learning celestial navigation

[jbarros]

ok, I''m not claiming I NEED to know this, and I''m not looking to start a flame war, I''m just saying I WANT to learn it, and was wondering if I could get some feedback from people who do, as to what a decent, inexpensive sextant is, and where I can find a decent book on the subject. How do I learn to do this, and once I can, how acurate can I realisticly expect to be?

Thanks

-- James

[fer@fer]

You better find a good book, and of possible a teacher too.

A simple approach is in Celestial Navigation for Yachtsmen by Mary Blewitt, Thomas Bergel

http://www.amazon.com/exec/obidos/tg/detail/-/0070059284/102-8364544-5309709?v=glance

You might also be willing to reach one of the best pages on this subject

http://home.t-online.de/home/h.umland/index.htm

And also purchase or download bowditch''s practical navigator http://pollux.nss.nima.mil/pubs/pubs_j_apn_sections.html?rid=187

As to accuracy, a 4 second error in your watch, represents 1 n mile.

Depending on the approch, 2/5 mile error is plausible. In my case is standard.

[928frenzy]

I learned it from library books. There are over half a dozen books on the subject just in my local branch.

I bought a used metal (aloy) sextant which tend to be more accurate and hold their settings better than plastic ones. I found it on ebay which turned out to be about the same price as a new plastic one.

Since purchasing it, I practice about once a month just to keep from getting rusty.

~ Happy sails to you ~ _/) ~

[BigRed56]

Ahoy, I gots me a real nice sextant at me church he ain''t a whole lot of good at navigation but wot the heck he''s about a usefull as CN ,and on a long voyage his predilection for young men comes in right handy. Lets see your sextant do that!! Pirate of Pine Island

[Priceless]

You can sail with your predeliction for young men, Pirate (of Pine Island). I''d rather sail with a sextant and a young lady.

Cheers you duffer, Frank

[jklewissf]

The precision of the measurement you make with a sextant on a small sailboat is limited by the motion of the boat. I have found that, regardless of the sextant I use I can routinly get fixes within 2 miles (at sea)...

I have a C plath sextant that was a gift. They are very expensive to buy and I think its an inappropriate model for a small boat because it is so heavy. It might have been a fine choice for a freighter where the office could stand on a rock stable bridge and shoot the sun once and rely on the sight. I have found that, on a small boat, I need to repeat the sight several times to satisf myself that Im getting reasonable answers. You can either accept one of the sights of the set or plot them and pull an angle and time off the plot.

Because taking a few sights is a good idea I think the most appropriate of the metal sextants are the ones made by Frieberger (sp?) in Germany. They are slightly smaller that the C Plath and are aluminum so they are very light. They dont take up quite so much space either.

Plastic sextants work fine too. As with the metal ones always check the index error every time you use it.

I learned with the tables for air navigation but have switched to the tables that are built into the nautical almanac these days. I figure I would only use celestial as a fall back and dont want to carry extra books when the tables in the almanac will do the job (slightly more tedious).

Celestial is shrouded in mystery but it is really pretty simple. Once Nathanial Bowditch figured out a way to do the spherical trigonometry solutions using precomputed tables the sailor''s math skills only needed to be good enough to do addition and subtraction in degrees, minutes and decimal minutes. nowdays many calculators can do these calculations in decimal degrees and switch the values back to deg, and minutes for use with the tables.

This is a good skill to have. Its easy to learn. But dont spend so much on the sextant that you cant afford a spare GPS or two. When I sailed my boat from San Francisco to Hawaii a few years ago I did not see the sun until I was halfway to hawaii...But I always knew where I was within 86 feet, thanks to GPS.

John

[rodupes]

You can get some very good c.n. literature at the naval academy in annapolis md. might even have some used for sale i'm not sure but it's worth a try. i'll check to see if still have anything from when my son was at the academy . maybe he doesn't want it any more.

[sailingdog]

One problem with the plastic sextants is that they tend to warp, and the warping makes them useless.

I'd second the recommendation for Mary Hewitt's book, and add

The Complete On-Board Celestial Navigator, which is a pretty good book and has the tables for up to the end of 2007 in it as well.

I'd only recommend buying a used sextant from a reputable seller... as they can have serious problems if they've been dropped or abused. A reasonably priced metal sextant is the Celestaire Astra 300B, which is about $500 new.

[TXS-ALAMO]

Rodupes, do they still teach celestial at the Naval Academy? I thought it went the way of morris code down to Davy Jones's locker.

[sailingdog]

AFAIK, they do teach use of a sextant, but all the computation is done by navigation computers instead of doing the math out by hand.