Module 6 of 17
Position, Course & Speed
True bearings, courses, latitude, longitude, and the knot.
Latitude and Longitude
Position on the Earth's surface is defined using latitude and longitude. Latitude measures north or south of the Equator (0° to 90°N or S). Longitude measures east or west of the Prime Meridian at Greenwich (0° to 180°E or W).
Each degree is divided into 60 minutes ('). One minute of latitude equals one nautical mile. Position is written as, for example: 50°24'.3N 001°12'.8W. On a chart, latitude is read from the vertical (side) scale and longitude from the horizontal (top/bottom) scale.
Key Points
- Latitude = N/S of Equator (0°–90°)
- Longitude = E/W of Greenwich (0°–180°)
- 1 minute of latitude = 1 nautical mile
- Always measure distance using the LATITUDE scale
- Format: 50°24'.3N 001°12'.8W
Tip: NEVER use the longitude scale to measure distance — only the latitude scale. One minute of longitude is NOT one nautical mile (it varies with latitude).
True Bearings and Courses
A true bearing is measured clockwise from True North (0°/360°) through East (090°), South (180°), and West (270°). All chart work is done in true bearings initially — compass corrections (variation and deviation) are applied afterwards.
A course is the intended direction of travel, expressed as a three-figure bearing (e.g., 045°T). The suffix T, M, or C indicates True, Magnetic, or Compass bearing.
Key Points
- True bearings: measured clockwise from True North
- Always written as three figures (e.g., 005°, 090°, 180°)
- T = True, M = Magnetic, C = Compass
- Charts are oriented to True North
- Compass rose on chart shows both True and Magnetic north
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