Running fix (how to plot on the charts)

A Running Fix
A Definition
&
How to plot on a chart


What is a Running Fix?
• A “fix” is a common term used when the vessel’s position
can be confirmed by the intersection of two or more
position lines i.e. “fixing” the vessel’s position or, obtaining
a “fix”
• Position lines can be from celestial observations,
terrestrial bearings, terrestrial ranges, GPS co-ordinates,
etc
• A running fix is when we combine two position lines, which
are obtained at different times in order to obtain a fix
• To do so we must also know the ship’s course & speed


Question 1, Paper 1
• At 0930hrs in DR Lat 510 22’N, Long 0060 10’W an
observation of the sun gave a bearing of 0820(T) and an
Intercept of 0.8’ T
• The vessel is steering 3100 (T) at a speed of 8 knots
• At 1200hrs a Meridian Altitude of the Sun gave a Latitude of
510 37’N
• Find the vessel’s position at 1200 and also at 0930


Procedure
• Plot the given DR position

• Plot the given bearing, lay off the given Intercept and then plot
the position line
• Plot the vessel’s course from the ITP position
• Using the ship’s speed, calculate the distance run during the
time interval given (This calculation MUST be shown on your
answer book)
• Lay off the distance run on the plotted course.
• This will give the DR position for the time of the second
observation
• It is also the position through which we will transfer the first
position line.


Procedure
• Plot the first P/L through the second DR position. This will be a
“transferred” P/L
• Plot the second P/L or Latitude (whichever is given)
s
• Where the two P/L’ intersect this will be the “fix”


1200

DR
1200

DR
0930

Procedure
• Find the vessel’s postion at 0930 as follows
• To the fix at 1200hrs, lay of the vessels course and
distance steamed in the 2.5 hrs
• This will give the position through which to transfer
the observed noon latitude
• Where the transferred noon latitude intersects with
the morning position line will give the vessel’s position
for 0930


1200
DR
1200

0930

DR
0930