Furuno CI-80 - Manual (Page 10)

6
Assuming that the ship, layer A and layer B are moving in the
same direction, and ship’s speeds based on layer A (Vwa) and
on layer B (Vwb) are measured as;
Vwa = 8 kt (Ship’s speed based on layer A)
Vwb = 5 kt (Ship’s speed based on layer B)
Tide differential calculations in ground tracking mode
As an absolute ship’s speed (Vg) is available in the ground
tracking mode, tide speeds of layer A (C1) and layer B (C2)
based on ground are calculated as follows:
C1 = Vg - Vwa (Speed of layer A based on ground)
C2 = Vg - Vwb (Speed of layer B based on ground)
Thus, the tide differential (Cd) between layer A and layer B is;
Cd = C2 - C1
= (Vg - Vwb) - (Vg - Vwa)
= Vwa - Vwb
= 8 - 5
= 3 (kt)
or
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)
Tide differential based
on layer A
Speed of layer B
viewed from layer
A
Tide differential based
on layer B
Speed of layer A
viewed from layer
B