Date post: | 24-Dec-2015 |
Category: |
Documents |
Upload: | dwain-bryan |
View: | 246 times |
Download: | 0 times |
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)
Maneuvering Boards Review
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.
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
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.
Line of Sight
• Each line of sight has two directions which differ by 180 degrees
• Heading of either ship does not affect the LOS
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
Ship’s course = 045T
135T
NN
EEWW
SS
TRUE BEARINGSTRUE BEARINGS
000T
090T
?
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
Remember…
• Never plot relative bearings on a maneuvering board
• Must convert relative bearings to true bearings before plotting
NN
EE
SS
WW
090R
180R
RELATIVE BEARINGRELATIVE BEARING
270R
000R
090T
180 T
Ship’s course = 045T
135T
??
NN
EEWW
SS
RELATIVE RELATIVE
BEARINGSBEARINGS
?
Ship’s course = 045T
135T
090R
180R
NN
EEWW
SS
RELATIVE RELATIVE
BEARINGSBEARINGS
000R
• Converting relative bearing to true is accomplished by using the following formula:
Converting True and Relative Bearings
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° + 270°
TB = 600° 240°T
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
Th
e M
aneu
veri
ng
Boa
rd• Description:
– Ten concentric circles
– Bearing lines radiating from the center.
– Five scales provided.
– Nomogram provided.
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.
• 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
The Relative Plot
Closest Point of Approach (CPA)
• Made up of three parts– Range/Distance
– Bearing
– Time
Setting up a MoBoard
• First Determine Scale– Speed– Distance
D S
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.
D S
er
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.
M1
D S
er
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.
M1M2
D S
er
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
M1M2
D S
er
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 - 073ºT3. Find MRM - 7,500 yards
M1M2
MRM
D S
er
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 - 0800 to 0815) to find SRM - 15 knots
M1M2
MRM
D S
er
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 - 0800 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
M1M2
MRM
90
D S
er
343T
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
M1M2
MRM
CPA Range
D S
er
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)
M1M2
MRM
CPA Range
D S
er
Questions?