Maneuvering Boards Review Maneuvering Boards Review AGENDA Definition

Maneuvering Boards Review

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)

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

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

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

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

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

RELATIVE N BEARINGS Ship’s course = 045 T 000 R 180 R E 0 R 09 W 135 T S

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° + 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 … – Formation Steaming … – RDVU/Intercept … – Wind Problems … CPA’s Station Keeping UNREP’s Desired wind

The Maneuvering Board • 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 Relative Plot • The maneuvering board (relative plot). – E - reference ship (placed in the center) – M 1, M 2 - any maneuvering ship – DRM - Direction of Relative Motion – MRM - Measure of Relative Motion – SRM - Speed of Relative Motion – CPA - Closest Point of Approach

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

Setting up a Mo. Board • First Determine Scale – Speed – Distance

D S

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

D S r e

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

D M 1 S r e

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

D M 1 S M 2 r e

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 M 1 and M 2 (points on the moboard the correspond to the bearings and ranges of the contact)- note, use a 2: 1 scale. 2. Find DRM - 073ºT

D M 1 S M 2 r e

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 M 1 and M 2 (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

D S MRM M 1 M 2 r e

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

D S MRM M 1 M 2 r e

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

D S 343 T MRM M 1 90 r M 2 e

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

D S MRM CPA Range M 1 M 2 r e

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 M 2 & 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 M 2 to find CPA time)

D S MRM CPA Range M 1 M 2 r e

Questions?