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1-7
Cd = C1 - C2
= (Vg - Vwa) - (Vg - Vwb)
= Vwb - Vwa
= 5 - 8
= -3 (kt)
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
w
e
Layer A
Start of
trip
End of
trip
10 NM (1 hour trip)
Layer B
2 kt
5 kt
q
Near-
surface
layer
1 kt
Assume that the ship and all measuring layers
are moving in the same direciton, but at different
speeds.
Tide differential based on layer B
Speed of layer A viewed from
layer B