SailNet Community

SailNet Community (http://www.sailnet.com/forums/)
-   General Discussion (sailing related) (http://www.sailnet.com/forums/general-discussion-sailing-related/)
-   -   Celestial Navigation (http://www.sailnet.com/forums/general-discussion-sailing-related/71327-celestial-navigation.html)

Slayer 01-14-2011 12:07 PM

Celestial Navigation
 
This was touched on in the thread below, but rather than hijack that thread I decided to start a new one.

I know little to nothing about celestial navigation, but it seems very complicated and difficult to learn. If you do ocean crossings is it necessary or important to know? Do you have to be well versed in it to benefit from it, or can it still be usefull with some knowledge of it?

I did an overnight sail and used stars for my bearings for periods of the sail, mostly for steering when I grew tired of checking the gps. So it was helpful to me for that limited use. Are there any recomended books or videos to start learning with?

Hesper 01-14-2011 02:21 PM

It's not as bad as it seems - at least not with the right instructor. I passed the Power Squadron's Junior Navigator course (basic celestial) and even if I never use it, it was worth it. I've never looked at the sky quite the same way since. And yes, even the basic is a good back-up for an ocean crossing for when your GPS batteries get wet.

I tried the advanced course twice, but the conceptual trigonometry was just too much for me. Maybe I'll try again when I get older and wiser. I don't know about videos, but there are plenty of good books. Just hang around a bookstore (not a website) and you'll see.

AdamLein 01-14-2011 02:46 PM

It's not necessary, but the prudent mariner etc.

I think the more important question is, do you want to learn it? If not, you can get away without it. If so, it's a lot of fun. However there are a million threads on this site that give pointers to how to get started; I recommend using google to search.

SailingIsis 01-14-2011 05:01 PM

These days I think there is very little case to be made that celestial navigation is necessary or prudent. (I think the prudent mariner should have a backup GPS unit)

That is: assuming that the GPS system (NAVSTAR) does not go down for an extended period of time - and even then there are GLONASS and GALILEO systems as backup.

Electronics on board of course can fail, but at the current price of handheld units, having several back-ups is no longer an issue (be sure to put one in your ditch bag or even in your life raft). These will be battery powered and of course it's possible the whole electrical systems fails, but a baggy of batteries will allow you a fix a couple times a day for months.

That being said, there is a charm and a certain sense of accomplishment to do it the old fashioned way. It can get quite complicated, but some of the basics like a noon shot are certainly not too hard for anyone to master.

Omatako 01-14-2011 05:10 PM

The bottom line is that if you want to have a full understanding about how the whole celestial thing works mathematically then you have a task ahead of you.

However, if you can grasp the fundamentals about taking a sight, filling in a basic form, using a plotting sheet and looking up data in manuals, the physics of getting a fix are not difficult to master.

Forms and plotting sheets have been posted on this board several times and a search should locate them. If not, I can help with some, PM me if you wish.

My advice is take a basic course on celestial which will help you understand the terminology and process but don't try to master all the (as others have rightly called it) conceptual trig and other mathematics that go with it. I would advise against trying to learn from a book.

Libellula 01-14-2011 05:24 PM

really a very simple answer
Buy a cheap sextant and learn how to take a noon shot
you will be amazed at how simple it is
by doing this then you will begin to see that there are instances when only you can save your bacon
this will also require that you keep up with where you are and how fast you are travelling (DR)
and two GPSs do not work if there is a failure of the system
when one takes off into the ocean be prepared to take care of yourself

Omatako 01-14-2011 05:32 PM

Quote:

Originally Posted by Libellula (Post 686945)
and two GPSs do not work if there is a failure of the system

Are there still people who believe that the GPS system is going to go down? A hundred or more satellites would simultaneously have to fall out of the sky for the system to fail.

How long does something have to keep flawlessly working before it is universally trusted?

People die due to aircraft falling out of the sky at a rate of a million to one compared to those dying due to GPS "failure" yet we all still trust commercial airlines but not GPS.

Go figure.

Let's face it, celestial navigation is a recreational pastime.

btrayfors 01-14-2011 05:52 PM

GPS system failure is a distant possibility, excepting the potential for localized jamming or the USG deciding to once-again implement "selective availability".

However, the possibility of onboard GPS units failing is much greater. Power failures, battery depletion, unit malfunctions, and EMF due to nearby or direct lightning strikes are much more a possibility.

Celestial is a good backup, and it's very good exercise for the brain. I agree that one needn't "master" the spherical trigonometry involved. The noon sight is very easy to learn. So, too, is the noon sight for longitude, which involves taking equal altitude sights before and after meridian passage. Learn these, and if you're interested and so inclined, continue on from there.

Not sure about the plastic sextants. I like good equipment. Good sextants cost a bit, but they're worth it. Get a good used Plath or Tamaya or Freiburger or Simex or Aires sextant. For heaven's sake, don't waste your money on any of the many "replicas" available on the market....they are strictly for show, not serious use.

Bill

Boasun 01-14-2011 05:55 PM

Quote:

Originally Posted by Omatako (Post 686950)
Are there still people who believe that the GPS system is going to go down? A hundred or more satellites would simultaneously have to fall out of the sky for the system to fail.

The satellites will not be falling out of the sky, they are 11000 miles above the earth. But a major solar flare, a large dither put back in by the military, or jamming by those are enemies or those who think of it is a practical joke. Certain electronic equipement have jammed ship board GPS's.
Plus you may have not plugged in the correct chart datum. Or position the GPS antenna in the optimum position on your vessel. Bad antenna connection have caused one cruise ship to run aground. And I've had three GPS's go belly up on me, which is a good reason to have all of your way points listed in your Navigation work book AND use secondary means of Navigation to confirm your position.:cool:

Omatako 01-14-2011 06:06 PM

Quote:

Originally Posted by Boasun (Post 686958)
And I've had three GPS's go belly up on me,

That's uncommon bad luck. The hand-held that I use has been functioning perfectly for several years and the others that I have bought for redundancy are still in their original packaging.

Yes, I hear the possibilities of solar flares and the like but it would be interesting hear, maybe in the form of a poll, how many people have been unable to get GPS position for more than an hour or so due to issues not on their own boats.

I personally have never had such an event anywhere I've been in the world so I'm noticeably skeptical.


All times are GMT -4. The time now is 07:03 PM.

Powered by vBulletin® Version 3.8.7
Copyright ©2000 - 2014, vBulletin Solutions, Inc.
SEO by vBSEO 3.6.1
(c) Marine.com LLC 2000-2012