Raymarine GPS navigation User Manual

Page 63

arrival at the waypoint, the ships’ L/L must match WPT L/L. If the ship’s
displayed L/L is ASF corrected, the

memory must have corrected

L/L coordinates if you are to arrive at the same location again. The NAV 398

takes care of this automatically for you.

If you see some difference between the waypoint’s L/L in memory and the

ship’s position at the

location, we suggest that you save the

as an Event, while sitting next to the mark. This will put a corrected

position into the

memory and will permit the repeatable accuracy

of loran

50 feet) to guide you to the same location the very next time.

Auto ASF

Normally the ASF program is set to Automatic when the 508/A sensor

leaves the factory. However you should check the POSITION CORR. menu
and verify that the program is ON at the first opportunity. On the Main Menu

Directory, press

the menu verify that the

ASF correction is highlighted at AUTO. Pressing the

steps the

selections

AUTO to

to OFF, etc.

Manual TD Corrections

Although adding TD correction values to correct

your

position is not a common practice,

there are times when

of a fixed landmark are

available. It is fairly easy to correct your
reading using TD difference values. The procedure
for making manual TD corrections appear in the

following example:

Example: The actual TD readings given on a chart

for a sea buoy are

and

The

loran display reads

for S 1 and

for S2 while sitting next to the buoy.

13900.7 Chart

25590.0 Chart

-13899.5 TD readout

25590.2 TD readout

1.2 correction

-0.2 S2 correction

LORAN

O F F

o . o u s

o.ous

N 00.00’

w 00.00’

AVERAGING

LORAN

After subtraction, the values

for

and

for S2 were obtained

and can now be entered manually for the ASF values. To enter these values,

select the

POSITION CORR

Press the

ASFCORRECTION

highlight

MANU

and press

T D w i l l b e h i g h l i g h t e d t o

indicate numeric values should now be entered.

OPERATION 3-50