Module 6 - Position, Course & Speed
True Bearings, Courses, DR and EP
What you will learn
Keep bearing, course, heading, water track and ground track distinct, then carry a known position forward as a labelled DR or EP without presenting an estimate as a fix.
Direction labels explain what the vessel, water and seabed are doing. DR and EP preserve the same discipline by exposing which movement was observed, calculated or assumed.
Navigational directions run clockwise from north: 000°/360° north, 090° east, 180° south and 270° west. A bearing gives the direction of an object or line from a stated north reference. Course is a selected direction of travel, heading is where the fore-and-aft line points, water track includes leeway, and ground track also includes current. These terms are related but not interchangeable.
Write T, M or C wherever the reference could be ambiguous. True is referenced to True North, magnetic to Magnetic North and compass to the vessel's compass after local deviation. A corrected true bearing of 045°T from the vessel to a lighthouse plots from the known lighthouse on the reciprocal 225°T.
In this lesson convention, a DR advances the last established position using course and distance through the water. An EP modifies that estimate with relevant information such as tidal stream or leeway. Both need time and method labels. Plotting symbols vary between organisations, so follow the stated convention and never rely on an unexplained shape.
Every estimate carries uncertainty from its starting position, steering, log, leeway and stream. Near danger, shorten the interval and obtain independent position evidence rather than allowing a neat vector endpoint to claim more certainty than the inputs support.
Worked example
From a 1200 fix, the yacht makes 060°T through the water at 6 kn for 40 minutes. The supplied stream sets 150°T at 1.5 kn.
- 1Convert 40 minutes to 40 ÷ 60 = 0.667 hour.
- 2DR distance = 6 × 0.667 = 4.0 M on 060°T.
- 3Tidal drift = 1.5 × 0.667 = 1.0 M on the supplied set of 150°T.
- 4The boat vector contributes about 3.464 M east and 2.000 M north; the tide contributes 0.500 M east and 0.866 M south.
- 5Net displacement is about 3.964 M east and 1.134 M north: approximately 4.12 M on 074.0°T from the 1200 fix.
Sense check: A south-easterly tide should turn the 060°T through-water movement towards the east and slightly south, not towards the north-west.
| Quantity | Meaning | Typical evidence |
|---|---|---|
| Heading | Where the bow points | Compass or heading sensor |
| Water track | Path through the water after leeway | Heading plus observed/estimated leeway |
| Ground track / COG | Movement over the seabed | Successive positions or vector result |
| DR | Course-and-distance estimate | Starting position, heading/course and log |
| EP | DR modified by relevant estimated effects | DR plus stream, leeway or other information |
Explain an off-track vessel without changing the labels
The compass heading is steady at 082°C, the water track estimate is 088°T and GNSS COG is 101°T.
1. Keep each reference
Do not compare 082°C directly with true or ground directions until variation and deviation are applied to obtain a true heading.
2. Separate effects
Use estimated leeway to relate heading to water track, then current to relate water track to ground track.
3. Test the explanation
Compare the predicted ground movement with fixes, depth, radar or visual evidence; do not force every discrepancy into a tidal explanation.
Sense check: A direction chain is useful only when every value states its north reference, time and physical meaning.
Common mistake or limitation
- Using course, heading and track as synonyms and hiding the very effects the calculation is meant to expose.
- Calling an EP a fix or assuming one universal DR/EP symbol applies to every organisation.
- Applying leeway once to the water track and again as a separate vector.
Recap
- Directions need a physical meaning and north reference.
- A reciprocal reverses one line by 180°.
- DR and EP are reconstructable estimates, not fresh observed fixes.
- Shorter intervals and independent observations protect decisions near danger.
Optional quick check
Section 2 of 8
Which statement makes an EP reviewable without claiming it is a fix?
Sources and factual review
Reviewed 20 August 2026 - Compass Revision editorial review.
- RYA Coastal Skipper/Yachtmaster Offshore Theory Course
- MCA MGN 610 Amendment 1 — navigation and SOLAS Chapter V
- MCA MGN 379 Amendment 1 — electronic navigational aids
- IHO S-4 chart specifications, edition 4.10.0
- BIPM SI Brochure, ninth edition
- USCG Boat Crew Handbook — Navigation and Piloting
- GPS Standard Positioning Service Performance Standard, fifth edition
Connect bearings to chartwork
Once true bearings are clear, practice measuring distance, plotting positions, and converting courses for compass work.