Furuno FAR-2107 Operator's Manual page 148

3. TARGET TRACKING (TT)
3. Push the left button to enter the reference mark.
The reference target mark (see below) appears at the cursor position and
the own ship position data label changes from "LOG," "NAV" or "MANUAL" to
"REF." Note that it takes three minutes before a new speed is displayed. If
tracking has failed for a reference target, the target is marked with a lost
target mark (symbol formed with two triangles).
4. Repeat steps 2-3 to continue entering reference marks. Three may be
entered.
Notes on speed input by reference target
• Reference targets are only used for the calculation of true speed.
• Do not use reference target generated true speed to calculate relative speed. Relative
speed data is not accurate because response to speed change is slow, hampering the
TT's ability to accurately judge the possibility of collision.
• Select a stationary target as a reference target to calculate own ship speed as ground
tracking speed. Do not choose a moving target as a reference target. A moving target
produces error in the vector for TT and AIS, which results in wrong collision avoidance
information. Further, an unstable stationary target produces inaccurate speed data and
the target itself may become lost.
• When a reference target is lost or goes out of the acquisition range, that reference target
mark blinks and the indication "REF TARGET LOST" appears in the alert box. If all
reference targets are lost, the speed indication reads "*.*" Select a different reference
target if currently selected one is lost.
• When all targets are deleted, the reference target mark is also deleted and the
target-based speed becomes invalid. The speed is indicated as BTREF where BT
means Bottom Track (speed over ground).
• Reference targets may be marked with a vector. This can be done with 3 REF TARGET
VECTOR on the TT TARGET menu.
• Loss of reference target will affect the calculation of true speed and true course of
targets. Further, own ship speed will be inaccurate.
Canceling echo-referenced speed input
Open the SPD menu, referring to section 1.13, and set 1 SHIP SPEED to LOG,
NAV or MANUAL as appropriate.
3-4
changes to
R1
R1
Reference target
in three minutes