What are methods of getting Ship Position if GPS fails at mid sea?

Bearing and Sounding

This method may be used providing :

• Allowance is made to reduce the sounding to chart datum.
• The depth contours are well defined.
• The contour in question only crosses the position line in one possible place.
• The depth contour crosses the position line at a wide angle

Running Fix

Under some circumstances, such as low visibility, only one line of position can be obtained at a time. In this event, a line of position obtained at an earlier time may be advanced to the time of the later LOP. These two LOPs should not be parallel to each other; remember that the optimal angular spread is 90°. The position obtained is termed a running fix because the ship has “run” a certain distance during the time interval between the two LOPs.

It is more commonly used when only one object is available for bearings and there is no means of measuring the range. In this case there is a planned delay between bearings so that the change in bearing will provide an acceptable angle of cut.