Entering Own Ship's Speed; Echo-Referenced Speed Input - Furuno FCR-2107 Series Operator's Manual

4.4

Entering Own 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 Entering Own 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 which can measure ship's leeward movement (Doppler sonar, speed log, etc.) when
leeward movement can not 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 tracked targets, 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 0.2 to 24 nm from own ship.
3. Use the trackball to place the cursor (+) on the target selected at step 2.
4. Push the left button to enter the reference mark.
changes to
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 "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).
•
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/Cse menu, referring to see section 2.5 Entering Own Ship's Speed, and check Manual Speed or Dual
log as applicable.
in three minutes
R1
4. Tracked Target (TT) Operation
4-3