International Regulations for Preventing Collisions at Sea
A reference and revision tool for deck officers. 41 light configurations viewable from any aspect, the full text searchable and read aloud, and a scored examination. Works entirely offline.
A book requires you to know where to look before you open it. Here you begin from the arrangement — red over white over red, two red lights in a vertical line — and arrive at the vessel, the obligation and the rule it comes from.
Always free
Twenty-one encounters, set out in full
Crossing, head-on, overtaking, narrow channel, traffic separation schemes, restricted visibility — each labelled stand-on, give-way or caution, with the governing rule.
Identification by lights and shapes
Describe an arrangement in plain words and work down to the vessel it belongs to.
Built for watchkeepers
Every light, with its arc.
Each configuration lists the lights actually shown, their arc of visibility and the rule they come from — and can be turned to bow, stern, port or starboard, in lights or in day shapes.
Rules 23–31 + Annex II
Four viewing aspects
The same vessel as she appears from ahead, astern and from either beam. A printed diagram can only show one of them.
Lights and day shapes together
Switch between the night arrangement and the daytime shapes for the same vessel, without losing your place.
What is inside
Five ways to reach the same rule.
SITUATIONS
Start from the encounter
Describe the situation, or pick from twenty-one common ones, and read your obligation.
LIGHTS
Start from what you see
Forty-one configurations covering Rules 23 to 31 and Annex II, filterable by vessel type and activity.
RULES
Start from the text
The full regulation, searchable, with a glossary and saved rules for the ones you keep returning to.
AUDIO
Listen hands-free
The whole COLREG read aloud, rule by rule, with your position remembered.
QUIZ
Prove you know it
Practise by category or sit a scored twenty-question exam. Accuracy is tracked per category.
OFFLINE
No connection required
Rules, diagrams, questions and audio are stored on the device. A day and a night theme are both provided.
Written and checked by a serving Master Mariner. Every explanation, diagram and question is original work, verified against the regulation before it ships. Safety-critical content — distress signals, identification by lights and shapes — is free and stays free.
Day and night
One app, two watches.
Lights · nightQuizAudioDay shapes
Questions
Before you download
Does it work without internet?
Yes. Rules, diagrams, questions and audio are all stored on the device. It behaves the same mid-ocean as it does alongside.
Who is it for?
Deck officers and cadets preparing for OOW, Chief Mate and Master examinations, and anyone standing a navigational watch who wants the rules to become instinctive.
Which parts of the COLREGs are covered?
Steering and sailing rules, lights and shapes, sound and light signals, and distress signals — explained for watchkeepers rather than for lawyers.
What is it intended for?
Study, revision and examination preparation. It is a reference and a training aid, not an aid to navigation, and it does not replace the official text.
Advisory only. The official IMO COLREG 1972 text prevails. Rules 2, 5, 7 and 8 — good seamanship, look-out, risk assessment, action — apply at all times.
