Furuno DS-80 - Calibration; Milepost Run; Calculation with Transit Posts

AP-1
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 through the water, a return trip is necessary.
P1
P1'
P2
P2'
A
B
Transit Posts
Transit Posts
d
Sg1
Sg2
St
Sg1 = d/t1 X 3600 (kt)……..(1)
Sg2 = d/t2 X 3600 (kt)……..(2)
Sw + St = Sg1 (kt)…..(3)
Sw – St = Sg2 (kt)…..(4)
Adding (4) and (3), we get;
2Sw = Sg1 + Sg2 (kt)
Therefore, Sw = (Sg1 + Sg2)/2 (kt)….(5)
where,
d = distance run (nm),