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CALIBRATION
Milepost run
It is common practice to check a new ship's performance at an official trial run. Take this
opportunity to calibrate the DS-80.
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. A
B in the illustration. Speed is
obtained from the following equations. Note that Sg1 and Sg2 are both speeds over the ground
(SOG); however the DS-80 provides the speed through the water. To find the speed though the
water, a return trip is necessary.
P1'
P2'
P1
P2
A
B
Sg1 = d/t1 X 3600 (kn).........(1)
Sg2 = d/t2 X 3600 (kn) .........(2)
Sw + St = Sg1 (kn) ......... (3)
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),
AP-1
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