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Old 16 August 2002, 13:11   #1
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How far can you see?

A multiple choice thread, this, for anyone who went to school and was awake during maths.
1). On a perfect day, from the helm of your RIB, how far can you see before the earths curvature obscures your view of your fellow ribster?
2). If you climbed up your yacht's mast (the one you keep back at the Marina and don't tell anyone on this Forum about), to 10m. How far can you see then?
3). I ask because a) I am an anorak and b) because my house is 100m exactly above sea level with views across Torbay. Out of idle interest, while sipping my G&T on the verandah, I wondered how far I could possibly see.
There is a formula, isn't there?
Anyone bright spark know what it is?
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Old 16 August 2002, 13:43   #2
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According to Barbra Streisand...

"On a clear day, you can see forever"...
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Old 16 August 2002, 14:03   #3
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Yers..thank you Neil. I just knew the US contingent would be able to offer SOMETHING useful to this highly technical discussion.
I actually ask the question to cover the embarrasment of my wife saying to me "Brian, how far away do you think that ship is on the horizon over there?"
And me having to answer "Erm, paralax, Darling, earths curvature and all that malarky..Oh look, my glass is empty, must get a refill". In the hope that when I get back she will have forgotten all about it. Trouble is she is going to insist on an answer one day and she thinks I'm quite bright. Don't want to disillusion her just yet.
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Old 16 August 2002, 14:07   #4
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What yer need to do Brian is fit a Radar scanner on the roof then you can look respond to Christines question with "23nm its steering 090 at 24kts and its CPA is 18miles"!!!
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Old 16 August 2002, 17:09   #5
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I was always led to believe that one can see approximately 25 statute miles?!
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Old 16 August 2002, 18:56   #6
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Brian,

From page 37 of the current Macmillan Reeds:

Ht of eye of 1.5m = horizon of 2.5M
Ht of eye of 100m = horizon of 29.4M

Of course these are dependant on the quantity of G&T's consummed and whether you are horizontal or vertical at the time of sight; ht of tide; viz, etc etc

Peter (anorak-in-waiting)
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Old 19 August 2002, 05:27   #7
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It also depends on where u are I work on the bridge of a ship and due to refraction and other phenomena have seen land that is 40-60 miles away.....
But generally on a clear day...20ish miles from the ship's bridge and in a RIB about....5-8 miles.....

alex
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Old 19 August 2002, 17:23   #8
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Why worry about it? if you are there you are, if not you're not. Sometimes it is better to have poor visability, this way you do not have that longing of "are we nearly there"when you hit the harbour wall!

A piece of really good news is Allen C from the Isle of Man is back in circulation so watch out when he starts posting items on this site
The best answer when the wife / girlfriend ask's how far is lie about it!
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Old 02 September 2002, 05:05   #9
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Hi folks

Here is an interesting link on Boaters World Wide Browser:

http://www3.ns.sympatico.ca/leeh/default.htm

There are all sorts of useful calculators, including one to find the distance of the horizon. Put it in your favourites list. You need to scroll down the main page a bit and look in the box on the right.

Keith (web surfer extraordinaire) Hart
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Old 02 September 2002, 05:26   #10
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Nice one Keith.
I especially like the geographic calculator.
Many is the time when we have been chugging along and said to ourselves "first one to see The Eddystone gets a free beer-should be just off our port bow". Now I know that if the Eddystone is x metres high, Wont be able to see it until I am y miles away. Bloody useful that.
To take Alan's point. Alan I find I get soooo bored that just about anything gets my interest as a point of discussion. Counting down the miles, can I see xyz headland, I wonder what that yacht bears from us, how does MARPA work, what the nearest port, what do you reckon the current is running at, ANYTHING !!!
For example, I pose the following:
I want to calculate how busy a motorway is from a fixed point, this is usually measured in number of vehicles per hour passing said point. Well, if the motorway is mega-choker then the number of vehicles PASSING the fixed point drops to a low number, doesnt it? So the motorway isn't very busy then is it? But we all know it's choker. So how do they do it.
Usually shuts the crew up for a bit whilst their brains slowly unfreeze!
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