OUPV / Six Pack Captains License Course

PLOTTING - Triple Fix


Triple Fix

A “fix” is an accurate, known position.A “triple fix” is a method of plotting your vessel’s location by taking the bearings  from three fixed objects.  This is done by holding a hand-held magnetic compass and taking bearings from fixed objects that are found on a chart.  Objects that move with currents and tides should not be used for a triple fix.

Take the bearings from each of the three fixed objects and write them down.  Using the compass rose on your chart, and your parallel rulers and dividers, find each of the headings on the compass rose and walk the parallel rulers to the object the bearing was taken on.  Draw a line through the object out towards your position.  Repeat this procedure with the other two headings.   The point where all three lines come together represents your vessel’s position. Take the latitude and longitude of that point to find your position.  If the lines do not come together exactly, you will have a small triangle (not the Bermuda Triangle).  Place a point in the center of the triangle and take the latitude and longitude of that point.

Practical Exercise:
  Watch the demonstration video and use your chart and plotting equipment to solve the following triple fix problem.

You are in Long Island Sound in your vessel.  While holding a hand-held magnetic compass, you take bearings from three fixed objects as follows:

  • Bartlett Reef Light (Fl 5 sec., is 35 ft. high, 12 miles) bears 71 degrees magnetic
  • Plum Gut Light bears (Fl 2.5 sec., 5 miles, PA)  210 degrees magnetic
  • Little Gull Island Light bears (Fl, 91 feet, 18 miles) 140 degrees magnetic.

Based on these three hand held magnetic compass bearings what is your position?

The video will demonstrate how to plot the triple fix and take the latitude and longitude of that fix.  You can also use chart information or light list information to find the characteristics of lights found on charts.  (If no color is designated next to a light, the light is white.)  Remember that symbols on a chart can be found in the Nautical Chart No. 1 publication.