
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
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
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.