This document discusses principles of dead reckoning and current sailing used for navigation at sea. It defines key terms like dead reckoning, course, speed, set and drift of currents. It provides rules of thumb for calculating distance traveled based on speed and time. Examples are given for using course, speed and current information to calculate courses and speeds to achieve desired tracks and speeds over ground.

1. Light 9 9 9 9 9 9 9 9 9 9 9 5 5 5 5 11 11 11 11 11 11 11 11 6 pa FL 6s 58ft 9M Tank Long Point 20 20 20 20 20 20 21 20 20 20 21 21 21 21 21 21 23 23 23 23 23 23 15 15 15 15 17 17 17 17 19 19 19 19 C- 085 T S - 12 0800 0810 0810 Fundamentals of Naval Science Dead Reckoning and Current Sailing

2. Dead Reckoning DR - Determining the position of a vessel by adding to the last fix the ship’s true course and speed for a given time.

3. Dead Reckoning Uses: Determine when change course/speed To predict the time of sighting lights and other aids to navigation Project future positions relative to hazards Measure the effects of current (winds, seas) Alter course to account the effects of current

4. Six Rules of DR

5. Plot a DR Position Every Hour on the Hour 0900 1000 1100

6. Plot a DR Position at Every Course Change 20 24 29 C-125 c-090 C-080

7. Plot a DR Position at Every Speed Change 15 21 27 S-10 S-15 S-5

8. Plot a DR Position for Every Line of Position (LOP) Tank 0826 0826 c-195 s-10

9. Plot a DR Position for Every Fix or Running Fix 46 37 0937 R-Fix 0846

10. 52 58 A new course line shall be drawn from every fix with 2 DRs at your fix interval 0846 c-106 s-10

11. Typical DR plot

12. Speed-Time-Distance Calculations using a nautical slide rule, electronic calculator, set of pre-computed tables, or speed nomogram. D = S x T where: D = distance traveled S = speed in knots T = time in hours

13. Three Minute Rule In 3 minutes a vessel travels in yards a distance 100 times its speed in knots. D = S x 100 where: D = distance traveled (yds) S = speed in knots

14. Six Minute Rule In 6 minutes a vessel travels in miles a distance equal to its speed in knots divided by 10. D = S / 10 where: D = distance traveled (nm) S = speed in knots

15. Current sailing

16. Terms Used in Current Sailing Track (TR) Speed of Advance (SOA) Course (C) Speed (S)

17. Terms Used in Current Sailing Set (S) Drift (D) Course Made Good (CMG) Speed Made Good (SMG)

18. Present DR Position Previous Fix Position Course & Speed Vector Set & Drift Vector Present Fix Position CMG & SMG Vector Actual Current Triangle

19. Future DR Position Previous Fix Position Course & Speed Vector Anticipated or Expected Current Vector Estimated Position at Future Time Track & SOA Vector Estimated Current Triangle

20. 0700 Fix Position Computing Set & Drift 0730 DR Position Course & Speed Vector 0730 Fix Position CMG & SMG Vector c - 090 T s - 12 kts Actual Current Direction Set & Drift Vector Set = 190 T Drift = 2 kts Distance = 1 NM

21. Example Given the course and speed of the ship, and the estimated set and drift, find the anticipated track and the anticipated SOA. C - 090 T S - 12 knots D - 225 T S (set) - 3 knots

22. Example (TR - 102 T) (S - 10.1 kts) c - 090 T s - 12 kts Set - 225 T Drift - 3 kts

23. Example Given the set and drift of the estimated current is 045 T at 3 knots, and the desired track and SOA are 090 T at 12 knots, find the course and speed needed to make the track and SOA good.

24. Example (C - 102 T) (S - 10.2 kts) Set - 045 T Drift - 3 kts TR - 090 T SOA - 12 kts

25. Sensibility Check 1. Current pushing ahead, decrease speed. 2. Current pushing astern, increase speed. 3. Current pushing left, steer more to the right. 4. Current pushing right, steer more to the left.