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Argos2020 12-28-2001 12:26 PM

Celestial Navigation
 
Where can I learn to do Celestial Navigation? I consider this a must for
transoceanic passage.

Don''t trust the GPS 100%, been lost before with it. Handy Compass helped me out of a bind many a time.

Thanks

Jeff_H 12-28-2001 03:17 PM

Celestial Navigation
 
I originally learned celestial navigation from a text book that I picked up at a second hand store. It was designed to work with a standard set of step by step forms. It was a time consuming process to reduce a sight. Today there are easier methods and specially designed calculators that make reducing a sight much easier and there seems to be reasonably clearly written texts out there. I looked at one at Barnes and Noble not that long ago.

There also are schools and videos on the subject. School of Ocean Sailing offers live-aboard celestial navigation courses. www.sailingschool.com

You can download a short guide to Celesial Navigation at: http://home.t-online.de/home/h.umland/page2.htm

Some local Power Squadrons will periodically run a celestial navigation course.

One thing I found with Celestial Navigation is that it is strictly use it of loose it. I have not done anything with celectial navigation in over 20 years and doubt that I could take a good sight or reduce a sight without a lot of struggling.

Regards
Jeff

sailaway21 10-01-2006 03:25 PM

Celestial Navigation essentials
 
I am a master mariner, oceans, with quite a bit of experience at celestial navigation. I even taught it, between stints at sea, at the USMMA. My recommendations for you are different than they'd be for a prospective third mate. He/She must understand all of the theory, different methods of sight reduction, as well as fun facts to know and tell about the moon. You just want to find out where you're at. The first thing you need, of course, is a sextant. This is not an area to scrimp. Don't bother with cheap plastic models. Get a good used Tamaya or Plath. Plath will run you more for the name. I have a Tamaya and it's a fine instrument. Either one's cost new will make your hair hurt. Where ever you get one, make it's purchase conditional on your checking it out. If it has been dropped, and bent, you've got a nice lampshade base. Bowditch, vol 1, will tell you how to check it out and adjust your mirrors. Make sure that all of the sun and horizon shades are present.If the mirrors are corroded they can be resilvered. You want this level of sextant for a couple of reasons. The first is accuracy. Why buy something that is inaccurate, or worse yet, inconsistant, when that's the whole purpose one getting one in the first place. The other reason is that these instruments are alot weightier than the cheaper "yachting" versions. You want that weight because you are going to be out in the wind, braced against your cabin or mast trying to line up a little pinprick of light with a perhaps fuzzy horizon. It's much easier to do with a heavier instrument. When I went from a light weight, well used training instrument to a heavier one my results improved greatly. One possible source for a good used instrument might be the Int. Organization of Masters, Mates, and Pilots. They are based out of Linthicum Heights, Maryland and have union halls in all major ports. They can give you the tel. nos. for some of their halls and you could post a wanted notice. You have a better chance of getting an instrument in good condition from someone who has made his living with it than you do from someone to whom it has only been a part of a nautical motif in their bar. Purchasing, by any method, should be contingent on evaluation of the instument. Just buy Bowditch, vols 1 & 2, you need them anyway. You won't find instructions on cel nav per se there but you will find everything else a competent navigator should know. Every deep water sailor worth his salt has them, no merchant ship leaves port without them, and the sections on hurricanes and the biography of Nathaniel Bowditch are worth the price of admission alone. Next you need an accurate chronometer. This is much easier than in times past due to the advances in clock technology. Regardless of the Rolex ads, I do not recomend a wrist watch. Get a good piece, with a sweep second hand, and Lithium batteries. A good chronometer is not necessarily one that doesn't lose a second over a year but one that is consistent. On a ship, the chronometers are wound at the same time every day, a radio "time tick" taken, and the results logged. That logbook goes with the chronometer into the lifeboat, on a really bad day for all concerned, and is used to adjust the chronometers reading based on it's rate of error. Most have a pretty steady rate, ie. a second every two days, etc... You can check yours off your GPS or some other reliable source-even a radio time tick if you have a HF receiver. Sounds just like the start of a BBC broadcast on NPR! Check your chronometer for a month, at the same time each day, and you'll have a pretty good idea of it's gain or loss. Also, do this again anytime you replace the batteries or as the batteries age. Accurate time is the key to celestial navigation, in particular longitude, and no effective cel nav was possible except a rudimentary determination of latitude be fore a good chronometer was invented. Treat your chronometer like your sextant, both should have a high quality carrying case, well padded. You'll also need a stopwatch. With it you will shoot your celestial body, click it, go to your chronometer, click again, noting the exact time and jot down your sight. Then go and shoot your next star. You do not have to become versed in the uses of h.o. 229 or other sight reduction tables, although I do recomend the purchase of the nautical almanac. (pub by DMHC and HM Hydrological Office jointly) I have a Tamaya navigation calculator and it will do the sight reduction for you, lickety split.. After shooting stars we used to have half an hour to fortyfive minutes reducing our sights to LOPs in the chart room using 229 and that's for an experienced mate. The navig. computer will do great circles, etc for you as well. That's about it from an equipment standpoint. As Jeff alluded to there are alot of texts out on learning cel nav, I think Dutton's is as good as any and, since it's been published since
christ was a coxswain you should be able to find one used and cheap. It will tell you how to construct plotting sheets which you'll use offshore, but will probably want to make for learning purposes. Your biggest need now will be a horizon. You need a clear view of the horizon to shoot stars, sun, moon, and planets. Ashore, practically speaking, this means you'll only have less than 360 degrees to utilize. Not to worry, you can start out shooting the sun, coming back each hour to shoot it again and, after 2 or 3 sights you'll have a fix. Depending on time of year, you may be able to shoot Venus at the same time. I do not recc. the moon. It will do in a pinch, but it's too fast moving for good LOPs (line of position). Practise in the wind, rain, cloudy, overcast-pretty much all conditions-to hone your skills. It's alot more "fun" on a moving deck. Ashore you should be able to get three or four LOPs that pretty much "pinwheel". Remember, this is how all electronic navigation systems are evaluated for accuracy. Thet get five guys with sextants over on some seaside cliff in Ireland and start shooting stars. When they compare results that's where they are and the error is in the GPS, loran, etc...We've been watching the movements of the heavens since Noah dropped us off the boat (lost his masters ticket, and rumor has it, is holding forth in Snug Harbor on the merits of riding out hurricanes stern to) ane we've had a real good idea of their positions the last few hundred. As a matter of practise, you will want to precompute your shots. Pick half a dozen bodies to shoot and figure their altitude and azimuth. Write those down on some foolscap and go out on deck. You may have only seconds to grab a sight through an opening in the clouds. You precompute using your DR position. Also remember that two good sights are better than five sloppy ones. I jot down "good", "exc", "so-so", eyc... for mine. When plotting, weigh their validity based on that. The end result of this is that you'll know exactly where you're at. In this age of electronics it is far too easy, and far too common, to rely on some black box. Loran C, in the southern Gulf of Alaska, would put you five miles east or west of your DR track for about twelve hours steaming and then have you right back on track. No problem, plenty of sea room, etc... but signal strength was the same, it would happen day or night, voyage after voyage, and the only way you knew that it was off was by celestial navigation. The Transit satellite navigation system needed a fairly accurate estimate of SMG (speed made good) to get a good fix. Remember, you are the master of your vessel and while you may not have ten million dollars worth of cargo on board, you probably have something of equal or greater value at risk. And you're already in your lifeboat. You're having a bad day, your batteries shorted ou and everthing electronic is on the fritz, you go out get a shot of Polaris and Arcturus, plot it and there you are. We know where we are now lets go sew uo that torn jib. And you'll sleep that night!

camaraderie 10-01-2006 04:39 PM

"Remember, this is how all electronic navigation systems are evaluated for accuracy. Thet get five guys with sextants over on some seaside cliff in Ireland and start shooting stars. When they compare results that's where they are and the error is in the GPS, loran, etc"

That is complete BS!
http://www.kowoma.de/en/gps/errors.htm details error sources for GPS and how they are calculated....and 10 meters is about accuracy today...not the 2 miles for a GOOD clestial shot.
Yah...thats why the Navy stopped teaching it! It is so accurate ....NOT. I don't know where you came from capn' but your chronometer has a few cukoos in it!

hellosailor 10-01-2006 04:51 PM

Worse, using sextants and other optical instruments AT OR NEAR A COASTLINE is going to introduce further errors and inaccuracies caused mainly by the changing temperature of the air (which means a changing and unknown index of refraction) in those areas where the sea/land temperature is causing the air temperature to vary relatively widely.

The land may not be rocking, but the air at the coastline makes it just as "unstable" as a small boat rocking at sea.

sailaway21 10-01-2006 06:12 PM

Cel Nav
 
Navigation has been a "collateral" duty for an officer in the navy for at least the last thirty years. That's hardly a condemnation of celestial navigation-more an indictment of the navy. Where's Harry Weems when you need him? Two mile accuracy is adequate for any off-shore navigation system and, in fact, that is the standard. If you need greater accuracy you are probably in a piloting situation. And I would not classify two miles as a good observation in good conditions. With a cheap sextant or poor conditions, ie... rolling deck underfoot, not bad, but I wouldn't consider it my best effort. Refraction is a zero sum game with a marine sextant as horizon and sky glass experience the same and cancell. A bubble sextant is different and those correction factors are included in the air navigation tables. The colregs require decision-making not be done based on scanty information, especially scanty radar information. I,m sure that you've heard of radar assisted collisions. The important point being that the prudent navigator is required to utilize all means of navigation (that's why the radar is on even in perfect visibility) and you do not know there is an error in an electronic instrument unless you compare it to some other reference. All of the maritime academies still teach celestial navigation and the USCG still tests it for licensing (90% is passing grade) and that's why shipowners entrust 150 million dollar ships to them. Use every tool you have, but don't tell me that GPS has eliminated the need for celestial navigation. But then, some people don't see the need for paper charts either!

sailingdog 10-01-2006 06:16 PM

One other thing... Tayama and Plath make beautiful instruments, but are four times the price of a Astra IIB, which is a pretty decent, if relatively inexpensive sextant. About $500 retail, less if on sale. The plastic ones can be problematic as they can warp if left in the sun, and the warping is often not very noticeable but will throw your readings way off. Tania Aebi, of Varuna fame, had that problem.

The sextant handbook is a very good book on how to adjust and calibrate a sextant for side error, index error, etc.

Lots of good books on sextant use out there too. Blewitt's Celestial navigation for Yatchsmen is an old fallback. The Complete Celestial Navigator is another good one.

camaraderie 10-01-2006 08:42 PM

"But then, some people don't see the need for paper charts either!"

Yeah...like the US Navy again!

As the Institute of Navigation stated in 1999:
With the advent of GPS and other high-performance electronic satellite navigation systems that are fast and inexpensive, require no operator effort, and give a continuous read-out of position to within a few meters, using a sextant to take the stars is surely obsolete. Perhaps the death knell for celestial navigation was sounded in May 1998 when the United States Naval Academy announced it was discontinuing a course on celestial navigation and the use of the sextant that has been taught since the Academy's founding in 1845. Sooner or later, air and nautical almanacs will no longer be published and there will no longer be a need for hand-held instruments for taking the stars." Somewhat sadly, this may mean the demise of art in navigation.
************

If you do celestial as a pleasure and an art...more power to you. If you think of it as an essential skill for a navigator today...you are a curmudgeon with your shorts in a knot!

http://www.ion.org/newsletter/v8n4.html

erps 10-01-2006 10:15 PM

I have a bit of a knot in my shorts. I learned celestial from a book by Bruce Paulk using a cheap $25 sextant and artificial horizon in the backyard. I'll probably go the Astra IIB route before we shove off from shore along with paper charts and other non-high tech items for when Murphy's law kicks in and I need to find out where I'm not.

Ray

sailaway21 10-01-2006 10:47 PM

Celestial Navigation
 
Methinks I've pricked a boil here somehow. There are certainly differences in philosophy of what constitutes responsible navigation procedures. The US Navy is entitled to theirs. They've made mistakes before and will again. The landing ay Inchon was delayed three months because somebody decided they didn't need all those wooden hulled mine sweepers from WW II. That's the navy. You say government, I think post office. Because I hand my shipmate a GPS doesn't make him a navigator. And, every ocean going vessel out there now has a GPS. It's too fast, accurate, reliable, cost effective, and relatively trouble free to otherwise. Radar was the same. The average non naval vessel does not have the government behind it to fly out spare parts. When a generator spike frys all your electronic gear the mate on watch has his chart with his fixes plotted. He doesn't lose his set/drift data, it's right there on the chart table. If computers, of all ilks, are so wonderful (and they are) why does everyone request a hard copy of any important information that they do not wish to lose? Sure, we use GPS but we've got a sextant and a chronometer standing by. Coast Guard board of inquiries take a dim view of groundings based on a lack of navigational ability. Every ship still slides down the ways with a sextant and two chronometers on it. Lloyd's and any other marine insurance firm won't have it any other way. Back in the seventies, it was accepted naval warfare planning that, in the event of war with the USSR, the first thing that would be done is the shut down of the Transit system(NNSS-navy navigational sat. system) and that ships would run with no electronic emissions as well. No radar, radio, etc... Now if that wack job in N. Korea decides to launch a better missile, and we figure he's using GPS to guide it, how long do you think befere the plug gets pulled? Now, getting back to Argos original question I think that, contemplating an ocean crossing he has an entirely reasonable approach. It's simple, reliable, and doesn"t cost that much when you consider the components are good for more than a lifetime of use. If you would rather use redundancy of GPS receivers (and a good lead line) that's fine. Me, I can't keep a cellphone for more than two years without it getting wet or damaged somehow. I've crossed alot of oceans, and in my opinion, the test of any piece of equipment is it's reliability and what are we going to do if it fails. And to be honest, in a forum such as this, I suspect there are alot more people relying on a $100 widget to get them back home than what I'd wish. And real ocean navigators do pull the old hambone out from time to time just to keep from getting rusty, if not for the joy they get out of seeing that beautiful pinwheel on their chart. And why would anyone cross an ocean in a sailboat anyway, when there are alot more reliable, modern, mechanical, and electronicly equipped ways of doing so? But, fair winds and following seas to sir. "Curmudgeon"


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