Module 6 - Position, Course & Speed
Worked DR and EP from Course, Log, and Tide
Worked DR example: at 1000 you fix your position. From 1000 to 1030 you steer 045 degrees true and the log shows 2.5 M through the water. Plot 2.5 M along 045 degrees true from the fix: that is the 1030 DR.
Worked EP example: during the same half hour the tidal stream sets 120 degrees at 2 knots. In 30 minutes the tide moves the boat 1.0 M, because distance = speed x time = 2 x 0.5. Plot 1.0 M in direction 120 degrees from the DR. The end of that tide vector is the 1030 EP.
The exam habit is to label the method and time. If the question asks for a DR, do not include tide. If it asks for an EP, start from the DR and add the estimated external movement, such as tide and leeway.
5 kn x 0.5 h
Result: 2.5 M
2.5 M on 045 degrees true from the fix
Result: 1030 DR
2 kn x 0.5 h
Result: 1.0 M
1.0 M on 120 degrees true from the DR
Result: 1030 EP
| Step | Calculation | Result |
|---|---|---|
| Distance through water | 5 kn x 0.5 h | 2.5 M |
| DR | 2.5 M on 045 degrees true from the fix | 1030 DR |
| Tide drift | 2 kn x 0.5 h | 1.0 M |
| EP | 1.0 M on 120 degrees true from the DR | 1030 EP |
Key points
- DR = course steered and distance through the water.
- Distance = speed x time; 30 minutes is 0.5 hours.
- EP = DR plus tide and leeway estimates.
- Label DR and EP with times so the chart tells a story.
Continue studying Position, Course & Speed
This topic is part of Module 6. Open the full module for lessons, quizzes, flashcards, and revision tools.