rule 14 — Head-on | Are two power-driven vessels meeting on reciprocal or nearly reciprocal courses? | Each alters course to starboard so they pass port-to-port. |
| Rule 15 — Crossing | Do I have the other power-driven vessel on my starboard side? | If risk exists, that vessel is the give-way vessel in the ordinary crossing case. |
| Rule 16 — Give-way | Am I taking early and substantial action? | Keep well clear. |
| Rule 17 — Stand-on | Is the give-way vessel acting appropriately? | Keep monitoring; stand-on duties evolve if avoidance action fails. |
| Rule 18 — Responsibilities | What is the other vessel's status and activity? | Do not apply a simplistic power-vs-power crossing rule to every target. |
| Rule 19 — Restricted visibility | Are vessels not in sight of one another in restricted visibility? | Use the specific restricted-visibility framework. |
Pre-encounter skipper checklist
Final collision-avoidance quiz
Continue your navigation training
Combine collision avoidance with Sailing at Night, How to Read a Nautical Chart, Marine VHF Radio Basics and your passage-planning workflow. The goal is not to memorize isolated rules—it is to build a reliable traffic picture early enough to avoid creating a close-quarters situation.
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