NavList:

A properly made hand bearing compass will not exhibit deviation but will suffer from variation. However the boat you are on will have potential deviation which is a function of the orientation of the boat, i.e. course not bearing. If you maintain course while taking a number of bearings then the deviation will be constant. If the bearings are corrected for variation and deviation then they can be directly plotted and the intersection will be a fix.

By taking the difference between bearings and calling that a horizontal angle the perhaps unknown deviation and unaccounted for variation are eliminated but now you must plot a circle through the pairs of points and where they intersect becomes a fix.

Use straight edge and compass to erect perpendicular bisector to pair of points.
Use protractor to establish base angles at the marks equal to angle between the points. Extend them to find the center of your circle and then draw the circles for various pairs. No calculations other than differenc of bearings are required.

The fix is independent of variation and deviation.

Dave fleming
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