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Glossary of terms


How to Plot a Three Point Fix

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Not knowing where you are can easily happen at sea.
Knowing how to take a fix can give you a fresh starting point to plot your course home.

3rd bearing: Buoy 243° (M)
At the time the bearings are taken also note the time and the log reading.
Time: 1230 DST
Log reading: 28 Miles
To plot a three point fix you need to identify three points that you can see on the chart and at sea.
Ideally the three points should have a spread of at least 90 degrees but for this lesson we have reduced the angles to fit on the screen.
Step 1: Identify three charted features to take the bearings to.
The selected features are:
Obelisk (top left)
Mast (centre left)
Red port can buoy (bottom right)
Check that you can positively identify these features visually before starting to take the fix.
Step 2: take the fixes and jot down the results.
The fix has created a small triangle. If there are no dangers close by, choose the centre as the actual fix but be aware of the size of the error. If there are nearby dangers then choose a point in the triangle closest to the danger as the fix. This is the worst case scenario
Take the bearing closest to the heading (or stern) of the vessel first as this will change the least whilst you take the other two bearings.
Take a note of the bearings as you take them
1st bearing: the Mast: 284°(M)
2nd bearing: Obelisk 309° (M)
Step 3: Convert the magnetic bearings to true.
-7° W variation
(converting compass to true).
Bearings:
Mast 284°-7 = 277° (T)
Obelisk 309°-7 =302° (T)
Buoy 243°-7 = 236° (T)
Step 4: Record the time and log reading next to the fix on the chart.
Time: 1230 DST
Log: 28M