Yachtmaster Ocean Theory Course

The RYA Yachtmaster Ocean Theory Course examines astro-navigation, the use of the sextant and worldwide meteorology. It assumes a knowledge of all the subjects covered in all the other shorebased courses. Courses are run in Southampton, London and on Zoom.

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For centuries sailors have guided their ships across the oceans by celestial navigation or nautical astronomy. On the RYA Yachtmaster Ocean Theory Course you will learn how to fix your position with a sextant by observing the sun, moon, stars and planets. For the modern sailor it is not only a fascinating art, but an essential alternative to electronic navigation when crossing oceans.

Looking to practice using a sextant? See our Celestial Sailing Weekends where you can get some hands on practice.

This course is for those aspiring to blue water cruising and is ideal for holders of the Yachtmaster Offshore certificate of competence who are preparing for their first ocean voyage. It is also suitable for those who enjoy and have a general interest and curiosity in navigation and how one can find a position by using a sextant and the heavenly bodies.

Minimum Pre Course Experience: Coastal and offshore sailing. Prior to the course your navigation skills should be at the standard of the Coastal Skipper / Yachtmaster Offshore shorebased course.

Ability after the Course: Background knowledge to skipper a yacht on ocean passages.

Course Content: Astro-navigation, ocean meterology.

We provide a comprehensive set of materials to assist you with the course including:

  • RYA questions and answers

For those wanting the full Yachtmaster Ocean certificate we can help arrange the 600-mile qualifying passage.

Some difficult principles to grasp! It takes a while to get to grips with the principles of astro navigation so do not be put off if you don't understand everything you will be taught straight away.

A knowledgeable instructor who will give you plenty of support if you need it.

It is not a problem if you have to miss a lesson providing you are prepared to put some effort into catching up. The sessions are recorded to watch later in the week There is a fair bit of homework each session and providing you do this you know you will have caught up sufficiently. Also the instructor is available on phone/email in between sessions.

Start/Finish Times

Courses are run over 40 hours plus time for exams. Evening classes generally start at 6.00pm with the instructor being available from 5.30pm. Weekend classes start at 9am. Week day classes are 9.30am to 5.30pm.

This is a course in astro-navigation and worldwide meteorology which also reveals the mysteries of the sextant. It assumes a knowledge of all subjects covered in the other shorebased courses.

The earth and the celestial sphere

The PZX triangle

The sextant

Measurement of time

Meridian altitudes

Sun, star and other sights

Compass checking

Great circle sailing


Passage planning

Passage making


  • Definition of observer’s zenith and position of a heavenly body in terms of latitude, longitude, GHA and declination
  • Right angle relationships, latitude and co-late, declination and polar distance
  • Relationship between GHA, longitude and LHA
  • Tabulation of declination in nautical almanac
  • Rate of increase of hour angle with time
  • The tabulated components of the triangle, LHA, co-lat and polar distance
  • The calculable components, zenith distance and azimuth
  • Relationship between zenith distance and altitude
  • Introduction to the tabular method of solution in the Air Navigation Tables and the basic sight form
  • The use of calculators for the solution of the PZX triangle
  • Practical guide to the use and care of a sextant at sea
  • Conversion of sextant altitude to true altitude
  • Application of dip, index error and refraction
  • Correction of side error, perpendicularity, index error and collimation error
  • Definition of, and relationship between, UT, LMT, standard time and zone time
  • Rating of chronometers and watches
  • Forecasting time of meridian altitude
  • Reduction of meridian altitude sights
  • Reduction and plotting of sun sights using Air Navigation Tables
  • Awareness of use of calculator for sight reduction
  • The plotting of a sun-run-sun meridian altitude
  • Awareness of the reduction and plotting of sights obtained from stars, moon and planets
  • Use of amplitude and azimuth tables systems and/or calculator
  • Satellite Navigation Systems
  • Principles and limitations of use of all systems
  • Comparison of rhumb lines and great circles
  • Vertices and composite tracks
  • The computation of a series of rhumb lines approximating to a great circle by use of gnomonic and Mercator projections
  • General pressure distribution and prevailing winds over the oceans of the world
  • Tropical revolving storms, seasonal occurrence and forecasting by observation
  • Publications available to assist with planning of long passages (routeing charts, ocean passages of the world and other publications)
  • Preparation for ocean passage including survival equipment, victualling, water and fuel management, chafe protection, spares and maintenance
  • Navigational routine
  • Watch-keeping
  • Crew management
  • Satellite and terrestrial systems
  • Weather information

You will need a set of dividers which you will probably have from the Yachtmaster Shorebased course. We can provide them for £20. Alternatively you can buy them from most chandleries but they will probably be more expensive. You will be asked if you want us to supply you with this item when you book a course.

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