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4. Tracked Target (TT) Operation
4-3
4.4 How to Input Your Ship's Speed
The TT requires own ship's speed and heading data. The speed can be STW, BT, SOG, or echo-referenced speed
(based on 3 max. stationary objects). Manual input is also possible.
For automatic or manual input, see section 2.5 How to Input Your Ship's Speed. For echo-referenced speed input
follow the procedure below.
4.4.1 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 that can measure ship's leeward movement (Doppler sonar, speed log, etc.) when
leeward movement cannot be disregarded.
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 1, 2 or 3. They appear as TTs, each denoted with a small circle. When a plural number of
objects are selected, the mean value is used.
Note that this feature is not available when the AIS is active.
1. With the cursor inside the effective display area, spin the scrollwheel to display "Ref Mark" in the guidance area.
2. Select a small fixed island or any radar prominent point located at 0.1 to 24 nm from own ship.
3. Use the trackball to put the cursor (+) on the target selected at step 2.
4. Push the left button to enter the reference mark.
changes to in three minutes
R1
R1
Reference target
5. Repeat steps 2-4 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 Tot'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 "TT Lost REF Target" appears in the Alert Box. If all reference targets are lost, the speed indication
disappears. 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.
• 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/CRS page, referring to see section 2.5 How to Input Your Ship's Speed, and check Manual Speed or
Dual log as applicable.