Want to Learn Celestial Navigation

[Bruce Cumming]

Sorry. Should have said CG Auxiliary. Bruce

[Joe CD MS 300]

CN is a skill that unless you are going offshore and making landfalls is akin to being able to start a fire without matches. There are a lot of nautical skills that fall into that category for the average harbor hopper. It's different for a long distance cruiser where you never know what skill you might need in a random circumstance. Given the cost of a decent GPS its is almost unseaman like not to have a GPS and know how to use it.

Just pilled this off the internet quick. My guess for the average (not expert) casual CN / sextant user a 5 mi error might be typical.

Accuracy
Sextants measure the angle between the sea horizon and a celestial body. These angles are measured in degrees and minutes of arc (1/60th of a degee). Measuring this angle to an accuracy of 1 minute of arc (1') will result in a positional accuracy of 1 nautical mile. Accurate sextants can measure this angle to an accuracy of 0.2'. This means that theoretically one can determine their position to 1/5 of a mile. Additionally, a good clock is required to accurately compute the GP of the celestial body. An error of 1 second in the clock will create a positional error of up to 1/4 of a mile.

A good navigator with an accurate sextant and clock can determine their position to within half a mile. Of course, if you're on a small boat that's bobbing around, you'd be happy to get to within a mile or two of the correct position.

[tartansailor]

Please feel free to bmail me for answers after you make a good and faithful effort. Sincerely, Dick

[Jim Davis]

CN is a skill that unless you are going offshore and making landfalls is akin to being able to start a fire without matches. There are a lot of nautical skills that fall into that category for the average harbor hopper. It's different for a long distance cruiser where you never know what skill you might need in a random circumstance. Given the cost of a decent GPS its is almost unseaman like not to have a GPS and know how to use it.

I don't think anyone is disputing you. On Isa Lei I have three GPSs, two fixed and a handheld. When underway the two fixed sets are on and in constant use. The handheld is normally only used to take the dog ashore when the fog is so heavy I can't see the beach.

I also have paper charts, tide and current tables which are regularly used. The paper and tables are always on board even when "harbor hopping". The ability to navigate without electronics provides a good back up and helps me stay aware of the entire situation. I do not consider it prudent to operate solely on electronics. The charting data in even the most expensive chart plotter is no more accurate than a current chart and the dependence on electronics leads too many into a false feeling of security.

As to celestial accuracy, a five mile fix is about right from a small boat, perhaps a mile if on a ship. There are also limitations caused by weather and fog. I would not consider running onto a dark coast line with out having a recent fix. I have laid to over night so I could run in during daylight. Also when relying on celestial I have intentionally made my landfall offset so I knew which way to turn and run along the coast until I reached the inlet I wanted.

Is celestial necessary, clearly no, but on the other hand it does make for an interesting hobby, with practical applications.

[Joe CD MS 300]

I also have paper charts, tide and current tables which are regularly used. The paper and tables are always on board even when "harbor hopping". The ability to navigate without electronics provides a good back up and helps me stay aware of the entire situation. I do not consider it prudent to operate solely on electronics. The charting data in even the most expensive chart plotter is no more accurate than a current chart and the dependence on electronics leads too many into a false feeling of security.

As to celestial accuracy, a five mile fix is about right from a small boat, perhaps a mile if on a ship. There are also limitations caused by weather and fog. I would not consider running onto a dark coast line with out having a recent fix. I have laid to over night so I could run in during daylight. Also when relying on celestial I have intentionally made my landfall offset so I knew which way to turn and run along the coast until I reached the inlet I wanted.

Is celestial necessary, clearly no, but on the other hand it does make for an interesting hobby, with practical applications.

I agree with everything you said. Its just that sometimes there seems to be a reluctance to acknowledge how incredibly accurate and reliable the GPS system is as if it would offend the ghosts of sailors past. Yes, you need to be prepared for some type of failure. Most likely it will be with your GPS hardware not the GPS system its self. I have had batteries go dead, a screen go bad but I have never experienced a GPS system failure or not been able to get a fix with any GPS I have owned. Given the number of redundant satellites and the reliance on the on the system by the military and the airlines I think he possibility of some kind of major system failure very remote. Not to say you should not be prepared for it.

Although I have not come across any charting errors or position errors with GPS I know that "stuff" happens and try to confirm with other means the info I'm getting from the GPS. One of the best tools is the ability to overlay radar on the chart. It confirms both your position and the chart info on the chartplotter.

[WaywardWind]

"

Slide rules have gone the way of the dodo bird

Really?
Have you ever tried?
Did you ever loose a HP 48SX to salt spray?
May I respectfully suggest that you have your eyes examined.

Dick

If you will PM me, I can explain how a slide rule works. I've been handy with a slip stick since I bought one in 7th grade and taught myself how to use it. It's simple, really, once one has a slight acquaintance with the concept of logrhythms, but one must differentiate between precision and accuracy.

Basically, a slide rule makes multiplying and dividing 2 and 3 digit numbers to give an answer accurate to 3 digits (for mulitpliers/dividers/answers between 1xxxx and roughly 2.5xxxx) with an estimated 4th digit, all other answers accurate to 2 digits, estimated a 3rd digit.

A slide rule is a guestimating tool when one doesn't want to use pencil and paper to calculate products and divisions. Candidly, guestimating 2 digit multiplications in the head is easier and quicker and just as accurate even if less precise. Besides, bamboo slide rules don't like the humidity on a boat, while metal and plastic rules don't like the temperature changes.

In lieu of a slide rule, a printed table of 3- and 4- and 5-digit multiplications can be printed off the Internet (they are no longer available in office supply stores), sprayed with waterproofing, then stored in some safe place for use as might be needed. Divisions can be done from the same table.

BTW, if lightening takes out all the gps's on a boat (including the one in the Faraday Gage oven), it usually also takes out all the electronic watches onboard and likely the SW radio with its time checks. Then you gotta sail east or west until you see land and stop at a gas station to ask directions.

BTW, some time ago, a college professor from New Jersey circumnavigated without ANY nav instruments of ANY kind, including no lead line. No watch, no sextant, no strings on any measured piece of wood, no shadows from measured pieces of wood, no radio, no pieces of glass glued together, no nothing.

There used to be a printed card (available from Davis?) about the size of a sheet of typing paper and printed on hard plastic which could be used, as is, for emergency navigation. If you want, you can use the width of the your extended fist (about ten degrees) to do a good job of figuring latitude, and if you know what day of the year it is and are in the Northern Hemisphere, you can tell time reasonalby accurately by the position of the Big Dipper.

Edit: That card is available from Amazon for a bit over ten bucks, plus others.

That college professor is Marvin Creamer, and he was 68 years old when he completed his circumnavigation. It seems he is still alive and age 93.

[Carl Thunberg]

The booklet that comes with the Davis Mark 25 sextant is pretty good for sun-sights. Sun-sights don't require a nautical almanac because the sun is in the same position at the same date and time every year. For practical purposes, you can ignore the effect of leap-year. Planets move around relative to the stars and to each other, so you'll need a nautical almanac for celestial bodies.

If you want to just get your feet wet with sun-sights for a while, you can get to that point pretty quickly. That's the way a lot of people start. It gets you used to the mechanics of taking sights while keeping the geometry pretty simple. After that, if you want to advance to celestial bodies, that'll take some study.

Remember, the sun doesn't care about daylight savings time. You could find yourself taking timed sun-sights for two hours waiting for the sun to reach its zenith. I learned that the hard way.

[ckreitlein]

Try the next one....

[ckreitlein]

[Forrest]

For anyone who wants to learn a little bit about celestial navigation, here is a link to a 4 video series (about 27 minutes in total).

http://www.youtube.com/watch?v=BMoWQoKm ... XE4XaQU64E

Cheers,

Forrest

[Bill Goldsmith]

I think it depends on your preferred learning style. I have always wanted to make the time to take the courses offered at Mystic Seaport which are not terribly expensive: See e.g.: http://reednavigation.com/intro-class/

But that's just me--I like the class environment and the ability to ask questions immediately as they come to mind.