AP-1
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. A
→B 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.
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.
P1
P1'
P2
P2'
A
B
d
Sg1
Sg2
Transit posts
Transit posts
