RYA Yachtmaster Ocean Theory

RYA Yachtmaster Ocean Theory is the RYA's most advanced shorebased navigation course, written for sailors planning ocean passages. Its core is astro navigation: using a sextant, an accurate clock and an almanac to find your position from the sun, moon, planets and stars, so you can still navigate far from land if the electronics fail. It also covers worldwide weather, including tropical revolving storms, and planning ocean passages.

The RYA sets it at 40 hours of learning plus exam time, in a classroom, online or by distance learning. You need navigation knowledge to Coastal Skipper / Yachtmaster Offshore shorebased standard before you start.

Who it suits

• Skippers and crew preparing for a blue-water passage or an offshore race
• Yachtmaster Offshore holders working towards the Yachtmaster Ocean certificate
• Navigators who want a genuine backup to GPS, and the satisfaction of a sun sight

What you'll actually do

Much of the course is learning to work sights by hand: taking a sextant reading, correcting it, extracting data from the almanac and tables, and plotting the result as a position line. You'll practise the noon sight until it's routine, then sun-run-sun fixes and star sights at twilight. Alongside that you study global wind and current patterns, tropical storm avoidance and how to plan a route and timing for an ocean crossing. The course ends with an exam.

Key ideas explained

• The sextant — it measures the angle (altitude) between a celestial body and the horizon. The raw reading is corrected for instrument error, the height of your eye above the sea (dip) and the bending of light through the atmosphere (refraction) to give a true altitude.
• Time is position — the earth turns 15 degrees an hour, so every four seconds of clock error can put your longitude out by a minute, or up to a mile. Accurate time, and knowing your watch's error, is essential.
• The noon sight (meridian altitude) — when the sun reaches its highest point it lies due north or south of you. Combine that altitude with the sun's declination from the almanac and you get your latitude with a simple sum, no tables needed.
• Position lines by intercept — for other sights you compare the altitude you observed with the altitude calculated for an assumed position. The difference, in minutes of arc, equals nautical miles towards or away from the body, giving a position line. Two or more position lines (from stars, or the sun at different times) give a fix.
• Checking the compass — the sun's true bearing at rising, setting or any time can be calculated and compared with the compass to find deviation mid-ocean.
• Tropical revolving storms and passage planning — cyclones, hurricanes and typhoons are the same phenomenon with regional names. Ocean passages are planned around their seasons (in the southern hemisphere broadly November to April), prevailing winds and currents, often using great-circle routes, which are the shortest distance on a globe.

Where it fits

Getting ready

• Refresh your Offshore-level chartwork and weather before starting
• If you can, borrow or buy a sextant early: taking real sights from a beach or headland makes the theory click
• Be comfortable with angles in degrees and minutes and with adding and subtracting times
• Ask the school which almanac and sight reduction tables they use, and whether practical sextant sessions are included

Good to know in Australia

• Australia's northern waters and much of the South Pacific sit in the cyclone belt, so the tropical storm sessions are directly relevant to popular passages such as those to New Caledonia, Vanuatu and Fiji.
• Leaving Australia by yacht involves customs, immigration and biosecurity formalities that this course doesn't cover, so research them well ahead of an international passage.