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) 1

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. 1

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

N TRUE BEARINGS 000T Ship’s course = 045T ? W E 090T 135T 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 270R E W 090T 180R 000R 090R 180 T S

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

RELATIVE BEARINGS N Ship’s course = 045T 000R W E 090R 180R 135T 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 … CPA’s Formation Steaming … Station Keeping RDVU/Intercept … UNREP’s Wind Problems … Desired wind

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

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) 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

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 r e

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.

D S r M1 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 M1 and M2 (points on the moboard the correspond to the bearings and ranges of the contact)- note, use a 2:1 scale.

D S M2 r M1 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 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

D S M2 r M1 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 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

D S MRM M2 r M1 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 M2 r M1 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 343T MRM 90 M2 r M1 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 M2 r M1 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 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)

D S MRM CPA Range M2 r M1 e

Questions?