Navigation answers three questions: where am I, where am I going, and how do I get there safely? Learn to read a chart, give a position, use the compass and plan a passage, then practise speed, distance and time.
The three questions
Where am I? Where am I going? How do I get there safely? Everything in navigation answers one of these. You work it out with a chart, a compass, a clock and your eyes. Electronics help, but they can fail.
Learn the paper chart first
A chartplotter or phone is wonderful until the battery dies or the screen floods. A sailor who understands the paper chart can use any electronic one, and still find the way home when it fails. Keep a paper chart and a hand compass on board.
Charts differ, so check yours
Colours, symbols, units and rules differ between countries and chart makers. Depths may be in metres, fathoms or feet, and the buoys follow the local system (more in the buoyage lesson later). Always read the chart title and the key (often called Chart No. 1 or the symbol sheet) for your own area.
Speed, distance and time
Slide the speed and the time and watch the boat. Then try the practice questions. The three formulas are all you need.
Distance = speed × time
Time = distance ÷ speed
Speed = distance ÷ time
Your turn
Plan a passage
You want to sail from one harbour to another. Tap the planning steps in the order you would do them. Each right tap locks in; a wrong tap gives you a hint.
A harbour chart
A grid of latitude and longitude, with a boat position
The compass: north, variation, heading and bearing
Planning one passage
Study sheet
All the words in one place, by level.
Level 1: Land and water
Land
Shown in tan or yellow. The coastline is the edge where land meets water. Hills, towers and buildings on the land help you recognise where you are.
Shallow water
Usually a blue tint. Lighter or white means deeper water. Where the colour turns blue, read the depth numbers before you go in.
Soundings
The small numbers are depths. Most modern charts use metres, but some use fathoms or feet, so check the chart. They are measured from chart datum, a low-water level, so the water is usually deeper than the number, but the tide changes it all the time.
Rock
A cross with a dotted ring marks a rock. Some always show, others hide just under the surface. Stay well clear, and remember that the tide can cover them.
Wreck
A sunken ship. It can tear a keel or trap an anchor. Keep away unless the chart shows plenty of depth over it.
Level 2: Marks and tools
Light
A lighthouse or light is drawn with a magenta flare and a note of its pattern, such as Fl(2) 10s: two flashes every ten seconds. By day you know it by its shape, at night by its flashes.
Buoys
Floating marks for channels and dangers. Colour and shape tell you which side to pass. In Region A, red is on your left (port) when you come in from the sea. In Region B it is the other way round. A later module explains buoyage properly.
Anchorage
An anchor symbol marks a place where boats can anchor. A good one has shelter from the wind and waves, holding ground like sand or mud, and enough depth. The chart can also show where anchoring is forbidden.
Scale bar
Shows how a distance on the chart relates to the real sea. For measuring distance on a navigation chart, use the latitude scale on the side, level with your route. The scale can change from the top to the bottom of a chart.
Compass rose
A circle printed on the chart with degree marks. You use it to read and draw courses. On many charts the outer ring is true north and the inner ring is magnetic north, with the local variation written in the middle.
Level 3: Where am I?
Latitude
Imaginary lines running east to west around the Earth. They are measured in degrees north or south of the equator, from 0 to 90. Latitude tells you how far north or south you are.
Longitude
Imaginary lines running from pole to pole. They are measured in degrees east or west of the line through Greenwich, England, from 0 to 180. Longitude tells you how far east or west you are.
Position
Your place on the Earth, given as a latitude and a longitude together, such as 9° 43.5′ N, 100° 02.5′ E. A degree has 60 minutes, and sailors write the minutes with a decimal. Your GPS shows it on the screen.
Nautical mile
One minute of latitude is one nautical mile, about 1,852 metres. That is why sailors measure distance on the latitude scale at the side of the chart. One degree is 60 minutes, so 60 nautical miles.
Knot
A speed of one nautical mile per hour. A boat doing 5 knots goes 5 nautical miles in an hour. Do not say "knots per hour", because the "per hour" is already in the word.
Level 4: The compass
True north
The direction of the geographic North Pole. Charts are drawn with true north at the top. Written as a bearing: 000° T.
Magnetic north
The direction the needle of a magnetic compass points. It is not at the same place as the true North Pole, and it moves slowly over the years.
Variation
The angle between true north and magnetic north where you are. It is printed on the chart, for example "variation 4° E", and it changes with the place and the year. Here it is drawn much bigger than it really is. Memory aid: "Variation west, compass best. Variation east, compass least." It means the magnetic bearing is bigger than the true one when the variation is west, and smaller when it is east.
Heading
The direction the bow points right now, read from the compass. It can differ from the direction you really travel, because wind and current push the boat sideways.
Bearing
The direction from you to something else, such as a lighthouse, measured in degrees clockwise from north. 000° is north, 090° east, 180° south and 270° west.
Level 5: Plan the passage
Waypoint
A point on your route where you turn or check your position. Plan a passage as a list of waypoints joined by straight legs. Keep every waypoint clear of danger.
Track
The line you want to follow over the sea floor, drawn on the chart between waypoints. It is also the line you have really followed. It is the path over the ground, not where the nose points.
Distance
How far a leg is, measured on the chart in nautical miles with dividers on the latitude scale at the side. Add the legs for the whole trip.
Course to steer
The compass course you actually steer to stay on the track, after allowing for current or wind pushing you sideways. If the current pushes you south, you aim a little north of the track.
Set and drift
Set is the direction a current flows toward. Drift is its speed in knots. Together they tell you how hard and which way the sea is moving you.
ETA
Estimated time of arrival: when you expect to get there. Divide the distance by your speed to get the time, then add it to the departure time. Check it again as the trip goes on.