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Author Topic: How far can you see at sea?  (Read 4587 times)

Martin [Admin]

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How far can you see at sea?
« on: February 04, 2009, 06:34:27 pm »

Just looking around Google Earth at the estuary of the River Plate actually!
http://maps.live.com/default.aspx?v=2&FORM=LMLTCC&cp=-35.081708~-56.546631&style=h&lvl=9&tilt=-90&dir=0&alt=-1000&scene=7686220&phx=0&phy=0&phscl=1&encType=1

At sea level, how far can you see?

If I am 6Ft tall standing on the sea shore and I'm looking at another bloke (who is also 6ft tall), how far apart can
we be and still see each other, before the curvature of the Earth get in the way?

( Taking for granted it's a clear day and I'm using a good binoculars or a telescope. )
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Ghost in the shell

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Re: How far can you see at sea?
« Reply #1 on: February 04, 2009, 06:35:27 pm »

around 23 miles, from calais you can see dovers cliffs
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Roger in France

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Re: How far can you see at sea?
« Reply #2 on: February 04, 2009, 06:40:50 pm »

.....or the other bloke sinks!

Roger in France
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Colin Bishop

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Re: How far can you see at sea?
« Reply #3 on: February 04, 2009, 06:42:16 pm »

It's quite a bit less than that in Martin's example. See the table on this link: http://www.caronia2.info/gloss03.php#vis

Colin


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wideawake

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Re: How far can you see at sea?
« Reply #4 on: February 04, 2009, 06:47:33 pm »

or

http://www.wikihow.com/Calculate-the-Distance-to-the-Horizon  includes a good diagram of the method

Seeing Calais cliffs from Dover assumes you're standing on top of the Dover cliffs.

Guy

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nhp651

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Re: How far can you see at sea?
« Reply #5 on: February 04, 2009, 06:54:45 pm »

the answer to martin's question, using his measurements is actually much shorter than you think. baring in mind that a 6' figure is only a symbol, and you would not be decernable other than a dot, the actual distance is 13.23 miles.
how do i know.
it was one of the questions that we used to set kids as a trigonometry question in maths for years. :-))
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Martin [Admin]

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Re: How far can you see at sea?
« Reply #6 on: February 04, 2009, 06:58:08 pm »

It's quite a bit less than that in Martin's example. See the table on this link: http://www.caronia2.info/gloss03.php#vis

Colin

I've seen that chart Colin... how come we can see France on a clear day?
( Assuming the height of the cliffs at Dover are 100Ft high. )
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Colin Bishop

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Re: How far can you see at sea?
« Reply #7 on: February 04, 2009, 07:02:16 pm »

Martin, the cliffs at Dover are around 300 feet high or more, the cliffs on the French side are as high if not higher so if you use Guy's calculator....

And the Brits and Germans used to shoot at each other during the war - or more often at the convoys transiting the Dover strait.

Colin
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dreadnought72

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Re: How far can you see at sea?
« Reply #8 on: February 04, 2009, 08:42:40 pm »

Of course, if you're on Mars, the situation is different.

I wrote this some time ago.

Very useful for seeing how far Spirit, the MER rover, on top of Husband Hill, could see across the crater of Gusev...  %%

Andy, who needs to get out more.
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dreadnought72

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Re: How far can you see at sea?
« Reply #9 on: February 04, 2009, 08:52:35 pm »

I really need to get out more. I'm replying to myself now.

I've just had a delve into the tools at that URL, and this one, which does conversions between various units, on a drag 'n' drop basis, is quite useful. One of my bookmarks!

Andy
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Peter Fitness

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Re: How far can you see at sea?
« Reply #10 on: February 04, 2009, 10:02:28 pm »

Very useful, Andy. I've now bookmarked it too.

Peter.
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BobF

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Re: How far can you see at sea?
« Reply #11 on: February 05, 2009, 12:54:09 pm »

I was told that a  person six feet tall, eyes slightly lower of course, can see four and a half miles to the horizon.
I live at Bridlington and walk to the beach every morning with my Springer (dog)  If the shipping is well out, although I can see it from the promenade, most of the ships are gone when I get down on the beach, which I would think is about twenty feet lower. I am referring to hull and superstructure.

When I was learning marine navigation, there was a question asking why the light house set back from the cliff edge was visible on the outward journey but not visible on the return trip six hours later, even though we were the same distance out from the shore.
Any one not know why? PM me for the answer,
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tigertiger

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Re: How far can you see at sea?
« Reply #12 on: February 05, 2009, 01:21:13 pm »

Tide gone out?
Outward journey in dark hours?
Raining on the way home?
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polaris

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Re: How far can you see at sea?
« Reply #13 on: February 05, 2009, 01:23:01 pm »


Dear All,

At this moment I can tell you it's apx. 250 metres!!! {:-{

Regards, Bernard
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Bryan Young

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Re: How far can you see at sea?
« Reply #14 on: February 05, 2009, 03:26:36 pm »

Tide gone out?
Outward journey in dark hours?
Raining on the way home?

Good answer tiger! Remind me of the tidal range at Springs at Bridlington?
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BobF

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Re: How far can you see at sea?
« Reply #15 on: February 05, 2009, 06:51:52 pm »

Just under seven meters
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Bunkerbarge

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Re: How far can you see at sea?
« Reply #16 on: February 05, 2009, 11:23:15 pm »

North Atlantic, Mid Winter, 12,000 ton container ship, you can see as far as the next wave!!
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Bryan Young

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Re: How far can you see at sea?
« Reply #17 on: February 06, 2009, 05:13:17 pm »

Bunkerbarge, if we are going down that route:- many times transitting the Bay of Biscay (and the W.Coast of the USA) ships less than 2 miles away in a cross swell would be totally invisible when both were in a trough. A bit out of kilter and the "one on top" would look quite threatening to the "one on the bottom". Looked very odd when both were "on top" at the same time! BY.
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maninthestreet

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Re: How far can you see at sea?
« Reply #18 on: February 06, 2009, 09:50:05 pm »

Well, on a clear night, you can probably see  2.5 million light-years if you look upwards and see the Andromeda nebula.
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Martin [Admin]

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Re: How far can you see at sea?
« Reply #19 on: February 07, 2009, 03:47:38 am »

 {-)
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Martin [Admin]

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Re: How far can you see at sea?
« Reply #20 on: February 07, 2009, 03:48:52 am »

Tide gone out?
Outward journey in dark hours?
Raining on the way home?

What was the correct answer BobF?
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Captain Jack

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Re: How far can you see at sea?
« Reply #21 on: February 07, 2009, 08:10:27 am »

While learning coastal navigating tricks for dead reckoning voyages, we were taught how to judge our distance from land by looking at the dwellings on shore. If you could discern the seperate windows on a house, what is your range to the beach?
 Just a bit of a trivia question here for the "saltiest of sea dogs" among us....
(assuming the house is at, or near the shoreline, of course)
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malcolmfrary

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Re: How far can you see at sea?
« Reply #22 on: February 07, 2009, 12:03:02 pm »

Discerning windows is a bit subjective and depends on eyesight and size of window.  When I finally had an eye test and got my windows I paid a visit to an office which was on the top floor of the Blackpool Post Office building.  There was a good view of the Bleasdale fells from there - about 20-ish miles.  Without the glasses I could see the hills, and have an indication that houses were there.  With the glasses on, I could see that the houses had upstairs and downstairs windows.
I was told that sitting in a rowing boat, your horizon was three miles away, presumably you would be seeing another person sitting in another rowing boat from the waterline up.
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Tug

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Re: How far can you see at sea?
« Reply #23 on: February 09, 2009, 11:22:54 am »

OK I remember this bit
If you are standing on the deck of a ship/boat say 15 feet asl and you can see the waves breaking on the beach then you are two and a half miles away, maximum. (you could of course be a dam sight closer...
since then we have global warming and metrication?    >:-o

"Why do people pay  to go up tall buildings and then put money in  binoculars to look at things on the  ground?" 
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Captain Jack

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Re: How far can you see at sea?
« Reply #24 on: February 09, 2009, 03:02:17 pm »

OK I remember this bit
If you are standing on the deck of a ship/boat say 15 feet asl and you can see the waves breaking on the beach then you are two and a half miles away, maximum. (you could of course be a dam sight closer...
since then we have global warming and metrication?    >:-o

"Why do people pay  to go up tall buildings and then put money in  binoculars to look at things on the  ground?" 

Bravo Zulu, shipmate.
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