Maneuvering Boards Review

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Maneuvering Boards Review
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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)

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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.

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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

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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.
• Ships heading (T)
• Relative Bearings (?R) direction measured with
  reference to the ships longitudinal axis.

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Line of Sight

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

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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

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N
TRUE BEARINGS
000T
Ships course 045T

?
E
W
090T
135T
S
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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

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Remember

• Never plot relative bearings on a maneuvering
  board
• Must convert relative bearings to true bearings
  before plotting

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RELATIVE BEARING
N
270R
E
W
090T
180R
000R
090R
180 T
S
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N
RELATIVE BEARINGS
Ships course 045T
?
E
W
?
?
135T
S
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N
RELATIVE BEARINGS
Ships course 045T
000R
E
W
090R
180R
135T
S
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Converting True and Relative Bearings

• Converting relative bearing to true is
  accomplished by using the following formula

TB SH RB

• Example Contact bears 270R, ship is on course
  330T. What is the true bearing to the contact?

TB SH RB TB 330 270 TB
600 ? 240T
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The Maneuvering Board

• Purpose a tool to plot the position of a ship
  relative to the position of another ship.
• Applications
• Collision Avoidance CPAs
• Formation Steaming Station Keeping
• RDVU/Intercept UNREPs
• Wind Problems Desired wind

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The Maneuvering Board

• Description
• Ten concentric circles
• Bearing lines radiating from the center.
• Five scales provided.
• Nomogram provided.

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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.

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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

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Closest Point of Approach (CPA)

• Made up of three parts
• Range/Distance
• Bearing
• Time

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Setting up a MoBoard

• First Determine Scale
• Speed
• Distance

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Setting up a MoBoard

• Second plot yourself in the center of the MoBoard
• Then plot your ships
• Speed
• Distance
• For Example you are on a course of 050T at a
  speed of 15 kts.

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r
e
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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 21 scale.

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r
M1
e
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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 21 scale.

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M2
r
M1
e
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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 21 scale.
• 2. Find DRM - 073ºT

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M2
r
M1
e
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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 21 scale.
• 2. Find DRM - 073ºT
• 3. Find MRM - 7,500 yards

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MRM
M2
r
M1
e
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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

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MRM
M2
r
M1
e
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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

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343T
MRM
90
M2
r
M1
e
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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

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MRM
CPA Range
M2
r
M1
e
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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)

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MRM
CPA Range
M2
r
M1
e
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Questions?