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Useful Tables Appendix I
USEFUL TABLES
Horizon Distance Based on Height of Eye
of the Observer(See Chapter 4, How to Determine When You Will Make Landfall)
Enter the table under the HE (Height of Eye) column with your height above sea level,
or the height of a charted object above sea level that has been corrected for tide. Read
the distance in nautical miles under the Horizon column.
You can also use the table to estimate the distance you will fi rst see an object of known
height, called geographic range. Th is does not take into account any element that reduces
visibility such as haze, fog, or precipitation.
For example, when standing on your fl ying bridge, your height of eye is 16 feet. You
are searching for a lighthouse with a charted height of 125 feet. At what distance might
you expect to sight the light on a clear night?
HE of 16 feet = 4.7 miles
HE of 125 feet = 13.1 miles
To find geographic range, add the two values: 4.7 + 13.1 = 17.8 miles
For safety, compare the geographic range to the nominal range shown on the chart
next to the light. Use the lower of the two ranges to estimate sighting. Or use the special
technique, described in the reference above.
For heights greater than the table shows, multiply the square root of the object height
by 1.17.