Celestial Navigation Help Needed

[timgoz]

Dutton's has a companion workbook available to go with their classic work.

Also, the Florida Maritime Institute (Chapman's School of Seamanship uses their material) has a puplication that teaches basic Cel Nav with problems included. They include good worksheets for Sun, Lunar, & planet sights.

TGoz

[blahman]

Bill,

Something I've found while teaching new students aboard tallships how to get through nav problems, is that few people are really organized in how they write things out. I find it incredibly helpful to make each step very clear and to have things labeled. I'm /not/ a fan of some of the sheets available for helping one work problems out as you know far better than some standardized form how your brain works.

I know I'm not being too clear here, but my suggestion is to, if you're using a form for organizing info, to scrap it and work with a blank sheet of paper. Try finding some scheme that makes sense. If you write it, you know it. If you're just filling it in - ehh, not really. It really helped me to understand the whole picture, too.

Good luck!
Aaron N.

[Vasco]

Aaron,

Don't know if they still do this now, what with gps and everything but we always had a sight book when we were at sea. All sights were entered in this book and of course each individual had a slightly different format but all sights were in this workbook. The book went with you, along with your sextant when you went to another vessel. I still have my last one in the basement. The sextant I sold a long time ago.

[blahman]

Rick,

I've spent a great deal of time aboard SSV tallships, none of which used GPS for anything more than entertainment. While most students do work on blank sheets of paper, I keep a small blank-page artist notebook in which I've done all of my last sixty or shots. It's a great idea, not only for keeping track of what you've done, but for catching up after one has been out of it for a bit.

Cheers!
Aaron

[btrayfors]

Aaron, Rick, Bill, et. al

I take a slightly different view re: the use of forms. I think the problem with most forms is that they're cryptic and not well organized, not that they're a bad thing in and of themselves.

I used to teach celestial navigation, and found that an approach which often gets students "hooked" early on, and builds their confidence, is to teach the SIMPLE stuff first. Like the noon sight for latitude and the meridian transit sight for longitude. Toward this end, I developed several very simple forms to help both the novice navigator and the "backslider", like me, who haven't worked celestial problems in awhile.

I'd be happy to share these two forms with anyone, if they'll shoot me an email: bill at wdsg dot com

They're in pdf format and are very small files.

BTW, I really like the meridian transit sight for longitude. It's not used all that much, but I've found it really works, is reasonably accurate, and together with the noon sight for latitude helps to fix your position more precisely than, e.g., dropping a perpendicular from the DR position to the sunline.

Cheers,

Bill
S/V Born Free

[timgoz]

Loosends,

Out of curiosity, what is your watch "rate of error"? What kind of time piece are you using.

I have a Swiss Army pocket watch that has a rate of error of only (-) 1/15 sec. per day verified by SW radio time signal.

Take care.

Tgoz

[SkiprJohn]

Aloha Loose,
If you are doing noon sights or meridian passage sights all you need is the current year nautical almanac. My personal rule is that I buy a nautical almanac for each year to eliminate additional comupatations. I truly believe simpler is better. My meridian passage (noon sights) for longitude are not extremely accurate for longitude, i.e. within 5-7 miles but for lattitude are spot on. H.O. 249 I II and III are used for other types of sights.
I follow a form each time so that I don't forget a step. At sea on watch I get tired sometimes and with weariness can forget a calculation or do what you did, figure degrees instead of minutes, etc.. It helps me to have a form with explanations for each step.
I have an Astra IIIb which I can zero out on index error too and adjust it each time I take a sight. You are right about bumps and wiggles getting out of the box and temparature does sometimes make a bit of an error.
JohnL

[Loose Ends]

Using a timex, about 4 seconds fast/month compared to WWV

[daven]

Does anyone know if there is an online scource for a time signal check.
Thanks Dave

[btrayfors]

Dave,

time.nist.gov

Also, if you have a WindowsXP computer, it can be set to adjust computer time at the above location.

Bill

[millersail]

Originally Posted by daven

Does anyone know if there is an online scource for a time signal check.
Thanks Dave

Hey Dave,

Try these:

http://nist.time.gov/timezone.cgi?UTC/s/0/java (I use this one most commonly.)

http://tycho.usno.navy.mil/cgi-bin/anim

http://tycho.usno.navy.mil/what1.html?rwin=UTC

http://tycho.usno.navy.mil/utclock.html

All of these are subject to errors (usually pretty small) resulting from the speed of your provider's servers .. and anything else lying between your computer and the US Naval Observatory time clock.

There is also a telephone number which allows you to listen by phone to WWV: 303-499-7111

This too is subject to errors resulting from the speed of your telephone company's equipment/servers/repeaters/ etc.

Some additional links:
http://tf.nist.gov/general/broadcast.htm

The small errors that may exist between true UTC/GMT and what you read on the web page you choose, or hear on the telephone, can be easily checked against a wwv receiver, if you have one available. Remember though, that this error changes all the time with "traffic" on the servers and phone equipment/repeaters from minute to minute. (Wires, as well as space itself, allow the travel of these signals at the speed of light, for the most part. But the other stuff definitely can and does delay the signal.)

Having pointed out these variable errors, I must say that I have never taken a sight where the magnitude of such errors would matter very much to MY attainable accuracy with the sextant. But, at least you will be aware that these errors and potential sources of lag in time exist.

Hope this helps.
Robert

[btrayfors]

Bill,

Congratulations on your efforts to learn celestial navigation.

I used to teach it, some years ago, and have developed a few forms which make it VERY easy to do a noon sight for latitude and a meridian transit sight for longitude.

Would be happy to email you the forms if you think they could be of use. Just shoot me an email to bill at wdsg dot com

Bill T.
S/V Born Free

[NavPak ECS]

Someone asked if HO 249 needs to be replaced anually. This and other sight reduction tables are just tables to solve spherical triangles so they should last forever. HO 249 is popular, but it is limited to bodies with a declination of 22 1/2 degrees (N or S) or less. Some other sight reduction tables do not have this limitation, but are either more bulky or require more table entries to get a solution. My favorite method is to use a calculator to do the reduction. If you memorize the key steps for the astronomical and terrestrial triangle formulas, then you can solve it faster and more accurately with a calculator, even non-programmable, than you can by looking it up in the tables. I carry HO 211 as a backup to the calculator and computer.
Pelican Pete.

[DragonFlyer]

Bill, hi
This reply comes 2 years late, but what the heck. I believe your problem comes from your altitude correction. The proper correction is 14.5 arc minutes, whereas you turned it into 14.66 degrees (a 60x error!).

I have written a celestial navigation book which is free to download. You can get "The Armchair Celestial Navigator" at my web site: Celestial Navigation

Rodger

Originally Posted by Loose Ends

Hello all, I am new to the Cruisers Forum.

I am trying to teach myself Celestial Navigation for that SOMEDAY cruise.

I have read several books, Celestial Navigation for Yachtsman, and the Complete Onboard Celestial Navigator. BUT, obviously my thick skull will not let the information into the brain matter department.

Yesterday I took a sun sight using a ARTIFICAL HORIZON and got the following readings:

Sun Fix LL
lat 39.52N lon 75.08W (using my GPS)
7 sept 2006
Time 13 22 29 UTC
Local 09 22 29
Sextant Reading 61 deg 28'
Observed reading 30 deg 44' (above halved)
No Index error
No dip
Altitude correction +14 deg 40'

For a corrected sight of 44 deg 48'

My sight reduction tells me I am about 800 miles from where I am

What the heck am I doing wrong?????????????????

Thanks in advance and Smooth Sailing

Bill

[Talbot]

It is all very well for people who are taking sextant sites every night to be able to denigrate the use of forms. However, for most of us (me especially) I am very gratefull to GPS for making my life easier. My use of the extant is very infrequent, and thus for me it is essential that I have a good form with an idiots guide to where the data comes from and what I do with it. That way I reduce the possibility of error.

I have used a sextant for a long trip (Rio to Madeira) without any difficulty, so it does not hold any terrors for me, but I prefer to use the most accurate method of navigation available to me confirmed by as many other methods as possible. Thus sextant use is a nice link to the past, and a usefull fall back if all power goes.