A simple question

[Carl C]

On a clear day, on average how far out must you venture to lose sight of shore due to the earths curve? (unable to see shore even with binocs)

[Morgan's Cloud]

It all depends on how high your eye is above sea level, but I think that for a person of averagel height the horizon appears only 2-3 miles away.
Of course the true answer to your question lies with knowing the height of the shoreline you refer to.
Out here the highest point of land is about 200' and the island dissapears from view when your out about 17 miles or so.

[Carl C]

Yes I knew it would change if there were cliffs or mountains on shore. Your answer is perfect. Thanks.

[Schnook]

I've always been told sea level to sea level straight line is about 3 miles. I'm thinking of stepping it off to see if it's true...:bonk:

[TuxedoPk]

Carl, Morgan and Schnook have hit it on the head. There are two components to consider: first the eye height of the observer above sea level (stand up or move higher on the boat to see further) and second the height above sea level of the object you are trying to view.

To give you an example of the distance differential based on the observers height, at 25' above sea level the viewable distance to the sea level horizon extends to over 6 miles. If I'm not mistaken the visual distance you can see is roughly 7% less than the distance radar can see an object.

*As an aside, if you're trying to determine the distance to an object (and don't have a radar arch in your classic), the Datascope I mentioned in another post will display it by just taking a bearing on the object. http://www.kvh.com/pdf/DS.Bro_2.01.pdf

[Carl C]

:cool!: :cool!: :cool!:

[goatee]

i thought it was 5 miles

[Carl C]

I think Morgan's Cloud seems right - about 3 miles if the shore is low and up to 17 miles if it is high. Close enough anyway.:lifeprese

[Ed Donnelly]

The earths curvature is 8" per mile, or 6' in 9 miles.
Now just calculate the height to eye level into the equation...Ed

[goatee]

ok,,,,
but what if it's low tide?







DOH!

[Carl C]

ok,,,,
but what if it's low tide?
DOH! No tide to worry about here!!!!!!!:)

[half shell]

17 miles.


Regards Bob

[TuxedoPk]

I'm having a problem reconciling these latest numbers being posted...

Ed- If I'm reading your post correctly you are suggesting that if an observer's eyes are at 6' above sea level they will be able to see an object on the horizon 9 miles away? That's like mini-me standing on a 22 classic. That distance seems really overstated.

Carl- 17 miles at low tide? Can you explain to me why you feel this is in the realm of accuracy? Maybe I'm missing something but I don't see how people are arriving at this number.

Are you referring to being able to see a tower on the shoreline at the horizon at that distance? If so, what difference does high tide or low tide make when you are viewing an object that is much higher anyway? For that matter, you can see objects over the horizon with significant enough height. My understanding was you were asking about the distance to an object at sea level based on the curvature of the earth.

[Ed Donnelly]

TuxedoPk; I called my buddy in Nova Scotia, retired head of the math dept. at Michael Power. He said it was quite simple,then started speaking some foreign language. All I could gather was,the radius of the earth is 3,963 miles,then using the Thorem of Pythagoras and using P with a tangent of 1 mile, it forms a triangle yada,yada,yada............Ed

[Carl C]

A simple question has gotten complicated! Morgan's cloud says his 200' island disappears at 17 miles. That's about the highest you'll find in Michigan so that answer is good enough for me. And it sounds like low shores start to disappear between 3-5 miles or maybe a little more. We don't have tides here to worry about. And lots of fresh water to drink if you get stranded! (and run out of beer)

[Cuda]

Standing in my fishboat, I'd lose sight of the condos at about 15 miles out in the gulf.

[Schnook]

I'm telling you guys, somebody step it off and tell me how far you had to walk to reach the horizon.

[Ed Donnelly]

Schnook; I have been walking for 61 yrs. Almost reached it.......Ed