How to "Read" a Lighthouse on a Nautical Chart
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Around 1:28, you say, "... nominal range, does not take into account the curvature of the earth." If so, how is it computed?
A quick bit of trig shows that treating the earth as a sphere of radius 20,925,524.9 feet gives a distance of 11.116 nm for the nominal range of a light 109 feet tall, so I would suspect that the curvature of the earth is exactly what they're using. (R * arcsec((H+R)/R))
One question: the height of a fixed light the height above chart datum? Above MLLW? Or what?
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Keep up the good work. Most of this info I know and some of it I have forgotten and some of it is new. Thanks again.
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Wow, definitely important to know. Thanks!
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Nominal range is based on candlepower of the light in clear visibility. You may or may not see a light at its nominal range. The earth’s curvature often limits the distance you will sight a light because of your height and the light’s height(charted at MHHW) above sea level.
Use this formula (1.17 X square root of the light’s height). In this case, powerful Sand Key could be seen at 12.2 miles. A less powerful light such as Loggerhead Key (151 feet at 20M) would be seen at just 14.4 miles.
seasensical 6 months ago