Watchkeeper — know a vessel by her lights
Every picture in it is computed from the Collision Regulations. Nothing is drawn by hand.
What it is
Watchkeeper teaches the part of the Collision Regulations you have to know in the dark: what a vessel is showing, what it means, and what you must do about it.
It was built for people sitting an examination — Yachtmaster, Officer of the Watch, a national certificate — and for anyone who keeps a night watch and would rather recognise a vessel before reading her name.
Why it looks different from the others
Most apps in this corner of the App Store show you drawings: one picture per vessel, seen from one angle, made by hand once and never questioned again.
Watchkeeper has no drawings of lights in it at all. Every vessel is stored as her lights — each with the arc of visibility Rule 21 gives it, the bearing it is centred on, the height it is carried at and the range Rule 22 assigns it — and the picture is worked out from that, live, for whatever bearing and distance you ask for.
That is not a detail of implementation. It is the difference between memorising seven pictures and understanding why a vessel of 50 m or more shows two masthead lights head-on and a single sternlight from right astern. Turn the bearing and the lights come and go exactly where the Rules say they must, because there is nowhere else for them to come and go.
What is in it
Fifty vessels. Power-driven, towing and pushing, sailing and under oars, fishing, restricted in her ability to manoeuvre, not under command, constrained by draft, pilot vessels, aground and at anchor — with the balls, diamonds, cones, cylinder and rigid flag A they show by day.
Twenty-four encounters from Part B, each one a geometry rather than a diagram: your vessel, her bearing, her course, and what you would see of her at night. Overtaking, head-on, crossing, sailing tacks, the order of precedence in Rule 18, narrow channels, traffic separation schemes, restricted visibility.
The full text of Rules 1 to 37 — 615 paragraphs — searchable, with the International and the United States Inland wordings side by side. Every card links to the rule it comes from.
Sound signals for Rules 32 to 37, synthesised from the Rules rather than recorded: a short blast of about a second, a prolonged one of four to six, a whistle pitched by the length of the vessel as Annex III requires. Bells and gongs too.
The 26 single-letter signals of the International Code, and 16 IALA marks with their topmarks, colours and light rhythms, in Region A or Region B.
And a drill of 257 questions in eleven kinds, built from the same data. The wrong answers are the vessels genuinely confused with one another. The app will not ask a question whose answer cannot be told from what is on show — that is checked by tests across the whole catalogue. Spaced repetition brings each question back just before you would have forgotten it.
Where the facts come from
The text of the Rules is taken from the Navigation Rules and Regulations Handbook of the U.S. Coast Guard — a work of the United States Government, in the public domain — and cross-checked against 33 CFR on eCFR. Flag meanings are read from Pub. 102. The buoyage comes from 33 CFR part 62 and U.S. Chart No. 1.
Publications of the International Maritime Organization are not used, and no illustration from any other publication appears in the app. Every explanation and mnemonic was written for it.
What it costs
The app is free to download, and a good deal of it is free for good: the whole text of Rules 1 to 37, the sound signals, the flags, the buoyage, five vessels, three encounters, and forty questions of the drill.
One payment of $3.99 — never a subscription — opens the other forty-five vessels, the other twenty-one encounters, and the drill without a limit. The Rules themselves stay free whether you buy it or not.
What it is not
It is a study aid. It does not replace the official publication of the Collision Regulations that a vessel is required to carry, and it is not a navigational aid. The mariner remains responsible for consulting the current edition of the Rules and any local requirements.
It has no server behind it, no account, no analytics and no advertising. Everything except the purchase itself works with no signal at all, and your progress stays on your iPhone.
Requirements
iPhone running iOS 18.0 or later. English and Russian, switched inside the app rather than following the phone. The text of the Rules is in English in both, quoted word for word from the source.
Links
Support: https://watchkeeper.pages.dev/support
Privacy policy: https://watchkeeper.pages.dev/privacy
Contact: danielbiruk@icloud.com