Furuno FCR-2107 Operator's Manual page 370

16. Recording Functions
Position fixes defined by Line of Position (LOP)
A plotted line on which a vessel is located, determined by observation or measurement of the range or bearing to an
aid to navigation or other charted element. Two or more simultaneous observations can be combined to produce an
estimate of the ship's current position. If the position is based on only two observations, it is an "estimated position"
(EP); otherwise it is called a fix. Line of Position (LOP) can be found in the Sensors dialog, Record tab as one of the
Position Sources. A maximum of 6 observations can be entered to obtain a fix.
Basic operation: Coordinates of the aid to navigation can be entered into dialog boxes or they can be selected
graphically on the chart:
• S57, click on a charted object (beacon, light, buoy etc.). Description of the object appears above coordinate
boxes.
• ARCS: click anywhere in the chart.
Default values for bearing and range are approximated from ship's current position information. The time of
observation is stopped when the object is selected (or when Add button is clicked). Click Add button to include the
observation in the fix computation. The counter shows "new/1", and a second observation may be entered. The word
"new" indicates that the observation currently displayed is not yet included in the fix computation, and it appears as
a dashed line or ring on the chart. The added observations can be edited or deleted after selecting them in the
counter. When at least two measurements are entered, the EP or fix is computed and the coordinates are shown in
the top part of the dialog, and a position symbol appears on the chart. In the case of an EP, the letters EP are shown
on the right side of the coordinates. If a valid position estimate cannot be obtained, a message is displayed under the
coordinates. This may happen, for example, if the lines / circles have multiple crossings that are far apart, or if two
lines are nearly parallel or don't intersect at all. The accuracy limit (estimated standard error) is 1.0 NM. If the
estimate is valid, the Record button can be clicked to record the current position estimate in the voyage log.
Discrepancy between LOP result and ship position is also recorded in the log (this information may be viewed by
Info query on the position event symbol on the chart – which is displayed if position event display is on in chart
display settings). If dead reckoning is active, the button Use for DR is visible and clicking it will make the LOP
position a new starting point for DR.
Time transfer: If the observations are not simultaneous, they should be transferred to a common time. Transferring
is based on dead reckoning of ship movement. If a position line (or ring) is transferred, the letters TPL are shown
beside its timestamp on the chart. The method of transfer may be selected in the bottom of the dialog. Transfer to
latest transfers the measurements as if they were all made at the time of the newest measurement. Continuous
transfer transfers all measurements to real time. Transfer off can be used to check where the measurement origins
are. The position estimate and the record function follow the same logic, which means that Transfer off shows a
position that has no relevance and Transfer to latest sends an old position to the voyage log (timestamp in the log
does not match the position).
Timeouts: The observations cannot be used long after they were made because dead reckoning is inaccurate.
• One minute after the latest measurement it is labeled as a "DR" (dead reckoned position).
• The computed position times out in 5 minutes after the latest measurement
• An observation times out in 10 minutes, after which it disappears without any notice to the user
16-6