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02-04-2016, 15:08
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#1
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Registered User
Join Date: Feb 2014
Location: Palm Coast Florida
Boat: 2018 Seadoo GTX 230
Posts: 1,059
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Google tells me line of sight
With Google there really is not much that one can not find out. But none the less of is hard to believe you can only see 2 - 3 miles.
For some reason without trees/ mountains in your way I would have thought the line of site on the ocean would be 25 -30 miles. Not 2 - 3 miles.
Does that surprise anyone else?
Sent from my SM-G360V using Cruisers Sailing Forum mobile app
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02-04-2016, 15:47
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#3
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Registered User
Join Date: Mar 2008
Location: Huron, Ohio
Boat: Albin Coronado 35(1972)
Posts: 640
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Re: Google tells me line of sight
most definately, pigs on a beach 5 miles away might appear to be flying ...
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02-04-2016, 16:16
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#4
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Moderator Emeritus
Join Date: Aug 2005
Location: Carlsbad, CA
Boat: 1976 Sabre 28-2
Posts: 7,505
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Re: Google tells me line of sight
You can see more than 3 miles but the horizon is only about 3 miles away because of the curvature of the earth. If something is off the water like a mast, airplane or ships superstructure, it can be seen from quite a distance away. Saw the Big Island when closing Hawaii at about 30 miles but that was because of clouds and haze over the Island. Probably could have seen it at 50 miles since it sticks 13,000 feet in the air if visibility would have been better.
__________________
Peter O.
'Ae'a, Pearson 35
'Ms American Pie', Sabre 28 Mark II
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02-04-2016, 16:26
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#5
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Registered User
Join Date: Aug 2013
Location: Back in Montt.
Boat: Westerly Sealord
Posts: 8,194
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Re: Google tells me line of sight
Line of sight on the ocean and elsewhere on a cloudless day is quite a few light years away.
However the horizon , if your height of eye is about 2 metres, is about 3 miles.. i.e. you would be able to see a beach ball floating on the horizon...given 20/20 vision and a pair of 10 x 50 Fujinons.
If there was someone else looking at the beach ball from 3 miles away on the other side , that is 6 miles from you, you would be able to see his hat.
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02-04-2016, 20:51
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#6
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Registered User
Join Date: Mar 2008
Location: Calgary, AB, Canada
Posts: 6,252
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Re: Google tells me line of sight
The formula:
1.17 times the square root of your height of eye above the water in feet = Distance to the horizon in nautical miles
__________________
CRYA Yachtmaster Ocean Instructor Evaluator, Sail
IYT Yachtmaster Coastal Instructor
As I sail, I praise God, and care not. (Luke Foxe)
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03-04-2016, 05:27
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#7
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Registered User
Join Date: Apr 2013
Posts: 11,002
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Re: Google tells me line of sight
I think the confusing part is you are thinking of objects that extend above the waters surface. Those can be seen from much further away (depending on the object height)
The google example is the actual water surface visibility (presumably assuming no waves).
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03-04-2016, 06:10
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#8
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Registered User
Join Date: Feb 2014
Location: Palm Coast Florida
Boat: 2018 Seadoo GTX 230
Posts: 1,059
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Re: Google tells me line of sight
No...not thinking I am at water level but stating up on the deck of a 30' boat. Probably 3 feet above the water. Eyes 8' above the water. Google tells me I can see approx. 3 miles.
I like the formula that was supplied in a previous post.
Now I am trying to back into the curvature of the earth with math. Just to double check. Using circumfirance of the earth as 24,901 statute (I think) miles.
Any math majors out there?
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03-04-2016, 06:19
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#9
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Registered User
Join Date: Jan 2011
Location: Cowichan Bay, BC (Maple Bay Marina)
Posts: 9,706
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Re: Google tells me line of sight
Quote:
Originally Posted by tuffr2
Any math majors out there?
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You're reinventing the wheel (pun intended ).
In addition to the handy formula previously provided, any qualified reference text on nautical navigation will include this information and show you the derivation.
__________________
Stu Jackson
Catalina 34 #224 (1986) C34IA Secretary
Cowichan Bay, BC, SR/FK, M25, Rocna 10 (22#) (NZ model)
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03-04-2016, 06:23
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#10
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Registered User
Join Date: Mar 2008
Location: Calgary, AB, Canada
Posts: 6,252
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Re: Google tells me line of sight
Quote:
Originally Posted by valhalla360
I think the confusing part is you are thinking of objects that extend above the waters surface. Those can be seen from much further away (depending on the object height)
The google example is the actual water surface visibility (presumably assuming no waves).
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Use the forumla twice, once for your height, once for the height of the object at which you are looking, add the two together.
Or use this nomogram
__________________
CRYA Yachtmaster Ocean Instructor Evaluator, Sail
IYT Yachtmaster Coastal Instructor
As I sail, I praise God, and care not. (Luke Foxe)
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03-04-2016, 06:35
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#11
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Registered User
Join Date: Feb 2014
Location: Palm Coast Florida
Boat: 2018 Seadoo GTX 230
Posts: 1,059
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Re: Google tells me line of sight
All this started when my friend asked...how far away is that mountain. I said 30 statute miles. Then at the ocean someone asked how far away is that sailboat. I said I do not know...thus my Google search.
Now I am surprised to know you can only see a few miles on the water because of the curvature of the earth. Kinda neat stuff to know.
Sent from my SM-G360V using Cruisers Sailing Forum mobile app
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03-04-2016, 06:41
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#12
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Registered User
Join Date: Jan 2011
Location: Cowichan Bay, BC (Maple Bay Marina)
Posts: 9,706
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Re: Google tells me line of sight
Quote:
Originally Posted by tuffr2
Now I am surprised to know you can only see a few miles on the water because of the curvature of the earth. Kinda neat stuff to know.
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WAIT!!! It's NOT flat???
Where'd all those submarines go???
__________________
Stu Jackson
Catalina 34 #224 (1986) C34IA Secretary
Cowichan Bay, BC, SR/FK, M25, Rocna 10 (22#) (NZ model)
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03-04-2016, 07:04
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#13
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Registered User
Join Date: Apr 2013
Posts: 11,002
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Re: Google tells me line of sight
Quote:
Originally Posted by tuffr2
All this started when my friend asked...how far away is that mountain. I said 30 statute miles. Then at the ocean someone asked how far away is that sailboat. I said I do not know...thus my Google search.
Now I am surprised to know you can only see a few miles on the water because of the curvature of the earth. Kinda neat stuff to know.
Sent from my SM-G360V using Cruisers Sailing Forum mobile app
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This is exactly the situation I and a few others have described. The mountain and the sailboat both extend well above the surface of the earth and thus can be seen for much further than the actual surface of the water.
Thought experiment (ignoring curvature of the earth): Find a 5' fence and place a tennis ball and a lawn chair 5' on the far side of the fence. Now slowly back up until you lose sight of the ball. Then back up until you lose sight of the chair.
Assuming you are fairly tall and have a 6' eye height you will lose sight of the ball at just over 6' 3" from the ball (1'3" from the fence).
Assuming the chair is 4' tall, you won't lose sight of it until you are 10' from the chair.
The curvature of the earth makes the math a little more complex but the concept is the same.
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03-04-2016, 07:18
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#14
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cruiser
Join Date: Aug 2015
Location: Charleston, SC
Boat: 53' Hatteras Cruising Yacht
Posts: 175
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Re: Google tells me line of sight
Use a drone
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03-04-2016, 07:32
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#15
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Registered User
Join Date: Mar 2009
Location: Homer, AK is my home port
Boat: Skookum 53'
Posts: 4,042
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Re: Google tells me line of sight
A publication named after Nathaniel Bowditch has many wonderful tables that can help with many questions that a mariner might have while at sea, think of it as google of the maritime book world.
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" Wisdom; is your reward for surviving your mistakes"
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