How To Enter Own Ship Speed; Echo-Referenced Speed Input - Furuno FAR-1513 Operator's Manual

3. TARGET TRACKING (TT)
3.6

How to Enter Own Ship Speed

The TT requires own ship's speed and heading data. The speed can be STW, SOG
or echo-referenced speed (based on 3 max. stationary objects). Manual input is also
possible. For automatic or manual input, see section 1.12. For echo-referenced speed
input follow the procedure below.
3.6.1

Echo-referenced speed input

The use of echo-referenced speed is recommended when:
• The speed log is not operating properly or not connected to the radar.
• The vessel has no device (doppler sonar, speed log, etc.) that can measure ship's
bow-stern, port-starboard movement.
If you select echo-referenced speed, the TT calculates own ship's speed relative to a
fixed reference target. The number of targets may be R1, R2 or R3. When a plural of
objects are selected, the mean value is used, for stabilization and speed.
1. Select the operational display area, then press the right button. The [CURSOR]
menu appears.
2. Select [REF MARK], then push the ADJUST knob. The cursor is highlighted.
3. Place the cursor on the location to be used as a reference, then push the ADJUST
knob. The cursor changes from the highlighted cross to a circle with dashed lines,
indicating that the reference location is now set. See section 3.9 for more informa-
tion on TT symbols and their attributes.
The dashed lines of the reference point change to a solid line over time, as shown
in the figure above.
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 mov-
ing target produces error in the vector for TT and AIS, which results in wrong colli-
sion 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 ref-
erence target if currently selected one is lost.
• When all targets are deleted, the reference target mark is also deleted and the tar-
get-based speed becomes invalid. The speed is indicated as "BTREF" where BT
means Bottom Track (speed over ground).
• Reference targets can be marked with a vector.
This can be done with [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.
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