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post #3 of Old 10-01-2006
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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!
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