Cruisers Forum
 


Join CruisersForum Today

Reply
 
Thread Tools Rate Thread Display Modes
Old 05-04-2014, 15:51   #1
Registered User

Join Date: Aug 2010
Location: sydney, australia
Boat: 38 roberts ketch
Posts: 1,021
Images: 3
The Importance Of The Noon Sight?

I've often read about the religious consistency of early mariners in catching the noon sight and never really thought too much about why because i've never thought of trying celestial nav without an almanac but, seeing as a pretty good fix on latitude is relatively easy just by measuring to the pole position using the southern cross or the polestar, having a simple way to get a rough longitude fix using the noon sight and a watch ought also to be reasonably simple.
If you have a sextant and a watch set to GMT you should be able to calculate your longitude from a midday sunsight - although given the difficulty of determining the precise time of the highest angle, it might be hard to be very accurate. But it ought to be possible to within a few miles which would be better than nothing.
Is that why the noon sight was particularly important?
__________________

__________________
charliehows is offline   Reply With Quote
Old 05-04-2014, 16:39   #2
Moderator
 
cabo_sailor's Avatar

Cruisers Forum Supporter

Join Date: Mar 2008
Location: Tarpon Springs FL
Boat: Cabo Rico 38
Posts: 1,905
Re: The Importance Of The Noon Sight?

Because the British Navy used it to determine the new day which determined when the rum or spirits were issued?

It's also the easiest sight to take.

Rich
__________________

__________________
cabo_sailor is offline   Reply With Quote
Old 05-04-2014, 16:51   #3
Senior Cruiser
 
StuM's Avatar

Cruisers Forum Supporter

Join Date: Nov 2013
Location: Port Moresby,Papua New Guinea
Boat: FP Belize Maestro 43
Posts: 6,713
Re: The Importance Of The Noon Sight?

The noon sight is the only one that lets you determine your position (both Lat and Lon) with a single sight.
__________________
StuM is online now   Reply With Quote
Old 05-04-2014, 16:55   #4
Registered User
 
capt-couillon's Avatar

Join Date: Mar 2013
Location: Onboard (Boot Key Harbor)
Boat: Cornado 25
Posts: 494
Re: The Importance Of The Noon Sight?

Finding latitude from a noon sight is the simplest celestial nav calculation there is and yields very accurate results. No timepiece required, only a nautical almanac. Latitude is much trickier from a noon sight needing an accurate timepiece and a steady hand. Hardest for me is to determine actual "high noon" The sun always seems to hang at its highest (or meridian) altitude each day for a couple of minutes or so, and to time noon precisely you need to figure out exactly when the middle of that “hang time” is. Have to stay in practice with the sextant every day.

After a week or so, I can usually get within a couple miles of latitude and within 10 to 12 miles of longitude. Not accurate in these days of GPS, but in a pinch I can always "run down my latitude" and even if I don't make the harbor entrance, at least I shouldn't miss the island.
__________________
"It seemed like a good idea at the time"
capt-couillon is offline   Reply With Quote
Old 05-04-2014, 17:22   #5
Registered User
 
Randy's Avatar

Join Date: Oct 2008
Location: San Diego
Boat: Searunner 31
Posts: 639
Re: The Importance Of The Noon Sight?

The calculation for lat is simple but diddling around waiting for the sun to reach its zenith then start to fall...the value isn't there for me. I don't have the patience. A standard sight reduction at approx local apparent noon will create a nearly east-west lop in less time.
__________________
Randy is offline   Reply With Quote
Old 05-04-2014, 17:28   #6
Registered User
 
Randy's Avatar

Join Date: Oct 2008
Location: San Diego
Boat: Searunner 31
Posts: 639
Re: The Importance Of The Noon Sight?

Though if you want, take a series of shots at 2 - 3 min intervals 10 min before your precalculated time of meridian passage continuing for 10 min past. Chart a bell curve of the sights and that will create your true LAN.
__________________
Randy is offline   Reply With Quote
Old 05-04-2014, 19:58   #7
Registered User
 
Orion Jim's Avatar

Join Date: Dec 2008
Location: Noank, Ct. USA
Boat: Cape Dory 31
Posts: 1,075
Images: 6
Re: The Importance Of The Noon Sight?

Just learned to plot the "bell curve" last week in a celestial navigation course. Never heard of it before this introduction. Using the sextant allows you to fully appreciate our early navigators. They were very skilled and intelligent seafarers.
__________________
Orion Jim is offline   Reply With Quote
Old 05-04-2014, 21:23   #8
Registered User

Join Date: May 2008
Location: daytona beach florida
Boat: csy 37
Posts: 2,844
Images: 1
Re: The Importance Of The Noon Sight?

what randy says. take a series of shots before and after lan and then extrapolate lan.

another method i've heard of is to take a shot a few minutes before lan. don't change the settings on the sextant. then begin taking shots after lan - without changing the settings on the sextant - until the sun returns to the sextant angle. lan is then exactly (?) between the two shots.

lot's easier than a running fix but requires the sun to be visible for a few minutes around lan and being on deck in the hot sun.

as for the ancient mariners being so careful to take the noon sight, back in those days that's all they had was the noon sight. without a timepiece they couldn't determine longitude. but the noon sight did give them latitude. and because of that, to this very day, a ships daily progress is always calculated from noon to noon, and not calendar days.
__________________
onestepcsy37 is offline   Reply With Quote
Old 05-04-2014, 21:26   #9
Senior Cruiser
 
SkiprJohn's Avatar

Cruisers Forum Supporter

Join Date: May 2006
Location: Kea'au, Big Island, Hawaii
Boat: Cascade, Sloop, 42 - "Casual"
Posts: 14,192
Re: The Importance Of The Noon Sight?

Quote:
Originally Posted by Jim Walsh View Post
Just learned to plot the "bell curve" last week in a celestial navigation course. Never heard of it before this introduction. Using the sextant allows you to fully appreciate our early navigators. They were very skilled and intelligent seafarers.
You betcha! Pretty interesting reading about the evolution of navigation. Until there was an accurate time piece onboard it was pretty rough trying to determine where your longitude was. More or less dead reckoning. Determining latitude wasn't too hard but still required a bit of skill so folks would sail down or up to their latitude then head for their destinatione along that latitude. Called "Sailing the Latitudes."
__________________
John
SkiprJohn is offline   Reply With Quote
Old 05-04-2014, 22:39   #10
Marine Service Provider

Join Date: Sep 2012
Location: Annapolis aka sailing capital of the world
Posts: 525
Re: The Importance Of The Noon Sight?

Art Birney wrote a terrific and brief and simple book on Noon Sight Navigation and Dava Sobel's "Longitude" details the historical account of John Harrison's clocks which finally won him the Admiralty Prize and can be seen in Greenwich--a worthwhile trip I was lucky to do. With the bell curve as described above, I found it helpful to wear my watch face up (opposite side of "normal" wear) as I make adjustments on the sextant. I did all this years ago before cellphones and gps and all on a plastic Davis sextant...and with help from an rdf to fix lines and get WWV. Nice to know folks are still doing this. The beauty of sextants in this high tech age is it requires you to keep a log. And all you really need for the noonsight.....is the sun!
__________________
Paul Annapolis is offline   Reply With Quote
Old 11-04-2014, 22:31   #11
Registered User

Join Date: Aug 2010
Location: sydney, australia
Boat: 38 roberts ketch
Posts: 1,021
Images: 3
Re: The Importance Of The Noon Sight?

yeah, thats how i learned to do sights - usually try to get at least 6 and then average them, only difference is in calculating the bell curve.
__________________
charliehows is offline   Reply With Quote
Old 13-04-2014, 03:26   #12
Registered User
 
El Pinguino's Avatar

Join Date: Aug 2013
Location: Punta Arenas ahorra
Boat: 39' Westerly Sealord
Posts: 3,952
Re: The Importance Of The Noon Sight?

Quote:
Originally Posted by charliehows View Post
Is that why the noon sight was particularly important?
Was a (long ) time when that was all they had.

I've just been reading Basil Ringrose's 'South Sea Waggoner' (again).

A bit of background - Bartholemew Sharp and some likely lads including young Bazza crossed the Isthmus in 1680, nicked a couple of Spanish ships and wrought havoc on the Pacific coast of south America for a couple of years.

That done they left an anchorage on Duke of York Island in 50*37'S... pottered off down and around the Horn ( going down to 58*23'S and becoming the first englishmen to go eastabout round the Horn).

About 2 months later they reached the latitude of Barbados... hung a left.. and made landfall ten days later.... 3 months and 9000 miles without sight of land.

Not a bad bit of work with no clock, a couple of astrolabes and possibly a cross-staff, and just their reckoning of their 'eastings' and 'westings'.
El Pinguino is offline   Reply With Quote
Old 13-04-2014, 03:36   #13
Nearly an old salt
 
goboatingnow's Avatar

Cruisers Forum Supporter

Join Date: Jun 2009
Posts: 13,649
Images: 3
Re: The Importance Of The Noon Sight?

Quote:
Originally Posted by Randy View Post
The calculation for lat is simple but diddling around waiting for the sun to reach its zenith then start to fall...the value isn't there for me. I don't have the patience. A standard sight reduction at approx local apparent noon will create a nearly east-west lop in less time.

Absolutely. With the motion of a small boat. Bell curves to calculate zenith are a search for precision not accuracy.

Dave


Sent from my iPad using Tapatalk
__________________
Check out my new blog on smart boat technology, networking and gadgets for the connected sailor! - http://smartboats.tumblr.com
goboatingnow is offline   Reply With Quote
Old 13-04-2014, 03:53   #14
Registered User
 
El Pinguino's Avatar

Join Date: Aug 2013
Location: Punta Arenas ahorra
Boat: 39' Westerly Sealord
Posts: 3,952
Re: The Importance Of The Noon Sight?

Three other probs.... if you are in high lats the sun is going to 'hang' for a long time .... if your lat and the sun's dec are about equal its going to go from an easterly to a westerly azimuth very very quickly and its not easy on a big ship to get a mer alt when the alt is greater than 85* never mind a yacht.
If you are keeping time well removed from actuality the sun may be on the meridian well into your afternoon. Chile f'rinstance keeps double summer time for much of the year... sun not on merid until about 1400 local. Cuts into Piscosour time and the afternoon nap...

Best daily navigation solution as far as I am concerned is a sight when the sun is either right ahead or right astern... gives you an accurate run.... and another when the sun is on the beam.. lets you know if you are left or right of track.

Back to OP... yes mainly tradition even 50 years ago.... running down to Capetown ex UK we would stay on GMT ( or BST) until a few nights before Capetown. Midday position ( ie 1200 ship's time) was simply a morning sight run up to another sight at 1200.

The 2nd mate would take a mer-alt in the middle of his watch just to fill in his afternoon....
El Pinguino is offline   Reply With Quote
Old 13-04-2014, 03:55   #15
Nearly an old salt
 
goboatingnow's Avatar

Cruisers Forum Supporter

Join Date: Jun 2009
Posts: 13,649
Images: 3
Re: The Importance Of The Noon Sight?

Personally I prefer star sights., proper fix

Dave


Sent from my iPad using Tapatalk
__________________

__________________
Check out my new blog on smart boat technology, networking and gadgets for the connected sailor! - http://smartboats.tumblr.com
goboatingnow is offline   Reply With Quote
Reply

Tags
import

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
Noonsite Posting - Importance of Ditchbag avb3 Health, Safety & Related Gear 0 21-05-2011 10:11
Importance of Boat Shelter Freerider Construction, Maintenance & Refit 2 18-04-2011 10:21
The Importance of Going Cruising NOW! oldsalt_1942 The Sailor's Confessional 49 30-12-2008 07:32
Importance of a Cat's center clearance capcook Multihull Sailboats 17 15-11-2008 11:15



Copyright 2002- Social Knowledge, LLC All Rights Reserved.

All times are GMT -7. The time now is 23:54.


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.