The terms you meet on board, on the plotter and in Manta, in one line each.
- AIS (Automatic Identification System)
- The radio system through which ships broadcast their identity, position, course and speed to everyone around them.
- Apparent wind
- The wind you feel on a moving boat, the true wind combined with the headwind created by the boat's own speed.
- Beam reach
- Sailing with the wind coming from the side, at right angles to the boat.
- Beaufort scale
- The scale from 0 to 12 that describes wind strength by its effects, from calm to hurricane force.
- Broad reach
- Sailing with the wind coming from behind at an angle, over the stern quarter.
- Chartplotter
- A navigation display that shows the boat's GPS position on an electronic chart, often the hub of all instruments on board.
- Close-hauled
- Sailing as close to the wind as the boat can efficiently go, with the sails pulled in tight.
- COG (course over ground)
- The direction in which the boat actually moves over the seabed, measured by GPS.
- Current set and drift
- The direction (set) and speed (drift) of a current, and how the moving water carries the boat off its course.
- Dead reckoning
- Working out your position from a known starting point, your course, your speed and the time elapsed.
- Depth below keel
- The water depth between the bottom of the keel and the seabed, which is how much water you really have under the boat.
- Deviation
- The compass error caused by the boat's own magnetic fields, different on every heading.
- Douglas sea scale
- The scale from 0 to 9 that describes the state of the sea by wave height, from glassy calm to phenomenal.
- GPX (GPS Exchange Format)
- The open file format for exchanging waypoints, routes and tracks between GPS devices and apps.
- Gybe
- Turning the stern of a sailboat through the wind, so the wind comes from the other side and the boom swings across.
- Heading
- The direction the boat's bow is pointing, as shown by the compass.
- Heel
- The sideways tilt of a sailboat, pushed over by the wind in its sails.
- Knot
- The unit of speed at sea, one nautical mile per hour, or 1.852 km/h.
- Leeway
- The sideways drift of a boat through the water caused by the wind, the angle between where the bow points and where the boat goes.
- Logbook
- The record of a boat's voyages, with times, positions, courses, weather and events, written as they happen.
- Magnetic variation
- The angle between true north and magnetic north at a given place, the difference between a magnetic and a true course.
- Nautical mile
- The unit of distance at sea, exactly 1,852 metres, originally one minute of latitude.
- NMEA 0183
- The older marine data standard, with plain-text sentences sent over a serial line, such as $GPRMC for position or $IIMWV for wind.
- NMEA 2000
- The modern marine data network, a CAN bus at 250 kbit/s that connects instruments, plotters and engines with one cable.
- NMEA gateway
- A small device that connects to the boat's NMEA 2000 or NMEA 0183 network and sends its data over WiFi to phones and tablets.
- Okta
- The unit for cloud cover, how many eighths of the sky are covered by cloud, from 0 to 8.
- Polar diagram
- A chart of how fast a boat sails at every wind angle and wind strength, her performance fingerprint.
- Port and starboard
- The left (port) and right (starboard) side of a boat, looking forward toward the bow.
- Reefing
- Reducing the area of a sail so the boat stays under control as the wind gets stronger.
- Route
- A planned course made of waypoints in order, the plan for where you intend to sail.
- Running
- Sailing with the wind directly from behind, dead downwind.
- Significant wave height
- The average height of the highest third of the waves, the wave height that forecasts give and an experienced eye estimates.
- SOG (speed over ground)
- How fast the boat moves over the seabed, measured by GPS, the speed that decides when you arrive.
- STW (speed through the water)
- How fast the boat moves through the water around it, measured by the log, the speed the sails and hull actually produce.
- Tack
- Turning the bow of a sailboat through the wind, so the wind comes from the other side, and the name for the side the wind is on.
- Track
- The recorded path a boat actually sailed, a trail of timestamped positions.
- True wind
- The wind as it blows over the water, independent of the boat's own motion, what a boat at rest would feel.
- True wind direction (TWD)
- The compass direction the true wind blows from, independent of where the boat is pointing.
- VMC (velocity made on course)
- How fast you are closing in on your destination or next waypoint, the part of your speed that points at it.
- VMG (velocity made good)
- How fast you are actually getting upwind or downwind, the part of your boat speed that brings you toward your goal.
- Wave period
- The time in seconds between two successive wave crests passing the same point.
- Waypoint
- A named position, stored as latitude and longitude, used to plan and follow a course.
- Windward and leeward
- Windward is the side the wind comes from, leeward the side it blows toward.