Well Greg me ol' matey,

'Ave ye forgott'n th' ol' 'pirate rule o' thumb'?

Stand affor the main mast; move parrot from shoulder to fist; extend arm
towards feature 'n' align tip o' beak with top o' feature, then measure
inches down thy parrot's leg to the horizon.  Multiply by ten gives the
number of leagues off.

Some do say it be rough and ready me hearties, but it is guaranteed to put
ye in th' shot park area.

Martin

(NB, On leave this week and shore happy)

Martin Dean
Director
Archaeological Diving Unit
University of St Andrews
Fife
KY16 9DA

01334 462919 office
01334 462921 fax
07836 226 346 mobile

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www.adu.org.uk

-----Original Message-----
From: Investigating the environment of marine archaeological sites
[mailto:[log in to unmask]]On Behalf Of Trevor Kenchington
Sent: 23 April 2001 16:36
To: [log in to unmask]
Subject: Re: Distance Computation

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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>

--
Trevor J. Kenchington PhD                         [log in to unmask]
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