1. Maneuvering Boards Review

2. Maneuvering Boards Review
AGENDA:
Definition of Relative Motion
True Bearings vs. Relative Bearings
The Maneuvering Board
The Relative Plot
Application: Example of Collision Avoidance (CPA) 1

3. True vs. Relative Motion
True vs Relative Motion: Understanding the difference between true and relative motion is essential in excelling in moboards.
True Motion: the movement of an object with respect to the surface of the earth.
Relative Motion: the apparent movement of an object with respect to another moving object.

4. Relative Movement Represented on maneuvering board
Consider yourself onboard ship monitoring actions of other ships
Find actual course and speed required to bring about desired change in relative position in maneuvering a ship at sea

5. True vs. Relative Bearings
Line of Sight (LOS) = straight line between an observer and an object.
True Bearings (T) = direction measured with respect to true of geographic north.
Ship’s heading (°T)
Relative Bearings (R) = direction measured with reference to the ship’s longitudinal axis. 1

6. Line of Sight
Each line of sight has two directions which differ by 180 degrees
Heading of either ship does not affect the LOS

7. True Bearings
True Bearing - bearing measured clockwise from true north in degrees to line of sight
heading of ship does not affect bearing
reference line true north remains same regardless of movement

8. N
TRUE BEARINGS
000T
Ship’s course = 045T ? W E
090T
135T S

9. Relative Bearings
Relative Bearing - measured in degrees from ships heading (course) clockwise to the observed object
Remember - course of reference ship will always affect relative bearing because it is reference line for relative bearing

10. Remember… Never plot relative bearings on a maneuvering board
Must convert relative bearings to true bearings before plotting

11. RELATIVE BEARING N
270R E W
090T
180R
000R
090R
180 T S

12. RELATIVE
BEARINGS N
Ship’s course = 045T ? W E ? ?
135T S

13. RELATIVE
BEARINGS N
Ship’s course = 045T
000R W E
090R
180R
135T S

14. Converting True and Relative Bearings
Converting relative bearing to true is accomplished by using the following formula:
TB = SH RB
Example: Contact bears 270°R, ship is on course 330°T. What is the true bearing to the contact?
TB = SH RB
TB = 330° °
TB = 600°  240°T

15. The Maneuvering Board
Purpose: a tool to plot the position of a ship relative to the position of another ship.
Applications:
Collision Avoidance … CPA’s
Formation Steaming … Station Keeping
RDVU/Intercept … UNREP’s
Wind Problems … Desired wind

16. The Maneuvering Board Description: Ten concentric circles
Bearing lines radiating from the center.
Five scales provided.
Nomogram provided.
The Maneuvering Board

17. The Relative Plot
Relative Plot: Defined as a polar representation of the successive positions of one or more moving objects with respect to a reference position. This reference position will normally be your own vessel; the bearings and ranges are taken from your radar.

18. The Relative Plot The maneuvering board (relative plot).
E - reference ship (placed in the center)
M1, M2 - any maneuvering ship
DRM - Direction of Relative Motion
MRM - Measure of Relative Motion
SRM - Speed of Relative Motion
CPA - Closest Point of Approach

19. Closest Point of Approach (CPA)
Made up of three parts
Range/Distance
Bearing
Time

20. Setting up a MoBoard
First Determine Scale
Speed
Distance

21. D S

22. Setting up a MoBoard Second plot yourself in the center of the MoBoard
Then plot your ship’s
Speed
Distance
For Example you are on a course of 050T at a speed of 15 kts.

23. D S r e

24. Example: CPA Determining CPA:
At 0800 a contact bears 280ºT, at a range of 16,000 yards.
1. Plot M1(points on the moboard the correspond to the bearings and ranges of the contact)- note, use a 2:1 scale.

25. D S r M1 e

26. Example: CPA Determining CPA:
At 0815 the same contact bears 300ºT, at 10,000 yards. Find the CPA (bearing, range, and time):
1. Plot M1 and M2 (points on the moboard the correspond to the bearings and ranges of the contact)- note, use a 2:1 scale.

27. D S M2 r M1 e

28. Example: CPA Determining CPA:
At 0800 a contact bears 280ºT, at a range of 16,000 yards. At 0815 the same contact bears 300ºT, at 10,000 yards. Find CPA bearing, range, and time:
1. Plot M1 and M2 (points on the moboard the correspond to the bearings and ranges of the contact)- note, use a 2:1 scale.
2. Find DRM - 073ºT

29. D S M2 r M1 e

30. Example: CPA Determining CPA:
At 0800 a contact bears 280ºT, at a range of 16,000 yards. At 0815 the same contact bears 300ºT, at 10,000 yards. Find CPA bearing, range, and time:
1. Plot M1 and M2 (points on the moboard the correspond to the bearings and ranges of the contact)- note, use a 2:1 scale.
2. Find DRM - 073ºT
3. Find MRM - 7,500 yards

31. D S
MRM M2 r M1 e

32. Example: CPA Determining CPA:
At 0800 a contact bears 280ºT, at a range of 16,000 yards. At 0815 the same contact bears 300ºT, at 10,000 yards. Find CPA bearing, range, and time:
4. Enter nomogram with 7,500 yards and 15 minutes (elapsed time between interval to 0815) to find SRM - 15 knots

33. D S
MRM M2 r M1 e

34. Example: CPA Determining CPA:
At 0800 a contact bears 280ºT, at a range of 16,000 yards. At 0815 the same contact bears 300ºT, at 10,000 yards. Find CPA bearing, range, and time:
4. Enter nomogram with 7,500 yards and 15 minutes (elapsed time between interval to 0815) to find SRM - 15 knots
5. CPA bearing (Add or subtract 90 to/from DRM to determine CPA Bearing) - in this case subtract 90: 073ºT - 090ºT = 343ºT

35. D S
343T
MRM 90 M2 r M1 e

36. Example: CPA Determining CPA:
At 0800 a contact bears 280ºT, at a range of 16,000 yards. At 0815 the same contact bears 300ºT, at 10,000 yards. Find CPA bearing, range, and time:
6. CPA Range - measure from the center of the maneuvering board to CPA point to determine CPA range - 7,500 yards

37. D S
MRM
CPA Range M2 r M1 e

38. Example: CPA Determining CPA:
At 0800 a contact bears 280ºT, at a range of 16,000 yards. At 0815 the same contact bears 300ºT, at 10,000 yards. Find CPA bearing, range, and time:
7. CPA Time - measure the distance between M2 & CPA point. This distance is 6,900 yards. Enter the nomogram with 6,900 yards and an SRM of 15 knots - 14 minutes (add this to time of M2 to find CPA time)

39. D S
MRM
CPA Range M2 r M1 e

40. Questions?