Cruisers Forum
 


Join CruisersForum Today

Reply
 
Thread Tools Rate Thread Display Modes
Old 03-04-2016, 09:46   #16
Registered User
 
wrwakefield's Avatar

Join Date: Feb 2011
Location: Wrangell Island, Alaska
Boat: Nauticat 43
Posts: 861
Re: Google tells me line of sight

Quote:
Originally Posted by tuffr2 View Post
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
This is an example of the things we don't always think about... and you now have your answer.

For example, I had some friends sailing with me for a few days years ago in Prince William Sound [ocean waters...] and they were both engineers.

One afternoon, while enjoying the 5000+ foot mountains surrounding the fjord we were in, one casually asked me what our altitude was. I looked over at them with my best deadpan face waiting for the punch line, but it was not forthcoming. Seizing the opportunity, I grabbed the tide tables, did a quick rule-of-twelfths calculation in my head, and replied seventeen feet; give-or-take.

She immediately blushed. We all had a good laugh, and then I answered the intended question: The mountains with the rounded tops are under 5000 ft because that was the height of the ice in this region during the last ice age... Those with jagged tops are over 5k ft...

Regarding the horizon, I tell guests to just assume their eyeballs are 9 ft above the water, and take the square root of that for a close enough estimate. There is your 3 miles to the horizon... [Another reason to use AIS at sea; to avoid the other moving parts...]

Cheers!

Bill
__________________

__________________
SV Denali Rose

Short on opinions; focused on research, facts & experience [yours and ours...]
wrwakefield is offline   Reply With Quote
Old 03-04-2016, 10:10   #17
Registered User

Join Date: Feb 2014
Posts: 994
Re: Google tells me line of sight

Lol...yep, engineers ask these type of questions. I have a friend that is a civil engineer. Lots of distance and elevation gain/decrease questions.

Standing at a beach looking out over the ocean is 2 miles and at an elevation of 9' is 3 miles. I think I know something he may not know...



Sent from my SM-G360V using Cruisers Sailing Forum mobile app
__________________

__________________
tuffr2 is offline   Reply With Quote
Old 03-04-2016, 11:25   #18
Registered User
 
Cadence's Avatar

Join Date: Dec 2008
Location: SC
Boat: None,build the one shown of glass, had many from 6' to 48'.
Posts: 6,058
Re: Google tells me line of sight

Quote:
Originally Posted by boatman61 View Post
If you look at the horizon very carefully on a good visibility day you'll maybe notice an ever so slight curve either edge of your vision.. one of the reasons from a 9ft eye elevation one can almost exactly calculate a ships distance.. as soon as you make out the waterline its 3 miles away and closing... 20/20 vision only..
When you can make out the waterline, a ship is to damn close.
__________________
Cadence is offline   Reply With Quote
Old 03-04-2016, 12:06   #19
Registered User

Join Date: Feb 2008
Location: GREEN COVE SPRINGS, Florida
Boat: Irwin 43 Mk111 CC, Sloop
Posts: 362
Send a message via Skype™ to adlib2
Re: Google tells me line of sight

Quote:
Originally Posted by tuffr2 View Post
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
From cockpit height (6ft) the horizon is 3 miles due to earths curvature and sand on the beach becomes visible at 1 mile.
__________________
adlib2 is offline   Reply With Quote
Old 03-04-2016, 12:18   #20
Registered User
 
Cadence's Avatar

Join Date: Dec 2008
Location: SC
Boat: None,build the one shown of glass, had many from 6' to 48'.
Posts: 6,058
Re: Google tells me line of sight

? On the crest or in the trough.
__________________
Cadence is offline   Reply With Quote
Old 03-04-2016, 16:36   #21
Registered User
 
captmikem's Avatar

Join Date: Mar 2014
Location: Ft Lauderdale
Boat: KP 46
Posts: 317
Images: 2
Re: Google tells me line of sight

Bowditch, table 12
Attached Thumbnails
Click image for larger version

Name:	12.JPG
Views:	68
Size:	258.7 KB
ID:	121955  
__________________
captmikem is offline   Reply With Quote
Old 03-04-2016, 16:45   #22
Registered User
 
captmikem's Avatar

Join Date: Mar 2014
Location: Ft Lauderdale
Boat: KP 46
Posts: 317
Images: 2
Re: Google tells me line of sight

try that again, for some reason it did table 13, which can be used but takes a bit.

Here is table 12
Attached Thumbnails
Click image for larger version

Name:	12a.JPG
Views:	65
Size:	118.8 KB
ID:	121957  
__________________
captmikem is offline   Reply With Quote
Old 03-04-2016, 21:48   #23
Registered User

Join Date: Feb 2016
Posts: 125
Re: Google tells me line of sight

Quote:
Originally Posted by wrwakefield View Post
This is an example of the things we don't always think about... and you now have your answer.

For example, I had some friends sailing with me for a few days years ago in Prince William Sound [ocean waters...] and they were both engineers.

One afternoon, while enjoying the 5000+ foot mountains surrounding the fjord we were in, one casually asked me what our altitude was. I looked over at them with my best deadpan face waiting for the punch line, but it was not forthcoming. Seizing the opportunity, I grabbed the tide tables, did a quick rule-of-twelfths calculation in my head, and replied seventeen feet; give-or-take.

She immediately blushed. We all had a good laugh, and then I answered the intended question: The mountains with the rounded tops are under 5000 ft because that was the height of the ice in this region during the last ice age... Those with jagged tops are over 5k ft...

Regarding the horizon, I tell guests to just assume their eyeballs are 9 ft above the water, and take the square root of that for a close enough estimate. There is your 3 miles to the horizon... [Another reason to use AIS at sea; to avoid the other moving parts...]

Cheers!

Bill
If engineers were on the peak of the mountain and boiled water for their cup of tea it would boiled at 95 degrees Celsius.

Cheers.
__________________
peter57 is offline   Reply With Quote
Old 04-04-2016, 01:47   #24
Registered User
 
HankOnthewater's Avatar

Join Date: Dec 2012
Location: West Australia
Boat: production yacht, suitable for deep blue water ;)
Posts: 308
Re: Google tells me line of sight

Quote:
Originally Posted by jackdale View Post
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
For those thinking in metres, the formula is:
2.1 x sqrt (of height of eyes) + 2.1 x sqrt (of height of object)
height of eyes and height of object is in metres above sea level
the calculation will give visibility in NM.
"sqrt" means square root

I have attached an older excel spread sheet I made many years ago; this calculates all the distances, but I am sure googling will give you a calculator on the net somewhere...........
hmmmm just looking now:
How to Calculate the Distance to the Horizon - BoatSafe.com
And if one wants to get technical:
Distance to the Horizon
Attached Files
File Type: xls LIGHTS_DIPPING.XLS (44.5 KB, 8 views)
__________________
Wishing you all sunny skies above, clear water below, gentle winds behind and a safe port ahead,
and when coming this way check http://www.cruiserswiki.org/wiki/Albany,_Australia
HankOnthewater is offline   Reply With Quote
Old 04-04-2016, 08:46   #25
Registered User
 
Juho's Avatar

Join Date: Apr 2015
Location: Finland
Boat: Nauticat 32
Posts: 716
Re: Google tells me line of sight

I have used these formulas also for estimating the distance to seamarks. If you know the approximate height of a seamark, and you can see e.g. half of that seamark above the horizon, you can estimate the distance to it. You need to know your own distance to the horizon and the distance of the "below the horizon part of the seamark" to the horizon, and then reduce the latter from the former (to get the distance between you and the seamark).

Usually plotters are much better in estimating the distance and will quickly tell you all the distances. I never bother to make these calculations while at sea. But I have calculated some rule of thumb values (knowing the usual height of my eyes in the boat, and being able to estimate the height of horizon at some common seamark models). These values can be helpful especially when using binoculars (that make it otherwise more difficult to guess the distance).
__________________
Juho is offline   Reply With Quote
Old 04-04-2016, 09:05   #26
Senior Cruiser
 
jackdale's Avatar

Cruisers Forum Supporter

Join Date: Mar 2008
Location: Calgary, AB, Canada
Posts: 5,040
Images: 1
Re: Google tells me line of sight

BTW - if you are determining the distance to land based object, such as a light station, you must account the state of the tide at the time you are determining the distance. Elevations are based on HHWLT. That really complicates matters.
__________________
ISPA Yachtmaster Ocean Instructor Evaluator
Sail Canada Advanced Cruising Instructor
IYT Yachtmaster Coastal Instructor
ASA 201, 203,204, 205, 206, 214
As I sail, I praise God, and care not. (Luke Foxe)
jackdale is offline   Reply With Quote
Old 04-04-2016, 09:06   #27
Registered User
 
deblen's Avatar

Join Date: Oct 2014
Location: Grand Manan,N.B.,Canada N44.40 W66.50
Boat: Mascot 28 pilothouse motorsailer 28ft
Posts: 1,400
Images: 1
Re: Google tells me line of sight

I would like to add Marine Radar to discussion. FYI
Radar & eyesight can see "beyond" the horizon,if atmospheric conditions are just right-clear visibility & a water vapor layer. It is called "Looming" & is similar to mirage.
https://en.wikipedia.org/wiki/Loomin...tion_phenomena
However,when conditions are "normal"-ie: when you really need your radar-two avg 40ft boats do well to see each other at 4-5NM.

Radar Horizon Calculator
__________________

__________________
My personal experience & humble opinions-feel free to ignore both
deblen is offline   Reply With Quote
Reply

Tags
google

Thread Tools
Display Modes Rate This Thread
Rate This Thread:

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off


Similar Threads
Thread Thread Starter Forum Replies Last Post
Wind tells seaturkey Monohull Sailboats 7 01-07-2014 08:05
Turkey Blocks Google Earth & Google Maps MarkJ Europe & Mediterranean 7 04-07-2010 13:30
VHF line-of-sight or not Hal Marine Electronics 7 23-01-2009 07:09
fuel line sight glass gettinthere Engines and Propulsion Systems 3 25-11-2008 11:16



Copyright 2002- Social Knowledge, LLC All Rights Reserved.

All times are GMT -7. The time now is 20:00.


Google+
Powered by vBulletin® Version 3.8.8 Beta 1
Copyright ©2000 - 2017, vBulletin Solutions, Inc.
Social Knowledge Networks
Powered by vBulletin® Version 3.8.8 Beta 1
Copyright ©2000 - 2017, vBulletin Solutions, Inc.

ShowCase vBulletin Plugins by Drive Thru Online, Inc.