Furuno BB FAR28x7 - Manual (Page 140)

3. ARP OPERATION
3-8
The plotting symbol is drawn by broken lines during the initial acquisition stage.
A vector appears in about one minute after acquisition indicating the target's
motion trend. If the target is consistently detected for three minutes, the plotting
symbol changes to a solid circle. If acquisition fails, the target plotting symbol
blinks and disappears shortly.
ARP
Symbol
Meaning
Immediately after acquisition, this plotting symbol is shown in
broken lines.
Within 20 scans (3 s for HSC with antenna running at 42 rpm)) of
the antenna after acquisition, a vector appears to show a trend of
movement.
Within 60 scans (20 scans for HSC with antenna speed of 42 rpm)
of the antenna after acquisition, the plotting symbol changes to a
small circle, indicating steady-state tracking condition.
Note 1: For successful acquisition, the target to be acquired should be within 0.2
to 32 nm from own ship and not obscured by sea or rain clutter.
Note 2: When the capacity for manual acquisition is reached, the message
“TARGET-FULL(MAN)” is displayed at the screen bottom. Cancel
tracking of non-threatening targets if you wish to acquire additional
targets manually.
Note 3: Target number is normally not shown. On the A, B, C and W type radars
it appears when the cursor is placed on an ARP symbol.
CAUTION
Target Swap
When a target being tracked nears another
target being tracked, the targets may be
"swapped". When two targets acquired
either automatically or manually come close
to each other, one of the two may become
a Lost Target. Should this happen, manual
re-acquisition of the Lost Target may be
required after the two have separated.