Observed Calculated RunNo. Ship'sCourse Length ofCourseNauticalMiles Time toTravelMeasuredMileMin.-Sec. Time toTravelIndicatedMileMin.-Sec. TrueSpeedKnots LogIndicatedSpeedKnots AverageTrueSpeed AverageLogIndicatedSpeedKnots PercentError 1 311 1 11:30.2 11:03.4 5.22 5.43 5.29 5.49 +3.78 2 131 1 11:10.3 10:49.7 5.37 5.55 3 311 1 4:10.6 3:56.5 14.93 15.23 14.95 15.29 +2.30 4 131 1 4:02.4 3:54.7 14.97 15.35
 The following equations are used for calculating the above data: True speed = (3600 X distance in nautical miles) / (time in seconds to cover measured distance) Time in seconds = (Minutes X 60) / seconds Log indicated speed = (3600 X distance measured on counter) / (time in seconds to record log distance) Average true speed = (Run No. 1 true speed + Run No. 2 true speed) / 2 Average log indicated speed = (Run No. 1 log speed + Run No. 2 log speed) /2 Per cent error = ((Average log indicated speed - Average true speed) X 100 %) / Average true speed Note: The error is positive when the log speed is greater than the true speed. The error is negative when the log speed is less than the true speed. 187
 Figure 14-2. Adjusting diagram for calibrating the Bendix log.

 1. A1 ADJUSTMENT KNOB 2. A2 ADJUSTMENT RING 3. B ADJUSTMENT GEAR KNOB 4. GEAR LOCK KNOB 5. B SCALE 6. WEIGHT ARM 7. INDEX SCREW 8. MAIN BALANCE ARM 9. AUXILIARY BALANCE ARM

Figure 14-5. Weight arm attached to instrument.
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 1. A1 ADJUSTMENT KNOB 2. A2 ADJUSTMENT RING 3. B ADJUSTMENT GEAR KNOB 4. GEAR LOCK KNOB 5. B SCALE 6. WEIGHT ARM 7. WEIGHT 8. INDEX SCREW 9. MAIN BALANCE ARM 10. AUXILIARY BALANCE ARM

Figure 14-6. Weight arm attached to instrument.
the B-adjustment is to be set on the positive side of the B-adjustment scale in the instrument. Set the B-adjustment from the value determined above as follows: Loosen the gear lock knob. Turn the B-adjustment gear knob until the pointer is at the 3.85 position on the negative side of the B-scale. Tighten the gear lock knob.

14A9. Recording the A1-, A2-, and B-adjustments. After setting the A1-, A2-, and

B-adjustments to the values obtained in Sections 14A6, 14A7, and 14A8, record the values obtained in the performed adjustments table in the upper left-hand corner of the adjustment diagram as shown in Figure 14-2.

14A10. Checking A1-, A2-, and B-adjustments with weight and arm. (See Figures 14-5 and 14-6.) After setting and recording the A1-, A2-, and B-adjustments as described in Section 14A9, check the recorded adjustment

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values as follows: Set the maneuvering cocks and vent cocks to the zero position. Set the instrument to zero position by means of the C-adjustment as described in Section 13A4. Hang the weight arm only on the index screw of the main balance arm as shown in Figure 14-5. Note the speed indication obtained, and record it at the upper left-hand corner of the adjustment diagram. Repeat the operation using the weight arm and weight together, as shown in Figure 14-6. When the log is checked at some future time to see if the adjustments have changed due to temperature, spring tension or for some other reason, use the following procedure: Hang the weight arm alone, and then the weight arm and the weight together on the index screw as previously described. Compare   the speed values obtained with the recorded values in the performed adjustments table. If the values are the same within 1/10 knot, the adjustments have not been changed. If the values have changed, check the instrument carefully. See that the contacts are clean, that all connections and screws are tight, that the adjustments have not been changed, and that the instrument generally is in good condition. If the above checks indicate that the instrument is in a satisfactory condition, it will be necessary to make a recalibration run at the earliest possible opportunity, unless the navigator is satisfied with the speed and distance indications obtained. See Section 1413 for information on recalibration.

B. RECALIBRATION OF THE MASTER TRANSMITTER INDICATOR

14B1. Purpose. The purpose of the recalibration run is to correct the log when it is in error. The log may be in error due to one or more of the following reasons: The condition of the hull has been radically changed; the previous run was not properly made, or the instrument and/or rodmeter has been changed in some way.

14B2. Preparation. The preparations described in Section 14A2 for making a measured mile run should be made in this case with the important exception that the A1-, A2-, and B-adjustments are to be set at the same values as last recorded in the performed adjustments table at the upper left-hand corner of the adjustment diagram (Figure 14-7).

14B3. Operation and calculation. (See Figure 14-7). Make the trial runs and calculations as described for the measured mile runs in Section 14A3. Make one additional set of calculations as follows: On the adjustment diagram there appears an adjustment line for the previous trial run. This dotted blue line on the sample diagram (Figure 14-7), is the line from which all plotting and calculations will now be made. At the true speed of 5.20 knots, and at the true speed of 15.40 knots, adjustment factors of 103.8 and 102.25 respectively are obtained. This will then give values which are to be recorded in the following additional table:
 AverageTrueSpeedKnots PercentError AdjustmentFactor CorrectedPercentError 5.20 2.2% 103.8 2.28% 15.40 3.4% 102.25 3.48% Corrected percent error = (Percent error x adjustment factor) / 100

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14B4. Plotting the new adjustment line. (See Figure 14-7.) Plot the new adjustment line as follows: Add algebraically, the corrected percent errors to the adjustment factors at the true speeds obtained, and plot on the diagram as before (see Figure 14-7). In this example, the corrected percent error of 2.28 added to the adjustment factor of 103.8 equals 106.08, and the corrected percent error of 3.48 added to the adjustment factor of 102.25 equals 105.73. Draw the new adjustment line through the plotted points obtained as shown by the solid blue line in Figure 14-7.

14B5. Obtaining A1-value. (See Figure 14-7.) Obtain the new A1-adjustment value by drawing a straight line horizontally across the diagram through the point at which the new adjustment line intersects the zero knot line, and extending it to the A-calibration curve as shown by the solid red horizontal line. Draw a vertical line (solid red) downward from the point at which the previously drawn solid red horizontal line intersects the A curve, to the base line. The reading at this base line point is the value at which the A1-adjustment is to be set (in this case, 4.15).

14B6. Obtaining A2-value. (See Figure 147.) Obtain the A2-adjustment value by counting the .number of divisions between the points at which the old and new adjustment lines intersect the zero knot line on the diagram; in this case 1.5 divisions. That is, the A2-adjustment is to be turned 1.5 divisions from the previous setting in the same direction in which the A1-adjustment knob was turned.

14B7. Obtaining B-value. (See Figure 147.) Obtain the value at which the B-adjustment is to be set in the following manner: Using dividers, measure the distance between the intersection of the solid red horizontal line with the 25-knot line, and the intersection of the new adjustment line (solid blue) with the 25-knot line. Transpose this distance to the scale of diagram. This gives the percentage (value) that the B-adjustment is to be set away from the previous setting. In this case the B setting is minus 0.9. Therefore, the B-adjustment is to be set at minus 4.75.

C. CALIBRATION OF THE LOG WHEN PERCENTAGE ERROR EXCEEDS 8 PERCENT

14C1. Purpose. This method of calibration is to be used only when the log error, determined during trial runs, exceeds plus or minus 8 percent.

14C2. Preparation. Trial runs have been made, and the percent error at certain true speeds determined. Carefully check all the data and calculations before proceeding with this method of calibration.

14C3. Operation and calculation for setting B-adjustment. Set the maneuvering cocks and drain cocks to the zero position. Attach the weight arm, provided in the spare parts box, to the index screw on the main balance arm, as shown in Figure 14-5. Make and hang weights, preferably lead, on the arm so that the speed indications can be run up to the log indicated speeds obtained in the

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 Figure 14-7. Adjusting diagram for recalibrating the Bendix log.

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calculations for the trial runs. Mark each weight for ready identification. Subtract the percent error at a true speed of approximately 5 knots from the percent error at a true speed of approximately 15 knots, and divide this value by 0.4. Then set the B-adjustment to this value on the plus side of the B-scale; if the percent error at 15 knots is greater than the percent error at 5 knots, in a positive direction. Set the B-adjustment on the negative side of the scale   is high at 15 knots, turn the B-adjustment toward a positive, or more positive, reading on the B-scale and try adjusting again.

NOTE: When 5 and 15 knots are mentioned in the above text, they are used merely to indicate the low and high speed runs at which the trial runs were made.

14C5. Calibration when percent error exceeds 8 percent. The following is an example of calibration when the percent error is greater than 3 percent:

 AverageTrueSpeedKnots AverageLog IndicatedSpeed Knots PercentError 5.20 4.65 -10.5% 15.12 13.87 - 8.3%
if the percent error at 15 knots is less than the percent error at 5 knots in a negative direction.