Determining Gyro Error by Trial and Error
The Franklin technique is extremely useful just prior to getting a ship
under way. The Franklin technique provides an alternative and must be
used if the gyro error cannot be checked by another method prior to
getting under way. To determine gyro error using the Franklin
technique follow the steps in the table and refer to figure 2-22.
Select three to five navaids from the chart. For the best results,
the selected navaids should be about 120 apart. (The ship must
be pierside or anchored, large towers and conspicous buildings
may be selected).
Compare the repeater(s) to be used against the master gyro; note
Take a round of bearings on the selected navaids, and apply any
repeater error to the bearing.
Example: The repeater reads 187° and the master gyro reads
187.5°. The repeater is reading ½° less than (compass least error
east). Since the error is 0.5° east (less than), 0.5 must be added to
all bearings taken from that repeater.
Plot the corrected bearings on the chart with the PMP set for 0°
Observe how the lines intersect, if they meet in a point the gyro is
ON and has no error. If the lines do not intersect, subtract or
add 1.0° at a time until the triangle closes. The amount of
correction is the total gyro error. Log it in the deck log and
Magnetic Compass Record Book.
Figure 2-22. Determing gyro error by adjusting bearings.