Distance Off by Horizon Angle

It is possible that you want to know your distance off a light, a headland or a buoy but do not know its height and so cannot use a vertical sextant angle. There is one other method that may work. Measure the angle between its waterline and the horizon. This is called distance off by horizon angle (see Figure 12.8).

Three points to note: firstly, if your height of eye is in feet then your answer is in feet; secondly, this is one of the rare occasions when the correction for dip is added to your reading; thirdly, working in small angles pushes home-made sextants to, and probably beyond, the limits of their accuracy. Do not expect too much.

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