Cruisers Forum
 


Join CruisersForum Today

Reply
 
Thread Tools Rate Thread Display Modes
Old 31-07-2009, 16:42   #31
Registered User

Join Date: May 2008
Location: California's High Desert, Yucca Valley, CA
Boat: Ingrid 38 S/V Semper Fi
Posts: 83
I find two books to be really great. Please read great as easy to understand and use.

"One Day Celestial Navigation" Keeps it simple.

"The Complete On Board Celestial Navigator" Everything but the sextant. The current edition runs from 2007 to 2011. As I get back into using my sextant, I'm finding it a great guide to the subject.
__________________

__________________
04 Marine is offline   Reply With Quote
Old 31-07-2009, 17:09   #32
Registered User

Join Date: Jun 2009
Location: West Vancouver, BC, Canada
Posts: 195
Plastic is great

Quote:
Originally Posted by nautical62 View Post
I purchased one of the plastic ones years ago and learned to do noon sights but took it no farther. I'm mostly a coastal/islands cruiser so it was mostly just as a curiosity. My experience was the same as Dave on MaxingOut said. I could consistently get my latitude within a mile or so, but longitude was a different story all together.
These plastic models can get you home because they are easy to wash and clean; easy to adjust if they at least have two mirror screws. Don't grip them too hard, they will bend; relax now you are sailing.

If you can get your latitude within a mile, you can get your longitude within 2~10 miles by practicing running fixes; and by taking many sights, quickly, that you average. Getting too fussy about getting it right often doesn't work out at all well.

Then find your destination by deliberately aiming to one side by a good amount: 10 ~ 20 miles. When you see the beach turn towards your destination until you get there. Of course you are going to have to adapt that hint to your destination.
__________________

__________________
George Wade is offline   Reply With Quote
Old 31-07-2009, 23:52   #33
Registered User

Join Date: May 2008
Location: California's High Desert, Yucca Valley, CA
Boat: Ingrid 38 S/V Semper Fi
Posts: 83
Using a Sextant

It's been 30 years since I did any sailing. I had a plastic compass then and I have the same one now. Albeit, I just now getting back into sailing and using the sextant I find it rewarding at least then to locate yourself on the ocean using it.

As for the math, folks smarter than most of us have reduced that down to some pretty simple stuff. I would routinely take at least 3 sights and feel comfortable that I was inside of the results.

Although the math is a bit tricker, not much, you can use you sextant to determine how far you are from an object. Going off shore without one and some backup emergency navigation skills is asking for trouble.
__________________
04 Marine is offline   Reply With Quote
Old 01-08-2009, 03:36   #34
Senior Cruiser
 
Talbot's Avatar

Cruisers Forum Supporter

Join Date: Jun 2004
Location: Brighton, UK
Boat: Privilege 37
Posts: 3,579
Images: 32
Quote:
Originally Posted by 04 Marine View Post
Although the math is a bit tricker, not much, you can use you sextant to determine how far you are from an object. Going off shore without one and some backup emergency navigation skills is asking for trouble.
Or you could use Norries Tables and just look up the answer!
__________________
"Be wary of strong drink. It can make you shoot at tax collectors - and miss."
Robert A Heinlein
Talbot is offline   Reply With Quote
Old 01-08-2009, 09:06   #35
Moderator Emeritus
 
GordMay's Avatar

Join Date: Mar 2003
Location: Thunder Bay, Ontario - 48-29N x 89-20W
Boat: (Cruiser Living On Dirt)
Posts: 31,580
Images: 240
Not just for those seeking Certificates of Competency for Deck Officers and Marine Engineer Officers in the Merchant Navy, this site has lots of excellent information for cruisers, including navigational instruction:

Maritime and Coastguard Agency UK/EU ~ MCA Orals

Goto ➥
M.C.A. Oral Exam Information including a Massive Photo Gallery of Fishing and Merchant Navy Vessels
__________________
Gord May
"If you didn't have the time or money to do it right in the first place, when will you get the time/$ to fix it?"



GordMay is offline   Reply With Quote
Old 19-08-2009, 11:10   #36
Registered User

Join Date: Sep 2008
Boat: Bénéteau Oceanis 381 (38")
Posts: 3
The idea would be to preserve all practical methods, especially when they are fully independent. We once experienced full electrical power loss on a new boat (broken connector on alternator). The first line of defence was the handheld GPS, but we didn't have batteries for many uses (power-sucking little guy).
On the other hand, using tables in rough conditions may be a bit challenging (less than using the sextant, though), but is fully independent on electrical power.

So we keep the Sight Reduction Tables for Air Navigation aboard (just for cat. 1 regulations) and I try to practice sights (on my Freiberger, large) and then reduce them using the Nav4 Navigation Pac (additional module) by Thomas Metcalf on my slow but trusted HP-48G calculator (I added a body recognition program of my own devise) which runs on 4 easily duplicated AAA cells.
The whole kit (including note-taking bits) is protected by the sextant's (largish) box, see picture.

Precision is excellent (translate: at best 1/1000th that of a modern GPS, good enough at sea); be careful with the Moon, though (elevated horizon, by at least 5 minutes of arc, due to brightness of reflection). The most precise method (in my opinion) is crossed sights on 3 stars at dawn/dusk, because it doesn't depend on dead reckoning for translation of lines.
Attached Thumbnails
Click image for larger version

Name:	P1000548a.jpg
Views:	118
Size:	56.2 KB
ID:	9428  
__________________
Tramp is offline   Reply With Quote
Old 26-08-2009, 15:10   #37
Senior Cruiser

Cruisers Forum Supporter

Join Date: Aug 2009
Location: between the devil and the deep blue sea
Boat: a sailing boat
Posts: 17,314
I use it. Ocean passages. I check it against GPS about 2 times a week just to make sure I can do it if my GPS(s) pack up.

b.
__________________
barnakiel is offline   Reply With Quote
Old 26-08-2009, 15:18   #38
Registered User
 
Nauticatarcher's Avatar

Join Date: Jun 2007
Location: Mooloolaba, Qld
Boat: Islander Freeport 36
Posts: 396
If Captain Cook had had a GPS , which do you think he would have used?
__________________
Nauticatarcher is offline   Reply With Quote
Old 26-08-2009, 16:20   #39
Senior Cruiser
 
Cheechako's Avatar

Cruisers Forum Supporter

Join Date: Aug 2006
Location: Skagit City, WA
Posts: 19,363
at this point waste of time and money...
__________________
Cheechako is offline   Reply With Quote
Old 26-08-2009, 21:40   #40
Registered User

Join Date: Jun 2009
Location: West Vancouver, BC, Canada
Posts: 195
Quote:
Originally Posted by Nauticatarcher View Post
If Captain Cook had had a GPS , which do you think he would have used?
Both. He was a surveyor and navigator.
__________________
George Wade is offline   Reply With Quote
Old 27-08-2009, 10:49   #41
Registered User

Join Date: Jul 2008
Location: Boston, MA
Boat: Bristol 38.8
Posts: 1,625
It would be fun to learn celestial navigation and use a sextant. When I have the time, I just might. It's just geometry and a little trigonometry.

But for now, a backup handheld gps with plenty of spare lithium batteries in a waterproof case is my solution to losing electrical power in the boat. It's cheaper, too.
__________________
Curmudgeon is offline   Reply With Quote
Old 27-08-2009, 11:33   #42
Senior Cruiser
 
Cheechako's Avatar

Cruisers Forum Supporter

Join Date: Aug 2006
Location: Skagit City, WA
Posts: 19,363
I found it more frustrating than fun! But interesting anyway.... Pretty hard to develop a good technique of accurately matching the horizon on a boat even in fairly flat water. I'm sure 100's of attempts would help! Then there is the part of trying to adjust sails and look up all the crap in the books, time adjustments etc. Only to find out you screwed up somewhere! Gotta have a super accurate clock also.... right now my computer reads 1 min different than my blackberry!
__________________
Cheechako is offline   Reply With Quote
Old 27-08-2009, 12:45   #43
Senior Cruiser
 
Talbot's Avatar

Cruisers Forum Supporter

Join Date: Jun 2004
Location: Brighton, UK
Boat: Privilege 37
Posts: 3,579
Images: 32
Quote:
Originally Posted by Curmudgeon View Post
It's just geometry and a little trigonometry.
Not these days, using the air Nav tables and decent forms, it is just basic arithmetic. The only real skill is in the use of the sextant (and that is really experience more than anything else) and there is a little bit of skill in the plotting.

I have a set of forms which make this a relative doddle, and am happy to share whilst retaining the copyright. If you want them, send me a pm.
__________________
"Be wary of strong drink. It can make you shoot at tax collectors - and miss."
Robert A Heinlein
Talbot is offline   Reply With Quote
Old 27-08-2009, 12:48   #44
Senior Cruiser
 
Talbot's Avatar

Cruisers Forum Supporter

Join Date: Jun 2004
Location: Brighton, UK
Boat: Privilege 37
Posts: 3,579
Images: 32
Quote:
Originally Posted by Cheechako View Post
Gotta have a super accurate clock also.!
Slocum used an old tin clock which at one stage he boiled in water and then soaked in oil, so a pair of quartz watches should be sufficiently reliable to use as the chronometer. (keeping in a faraday cage of course!)
__________________
"Be wary of strong drink. It can make you shoot at tax collectors - and miss."
Robert A Heinlein
Talbot is offline   Reply With Quote
Old 27-08-2009, 14:46   #45
Senior Cruiser

Cruisers Forum Supporter

Join Date: Aug 2009
Location: between the devil and the deep blue sea
Boat: a sailing boat
Posts: 17,314
There seems to be a bit of 'urban legend' thing going on about the sextant, so:

- if Cook (but why just Cook?), if Cook (had) had GPS he would have used it, and probably he would have known (as he did) to use the sextant,

- using sextant / almanac IS easy - I can take the sight and calculate my LOP in about 10 minutes (a bit longer if no calculator available either), of course one has to spend some time&effort learning, but all sailing is learning no matter how much experience you already have, and yes - to me, it is fun,

- a single bad lightning bolt in your vicinity and you may end up with ZERO electronics, a single bad day for the US govt and they can switch off the GPS, - PLS read the most recent info on the state of GPS satellites and you will know why the 'new' Loran is being beefed up and introduced as backup,

I use the GPS a lot, and not just to get the fix. And I love and adore all the other things on board that blink and beep. But to me crossing an ocean without the sextant/almanac would be asking trouble. I understand that along the coast and for shorter passages sextant is not necessary (I never take mine out at such times anyway).

And finally, I hope I will make someone very angry when I state that I found most of those sailors who blah about the sextant being of no use next to ingnorant when it comes to proper use, terminology and limitations of the GPS too.

b.
__________________

__________________
barnakiel is offline   Reply With Quote
Reply

Tags
sextant

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
Inverted Sextant Scope clausont Navigation 5 24-05-2015 09:09
Sextant... blackjack Navigation 120 07-09-2013 09:16
Sextant charley Navigation 42 15-06-2011 17:39
Sextant for sail over40pirate Classifieds Archive 4 20-07-2008 03:50



Copyright 2002- Social Knowledge, LLC All Rights Reserved.

All times are GMT -7. The time now is 19:54.


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.