Furuno DS-80 Installation Manual page 45

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.
2. Calculation with DS-80
To measure the distance run between points A and B by DS-80, do the following:
1. Reset the distance run figure of DS-80 to zero by selecting ON at RESET on the DISTANCE
RUN DISPLAY menu at the moment the ship passes point A.
2. Run the ship from A to B at full speed, timinh with a stopwatch.
3. Read the distance run (NM) and time taken to run (second) exactly at the moment the ship
passes point B.
4. Run the ship from B to A at full speed reerrinh to step 1 through 3.
Where,
n1 (NM) = distance run from A to B measured by DS-80
n2 (NM) = distance run from B ro A measured by DS-80
Therefore, the average run from A to B measured by DS-80
Therefore, the average ship speeds of run 1 and run 2 are calculated as follows.
Slog1 (kn) = n1/t1 X 3600
Slog2 (kn) = n2/t1 X3600
The average ship speed of round trip is Slog (kn) = (Slog1 + Slog2)/2. ....... (6)
3. Speedlog error
From (5) and (6),
Error = (Sw - Slog)/Slog X 100 (%)..... (7)
This error can be corrected at SPEED OFFSET on the system menu as follows:.
1. Press the [MENU] key.
2. Select SYSTEM MENU and press the [ENT] key.
3. Select SPEED OFFSET and press the [ENT] key.
4. Enter the value of error.
Repeat the above procedure several times to satisfy the speed accuracy specification.
AP-2