Finding your position with a chart and a compass.
This is the start of a sequence of lessons leading up to the level required to take a three point fix. A three point fix is simply the process of taking compass bearings of known landmarks, and plotting them on a navigation chart.
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At the time the bearings are taken you should take a note of the time, boat speed and the course being steered in the log book.
1st bearing: the Mast: 284°(M)
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 towards.
Check that you can positively identify these features visually before starting to take the fix.
The selected features are:
Obelisk (top left)
Mast (centre left)
Red port can buoy (bottom right)
Step 2: take the fixes and jot down the results.
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.
Step 3: Convert the magnetic bearings to true.
Variation 7° West.
Compass to true minus west.
Bearings:
Mast 284°(M) -7° = 277° (T)
Obelisk 309°(M) -7° = 302° (T)
Buoy 243°(M) -7° = 236° (T)
Plot the bearing lines on the chart
The time and log reading has been jotted down next to the fix.
The fix has created a small triangle called a cocked hat.
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