Tracking Bearing Drift, Target Angle

• AGENDA:– Basic Tracking– Determination of CPA’s– Bearing Drift– Target Angle– Contact Reports

• Applicable reading: MBW Ch 5.

Tracking, Bearing Drift, Target Angle

Solving the Contact Tracking Problem:1. Read the entire problem and decide on scale.

2. Use the largest scale possible that will permit the entire problem to be plotted on the maneuvering board.

3. Once you have selected a scale, be consistent in its use.

Basic Tracking

Solving the Contact Tracking Problem:4. Plot the M1, M2, etc.; avoid plotting reciprocals.

When a bearing is given, be sure you understand to which ship the bearing applies, and from which ship the bearing is observed. The successive positions M1, M2, etc., indicate movement or maneuvering relative to the reference ship.

Basic Tracking

Solving the Contact Tracking Problem:At 0800 a contact bears 280ºT, at a range of 16,000

yards. At 0815 the same contact bears 300ºT, at 10,000 yards:

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

Basic Tracking

M1M2

D S

Solving the Contact Tracking Problem:5. Solve for DRM, MRM, SRM.

a. DRM - Solved for measuring true bearing between M1 and M2.

b. MRM - Computed using dividers. Spread betweenM1 and M2 and measure the distance using the same scale used for plotting M1 and M2.

c. SRM - Computed by dividing distance (MRM) by the amount of time between M1 and M2.

Basic Tracking

M1M2

MRM

e

D SD

Solving the Contact Tracking Problem:At 0800 a contact bears 280ºT, at a range of 16,000

yards. At 0815 the same contact bears 300ºT, at 10,000 yards:

5a. Find DRM - 073ºT

5b. Find MRM - 7,500 yards

5c. Find SRM - 15 knots

Basic Tracking

Solving the Contact Tracking Problem:6. Plot your course and speed vector (er). “e” is the

point from which all actual (true) course and speed vectors are drawn (center of moboard sheet). “r” is the reference ship. The direction of this vector is the reference ship’s true heading and the magnitude is the speed over time.

Basic Tracking

M1M2

MRM

r

e

D S

Solving the Contact Tracking Problem:7. Parallel the DRM line to the tip of your course

vector er and measure the length of SRM along the DRM to form the second side of the speed triangle. This vector is labeled “rm” with point “m” being the maneuvering ship.

Basic Tracking

M1M2

MRM

r m

e

D S

Solving the Contact Tracking Problem:8. Solve for the maneuvering ship’s course and

speed by connecting points “e” and “m”. The direction of this vector is the maneuvering ship’s course and speed is simply the length of you “em” vector (measured on your speed scale).

Basic Tracking

Solving the Contact Tracking Problem:At 0800 a contact bears 280 T, at a range of 16,000

yards. At 0815 the same contact bears 300 T, at 10,000 yards. Your course is 135 T at 15 knots:

8. em - 103 T, 26 knots

Basic Tracking

M1M2

MRM

r m

e

D S

Solving the Contact Tracking Problem: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 and range:

9a. CPA bearing (Add or subtract 90º to/from DRM to determine CPA Bearing) - in this case subtract 90º:

073ºT - 090ºT = 343ºT

Basic Tracking

M1M2

MRM

90

SD

Solving the Contact Tracking Problem: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 and range:

9b. CPA Range - measure from the center of the maneuvering board to CPA point to determine CPA range - 7,500 yards

Basic Tracking

M1M2

MRM

CPA Range

SD

Target Angle:

• Target angle is defined as your relative bearing FROM another ship. In other words, it is what aspect of him you are seeing.

• It allows the shiphandler to determine which aspect of another ship is in view and determine if a risk of collision exists.

Target angle = True Bearing +/- 180 - contact’s course

Target Angle

Target Angle Practical

Bearing Drift:

Bearing Drift is the amount of change of a contact’s bearing over a period of time. If the bearing of a contact does not change over time and the range is decreasing, there is a definite risk of collision occurring. If there is a definite change in bearing over time then there is little or no risk of collision.

Bearing Drift

0800

0810

S

09000920

S

1000

1030

S

Captain, this is the officer of the deck. I have a contact report. I have a [ID] ...

“off the starboard bow bearing 033ºR, range 10,000 yards. His target angle is 305º and has steady left visual bearing drift. He is moving towards a CPA 10º off the port bow at a range of 2000 yards in 20 minutes. I evaluate this as a crossing situation, we are the give-way vessel. I recommend coming right to new course ___. This will open the contact’s CPA to 5,000 yards.”

Contact Reports