Furuno CI-68 - Manual (Page 65)

PRINCIPLE OF OPERATION
AP-9
Tide, Nav-tide and Tide Differential
Tide (absolute tide)
Absolute tide can be measured in the ground tracking mode.
:Base of
measurement
Layer A
Fixed
Start of
trip End of
trip
(Moving at 10 kt on ground)
(Moving at 3 kt on ground)
10 NM (1 hour trip)
2
1
Assume that the ship and layer A are moving in the same direction, and ship’s speeds
based on ground (Vg) and on layer A (Vwa) are measured as;
Vg = 10 kt (Ship’s speed based on ground)
Vwa = 7 kt (Ship’s speed based on layer A).
Speed of layer A based on ground (C1) can be calculated as follows:
C1 = Vg - Vwa
= 10 – 7
= 3 (kt)