Yachtmaster theory guides
Offshore Theory, written by a superyacht bosun with a commercial Yachtmaster Offshore · 30 October 2026
Free guides to the Yachtmaster Offshore theory, each one a method worked through with numbers you can check: tides, chartwork, the course to steer, passage planning, lights, buoyage and the forecast. Each links to the lessons of the course and to the free reading notes.
The exam
- Yachtmaster Offshore theory exam: what's in it and how to passWhat the RYA says the theory covers, subject by subject, and a study plan.
- Yachtmaster Offshore in 2027: requirements, theory and how to prepareWhat the RYA asks for, and a month-by-month plan from this winter to a practical exam in the 2027 season.
- Yachtmaster Coastal vs Offshore theorySame theory, different practical: the requirements side by side, and online vs classroom.
- Yachtmaster questions and answersPractice questions with the answer explained, each linked to its lesson or notes.
Tides
- Secondary port tidal heights, step by stepTimes and heights at a secondary port from the standard port and its differences, with a worked example.
- Springs or neaps: interpolating the tidal curveWhich curve to read on the day, and how to go part of the way between springs and neaps.
- The rule of twelfths, and when it failsThe 1, 2, 3, 3, 2, 1 shortcut worked through, and the ports and days where it gives the wrong answer.
- Clearance under the keel and drying heightsSounding plus height of tide minus draught, drying heights, and the tide you need to cross a bar.
- Tidal diamonds and the tidal stream atlasSet and rate for the hour from a diamond or the atlas, and interpolating between springs and neaps.
Chartwork and position fixing
- True, magnetic and compass: variation and deviationUpdating variation, reading the deviation card and converting both ways without getting the sign wrong.
- The cocked hat and crossing bearingsChoosing marks, the angle of cut, the order you take them in, and what the cocked hat tells you.
- The running fixOne mark, two bearings and the run between them: how to transfer the line, with and without a stream.
- Dead reckoning vs estimated positionWhat a DR leaves out, what an EP adds, and how each is marked and trusted on the chart.
- Set, drift and the estimated positionFrom the dead reckoning to the EP: the stream for the time run, leeway, and the triangle drawn the right way.
- Course to steer and the tidal triangleThe one-hour vector triangle drawn step by step, with leeway, and down to a compass course.
Passage planning and weather
- Planning a passage, step by stepFrom the question of whether to go, through the tide at each end and the stream, to the plan on one page.
- The shipping forecast and the barometer: go or no-goReading the shipping forecast, the barometric tendency and the sky, and turning them into a decision.
Lights and buoyage
- Navigation lights and shapes: a quick referenceEvery vessel's lights and day shapes in one place, with their arcs and what they tell you.
- IALA buoyage region A, by day and by nightLateral, cardinal, isolated danger, safe water, special and emergency wreck marks: shapes, colours and lights.