Furuno CI-68 - Manual (Page 67)

PRINCIPLE OF OPERATION
AP-11
In the water tracking mode, watermass just below the transducer (near-surface layer) is
taken as the base of all measurements (virtual ground). Therefore, the ship and tide speeds
in the water tracking mode are not absolute but relative to this near-surface layer.
Vw = 9 kt (Ship’s speed based on near-surface layer)
Vwa = 8 kt (Ship’s speed based on layer A)
Vwb = 5 kt (Ship’s speed based on layer B)
:Base of measurement
Layer A
Start of
trip End of
trip
10 NM (1 hour trip)
Layer B
2 kt
5 kt
Near-
surface
layer
1 kt
Assume that the ship and all measuring layers
are moving in the same direction, but at different
speeds.
3 2 1