One point to add the John's answer to Greg:
If you want the distance at which a high object (such as a ship's mast)
can be seen while the ship itself is hull down, below the horizon, you
need to calculate the observer's horizon distance (using John's
equation) and add to it the horizon distance of the object being seen
(using the same equation but with the height of the mast, not the
observer's height of eye). Or, to simplify:
D (in miles) = 1.144 (root h + root h')
where h is the observers height of eye and h' is the height of the
object seen just dipping on the horizon, both measured in feet. For
those who prefer heights in metres, and assuming I haven't muddled the
math, the multiplier would be 2.075. (Distance still in nautical miles,
of course.)
Hardly needs Excel though. Any pocket calculator with a square-root key
will let you do that calculation in seconds.
Trevor Kenchington
John Broadwater wrote:
>
> Greg, the American Merchant Seaman's Manual (Cornell Maritime Press)
> has a table that gives the info. The table also gives the formula
> (taken from Am. Practical Navigator):
> D (n.mi.) = 1.144 [sqaure root] h , where h=height of observation
> point above sea level.
>
> From this, it would be easy to set up a simple Excel formula to do the
> job.
>
> John
>
> Greg Stemm wrote:
>
> > Does anyone know of a website that has a simple program that
> > computes the distance over the horizon that an item of a specific
> > height can be seen from shore from a specific height?Thanks,Greg
>
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