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.

Compass Least, Error East Compass Best, Error West 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? G 159.5° pgc 1.5° E or W? E T 161° T

3 LOP’s from Gyro Bearings Example 3 LOP’s from Gyro Bearings

Example Add 1° to each bearing

Subtract 1° from each bearing Example Subtract 1° from each bearing Gyro Error = 1° W

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 195° - 2° W +E 193° T

Homework Problem #1 G 054° pgc 054° pgc +E - 3° E - 1° 057°T T The 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 054° pgc 054° pgc +E - 3° E - 1° 057°T T 053° pgc Answer

Homework Problem #3 G 154° pgc 157° T +E + 3° E + 4° 157°T T 161° T You 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 154° pgc 157° T +E + 3° E + 4° 157°T T 161° T Answer

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 #7 Step 1 – Determine Gyro Error G 192° pgc +E 2° You 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? Step 1 – Determine Gyro Error G 192° pgc +E 2° E (Compass Least) T 194°T

Homework Problem #7 Step 2 – Compute True Heading G 251° pgc +E + 2° E You 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? Step 2 – Compute True Heading G 251° pgc +E + 2° E T 253° T

Homework Problem #7 T 253° T V - 16° E M 237° M D 4° 241° psc C You 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? Step 3 – Compute Deviation T 253° T V - 16° E M 237° M D 4° E or W? W 241° psc C

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?