Navigation

NAU 102

Lesson 18

Gyro Error

Properly adjusted, gyro errors seldom exceed 1°

Any error will be the same on all headings.

Determining Gyro Errors

Comparing gyro bearing to charted true bearing of a range or object.

Comparing gyro bearing to computed true bearing of a celestial object.

Trial and error adjustment of bearings of 3 lines of position.

Comparison with a compass of known error.

Gyro Error

Gyro Error is labeled East (E) if the gyro points to the east or right of the

true meridian.

Labeled West (W) if the gyro points to the west or left of the true

meridian.

Memory Aid

“Naming” Gyro Error

Compass Least, Error East

Compass Best, Error West

Example

If the true bearing of a light is 161° T and the gyro bearing is 159.5° pgc (per gyro

compass), what is the gyro error?

T

G

161° T

159.5° pgc

1.5°E or W?E

Example

3 LOP’s from Gyro Bearings

Example

Add 1° to each bearing

Example

Gyro Error = 1° W

Subtract 1° from each bearing

Applying Known Error

Once error is determined, it should be applied to all gyro directions.

GET

Gyro + East = True

Therefore, Gyro - West = True

And, True - East = Gyro

Example

You are steering course 195° pgc. The gyro error is 2° W. What true course are

you making good?

G

+E

T 193°

2° W195°-

Homework Problem #1The true course between two points is 057°. Your

gyrocompass has an error of 3° east and you make an allowance of 1° leeway for a north-

northwest wind. Which gyro course should be steered to make the true course good?

G

+E

T

054° pgc

3° E

057°T

-054° pgc

1°-

053° pgcAnswer

Homework Problem #3You are steering 154° per gyrocompass. The wind

is northeast by east, causing 4° leeway. The gyro error is 3° east, variation is 11° west, and deviation is 7°E. What is the true course made

good?

G

+E

T

154° pgc

3° E

157°T

+157° T

4°+

161° TAnswer

Deviation Table Construction

One method to determine the deviation of the magnetic compass is to compare it with a gyrocompass of

known error.

Homework Problem #7You are on course 251°pgc and 241° psc, when you

observe a range in line bearing 192°pgc. The chart indicates that the range is in line on a bearing of

194°T. The variation is 16°E. What is the deviation of the magnetic compass?

G

+ET

192° pgc

2°194°T

E (Compass Least)

Step 1 – Determine Gyro Error

Homework Problem #7You are on course 251°pgc and 241° psc, when you observe a range in line bearing 192°pgc. The chart

indicates that the range is in line on a bearing of 194°T. The variation is 16°E. What is the deviation of the

magnetic compass?

G

+ET

251° pgc

2° E253° T+

Step 2 – Compute True Heading

Homework Problem #7You are on course 251°pgc and 241° psc, when you

observe a range in line bearing 192°pgc. The chart indicates that the range is in line on a bearing of

194°T. The variation is 16°E. What is the deviation of the magnetic compass?

TVM

16° E237° M

253° T-

Step 3 – Compute Deviation

DC 241° psc

4° WE or W?

Homework Problem #20

You swung ship and compared the magnetic compass against the gyro compass to find deviation. Gyro error is 2°E. The variation is 8°W. Find the deviation on a

true heading of 187°.

HEADING HEADING HEADING PSC PGC PSC PGC PSC PGC 358.5° - 350° 122.5° - 110° 239.5° - 230° 030.5° - 020° 152.0° - 140° 269.0° - 260° 061.5° - 050° 181.0° - 170° 298.0° - 290° 092.0° - 080° 210.0° - 200° 327.5° - 320°

Magnetic Compasses

Disadvantages

Deviation

No digital output

Gyrocompasses

Disadvantages

Expensive

Difficult and expensive maintenance

Requires stable power and backup

Takes a long time to stabilize

New Advances

Flux Gate Magnetic Compass

Ring Laser Gyrocompasss

•No moving parts•Digital output

•Low power requirements•Rapid start-up•Self correcting

Flux Gate Compass

Two harmonic coils wrapped around a magnetic core.

Earth’s magnetic field changes the core’s magnetic induction.

The coils sense the changes.

Electronics calculate the magnetic field necessary to cause the change.

Flux Gate Compass

Flux Gate Compass

To minimize deviation, the sensor is placed at the top of the mast.

Residual deviation is automatically calculated as the ship changes course 360°.

It makes its own deviation table!

Deviation is automatically applied.

Flux Gate Compass

Operator can input the variation.

Resulting true direction is sent to digital equipment.

Ring Laser Gyrocompass

Two laser beams travel in opposite directions around a fiber-optic ring.

When the compass (the ship) isn’t turning, the beams are in phase.

When the compass turns, the beams are out of phase.

The quicker the turn, the larger the phase differences.

Ring Laser Gyrocompass

Introduction to Navigation

Questions?