APPENDIX 1 CALIBRATION

Milepost run

It is common practice to check a new ship’s performance at an official trial run. Take this op- portunity to calibrate the DS-60. In practice, the ship speed is evaluated as follows.

1. Calculation with transit posts

Steer the ship at a steady speed on the test course, e.g. AB in the illustration. Speed is ob- tained from the following equations. Note that Sg1 and Sg2 are both speeds over the ground (SOG); however the DS-60 provides the speed through the water. To find the speed through the water, a return trip is necessary.

P1'

P2'

Transit posts

Transit posts

P1

P2

 

 

d

Sg1

Sg2

AB

Sg1 = d/t1 X 3600 (kn)... (1) Sg2 = d/t2 X 3600 (kn)... (2) Sw + St = Sg1 (kn)... (kn3)

Sw - St = Sg2 (kn)... (4) Adding (4) and (3), we get; 2Sw = Sg1 + Sg2 (kn)

Therefore, Sw = (Sg1 + Sg2)/2 (kn)... (5) where,

d = distance run (nm),

t1 = time taken to run 1 (second),

t2 = time taken to run 2 (second). (Note: Runs 1 and 2 are in opposite direction.) Sw = Speed through the water (kn),

St. = Speed of tide current (kn), Sg1 = SOG for run 1 (kn), Sg2 = SOG for run 2 (kn).

Thus we can find a speed through the water by making a round tip.

AP-1

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Furuno DS-60 installation manual AP-1, Milepost run, Calculation with transit posts