ITS TOO EASY THESE DAYS TO GO TO A LOCAL SHOPPING MALL TO BUY A GPS.IF THOSE WERE AVAILABLE 20 YEARS AGO THE WAY THEY ARE TODAY IT WOULDNT BE THE SAME.SEXTANTS, NAUTICAL ALMANACS,PLOTTING SHEETS,SIGHT REDUCTION TABLES ARE PROBABLY UNHEARD OF BY MANY BOATERS TODAY.BASICALLY CELESTIAL NAV PRACTICES,ONCE ACHIEVED ALLOWS THE NAVIGATOR TO TAKE A PLAIN BLANK PIECE OF PAPER,AND WITH JUST A FEW SIMPLE TOOLS A LATTITUDE AND LONGITUDE GRID CAN BE DRAWN UP FOR ANY LOCATION.(THAT IS TO SAY THE LONGITUDE LINES WILL BE PROPERLY SPACED FOR ANY GIVEN LATTITUDE)TOO MANY PEOPLE ARE OUT ON THE WATER IN MULTI-MEGABUCKS BOATS AND EVEN WITH ALL THE ELECTRONC GADGETRY STILL CANT DECIPHER A NAUTICAL CHART.I WILL AGREE THAT LEARNING CELESTIAL NAV IS LIKE LEARNING LATIN....IT IS A LOST OR DYING ART.BUT BEFORE I GO ACROSS THE OCEAN I WILLGET A GOOD METAL BODY SEXTENT AND ALL THE ASSOCIATED TOOLS AND PUBLICATIONS NEEDED TO USE IT.ON MY SECOND RETURN TRIP FROM HAWAII TO CALIFORNIA I WAS GETTING ERRONOIUS READOUTS FROM A VECTOR TWO LORAN RECEIVER.IT TOLD ME THAT I WAS TRAVELLING IN A ZIG ZAG PATTERN FROM DAY TO NITE.I ACTUALLY HAD TO REVERT TO USING A WW2 ERA SEXTANT TO GET A PROPOER POSITION AND I KNOW FROM EXPERIENCE YOU CAN NEVER DOUBT THE POLARIS SIGHT.THAT ZIG ZIG READOUT THAT I GOT FROM DAY TO NITE PROBABLY WAS CAUSED BY RADIO WAVES TRAVELLING DIFFERENTLY FROM DAY TO NITE.ANYWAY MY SUGGESTION TO ANYONE VENTURING BEYOND THE HORIZON IS JUST BE SURE YOU ARE READY FOR ANYTHING.BECAUSE NO NATER HOW MANY THOUSANDS OF MILES OFFSHORE YOU ARE,YOU ARE NEVER MORE THAN ONLY FIVE MILES FROM........DAVY JONES LOCKER.AND THOSE THINGS DONT JUST HAPPEN IN THE MOVIES OR ON TV...THERE ARE MANY WELL FOUND STRONGLY BUILT SEAWORTHY BOATS ON THE BOTTOM.
Good point Eric,
In the area where I sail, we experience something called a 'SRA' from time to time. They are usually announced in the paper and local radio stations. The military can induce an error, a liner offset (I was moving 9 knots, at the dock) or just eliminate the signals from the GPS all together.
Imagine you are 75 miles from Bermuda, and something bad happens ('bad' in a homeland security sense of the word).
Hum.... How much food and water DO you have onboard?....
BEFORE I VENTURE BEYOND I WILL HAVE ENOUGH TO LAST NO LESS THAN NINE MONTHS HOWEVER THE VOYAGE I WANT TO DO WILL ONLY BE 5 OR 6 MONTHS.AND THAT IS TAKING MY TIME.IF I GO INTO A HURRY UP MODE I CAN ACCOMPLISH THIS NEXT TRIP IN LESS THAN 5.THERE IS STILL MUCH STUDYING TO DO AND PREPARATION.HOWEVER I WILL IN FACT "KEEP IT SIMPLE......."
I will go so far as to carry a slide rule for doing site reductions without site reduction tables. If I lose my slide rule, I can compute my table of sines, if need be.
Math is fun, and Celestial is very, very cool. :D
(my personal best fix, though from a beach rather than a pitching boat, is 2 nm from actual position. That was with a Davis Mark 15).
well I used one of those tamaya 3/8 size mini sextants,and came up with 3 lines that cross in an area the size of a match head.that was on a replica of an 1800's era clippership half way to nowhere.
KISS,
I have been know to navigate in pea soup with a compass, leadline, chart and watch in Casco Bay, Maine. Does it get simpler than that :o?
I thinking about getting one...a cheap one for training and learning on...and was wondering if anyone in N.C. I might could get up with and learn.
I figure I could use the training and I can atleast start useing it before I go out to sea.
Bill
my advice to you is to get a good metal one.the index error (or to say by how much it is innacurate) varies greately with any plastic bodied sextant.you can be this accurate tho...place a half dollar coin on a plotting sheet...you will be anywhere with in the diameter of a half dollar coin at best. its because plastic compared to metal is very unstable... in the sun its micro dimensions can change minute to minute and this becomes very apparent when you read the arc. even with a metal body one....when you take it out of the box and place it in the sun....you must let it set for a few minutes to let the index error stabilize.with any metal bodied one you....well atleast I....have come up with 3 lines that cross ....on a plotting sheet....in the area the size of a match head....just a few square miles.depending upon your lattitude a standard vp-os plotting sheet(if you are unfamiliar witht that term look it up on any search engine) covers about 250,000 square miles.as far as learning celestial there are various aspects of it.... but simple sun lines can be accuratly and intensively learned in one day.....but you have to do nothing but sun lines all day.if you do get into doing this dont let the mathematics scare you.its nothin more than simple addition and subtraction in groups of 60...that is to say 35 minutes + 35 minutes does not= 70 minutes.its" 1hr 10 min." its also as easy as figuring your taxes but theres no cheating.very simply put ,numbers are retrieved from various publications and applied to a formula.even so before you can take algeobre 2 you must take algeobra 1.before you do celestial it is a must that you can proficiently do basic navigation.....you shoud be able to plot courses,figure speed time distance, (you know that 60d=st thing)you should be able to proficiently read a nautical chart
A fellow in New Bern named Tad Michel tought us celestial nav
We also bought an Astra 3 from him them as well
He had great lessons
Not sure if hes still teaching it but tell him I sent you
Send me a personal message and Ill give yoy my email and phone number
Iceman
I would be happy to learn sun lines now and once
I have figured out how to do that, maybe try to learn the rest of it. I want to beable to have a back up for a G.P.S., so as not to end up in Detroit while looking for Bahama.
thanks.
Bill
There are a couple of web sites that provide various calculators useful for practice. I do my site reductions "by hand' with a calculator or slide rule. This eliminates needing the site reduction tables and errors introduced in interpolating the table data. Most folks will want to use the site reduction tables, so it's a matter of choice.
Also, I don't like buying an almanac each year. When I do buy one, I buy Reeds; it contains a LOT more than just the ephermerides of the celestial bodies, such as ABC tables (an alternative to using the standard site reduction tables) tide charts and chartlets for major ports. In addition, Reeds has good info on how to do CN that is easy to follow, no matter what method you use to reduce sites. In other words, Reeds is a good stand-alone book - you don't NEED any other books or tables to do CN, and it CAN be used for TWO years if you want to do some extra calculations.
When land bound and practicing, I use online resources, such as:
1. Cel Nav Data (http://aa.usno.navy.mil/data/docs/celnavtable.html)
On this one, you input your assumed position, date and time and get essentially an almanac page. Includes stars, planets and moon. This is essentially an online epheremerides, or your online almanac.
2. Transit Times (http://www2.arnes.si/~gljsentvid10/trantable.html)
Tables of transit time and declinations of five major planets. Also includes equations and links to download the entire tables.
3. USNO List of Data Services (http://aa.usno.navy.mil/data/)
Links to many helpful and informative pages from the US Naval Observatory (including the two linked above).
4. Cel Nav Resources (http://aa.usno.navy.mil/faq/docs/celnav.html)
Also from the USNO, links, addresses, etc useful for Celestial Navigation.
(These USNO links in turn contain links to where you can download site reduction tables if you don't use an online or calculator based method).
Also, Henning Umland provides some free javascript based site reduction calculators (a really good way to check your site reductions as you learn) and almanacs..visit these web sites and save the pages (you don't have to be ONLINE to use them, the calculator is actually stored on your computer, so you can put them on your shipboard laptop and not even fool with manual site reductions:
Site Reduction Calculators and Almanacs (http://www.celnav.de/page3.htm)
And finally, FYI, Bowditch, a must read for those serious about navigation and pilotage, is available online for either full or chapter by chapter download:
Nathaniel Bowditch, the American Practical Navigator (http://pollux.nss.nima.mil/pubs/pubs_j_apn_sections.html?rid=187) This is the 2002 edition.
kewl thanks for the links. I'm going to stick to the sun readings first. I have a very limited understanding of how to do that. maybe in 5-6 years I'll understand this stuff. lol
thanks,
Bill
I like Reeds also, and have the companion, the 2006 almanac.
Sadly they elected to remove the sight reduction tables from the almanac (last year? Two years ago?)
http://www.reedsalmanac.com/
You can purchase a separate book 'Reeds 2006 Astro Navigation Tables'
I have all three right here next to me at the moment. ;D
Quote from: hearsejr on January 09, 2006, 07:41:09 PM
kewl thanks for the links. I'm going to stick to the sun readings first.
Bill,
Those links and calculators, etc, are useful for doing sun sites. I use them for that as well.
Quote
Sadly they elected to remove the sight reduction tables from the almanac (last year? Two years ago?)
I did not know that! :(
I do not use reduction tables anyway. I can crunch the numbers with a regular calculator (the equations are simple) just as fast, and do the same with a slide rule almost so. It elminates the need for the extra books (SRTs), but is not approach for everybody.
thanks, I got a couple of good higher quality calculators, both with solar cells and they work great. ofcourse I've never even seen a slide rule :o LOL
if you really want to get a good idea of the celestial nav process,once you learn basic sun lines then get all your toys together and go for a long ride up and down the coast in your car.take sunlines along the way at various stops.for wwv time I brought the short wave receiver with me.take as many lines as possible and record the info on paper(tme and arc reading)then go home and worke out all the sights and see how well you tracked the motion of your car.moving at that speed the lines will show drastic changes.
Quote from: starcrest on January 10, 2006, 12:01:42 PM
if you really want to get a good idea of the celestial nav process... go for a long ride up and down the coast in your car.
That's a really good idea. You don't HAVE to be on the coast, if you use an artificial horizon (essentially a pan of water on the ground). This adds one extra conversion (since Hs will be off by a factor of two), but is excellent for sextant practice away from big water.
kkkkkkkkeeeeewwwwllll!!!!!!! I gotta try that! maybe I can start early in the morning, and shoot down the outer banks and try it. it'll give me a reason...eeerrr excuse to run down the beach. lol.
thanks for the idea.
Bill
I like ghosting along close in to shore just as the sun is coming up and the water is like a mirror. But this leads to some tricky navigational problems. I am always amazed at just how many things can be used to navigate a boat. Dogs barking, the sound of doors slamming as someone lets their dog out for it's morning romp, cars starting or driving down the road, the morning train, fishing boats or simply the sound of fishing boats returning to port after a night of working the coast. When all these things are recognized as tools you are able to constantly refine and reduce your position to a point that you are no longer making an educated guess as to where you are on that chart, you KNOW.
staying to close to a shore line can lead to trouble.next thing ya know yore walkin home
the artificial horison is something I never tried .it is not as easy as you think.the suns image needs to be brought down to the reflected image in the water...I just dont think that method is very accurate compared to bringing the image down to the actual horison.plus the azimuth....that is to say the true direction to the sun ...thats the direction that you look...I dont think its a very accurate method.the shadow given off by the pintle of a sundial....delineates passage of time....that shadow when followed to its source.....thats azimuth.some how I think the shadow given off by a bucket of water is too ambiguous to be relied upon.any way I am not in N.C but I can and have taught the stuff
I use an artificial horizon for sextant practice. It is very tricky, and takes a lot of patience. I was once trying to teach a lady to use the sextant with it, and she just could not fix the sun's image in the water. I think it's a useful technique to know about, and good for practice, but it does add some difficulties that a newbie might well find overwhelming.
I once used an aviation sextant that was modified for marine use.the bubble had to be removed,and it was only good for the sun and moon but it worked.I understand the actual use in an aircraft was quite a stunt.that height of eye correction would have been phenomenal
bet it was feat back in the 30's to learn that stuff from an airplane then getting sent off the South Africa in ww2. I would hate to have to do it. look up the story of the B24 called "Lady Be Good" . they got lost after a bomb mission and over flew their base by 400 miles and bailed out thinking they were over the med, but they were realy over the dessert. I think they walked like 350 miles trying to get back to the base, and 1 by 1 they all died. the plane was in such good shape when they found it that some of the radio equiment was used to reapair a busted unit on a hellicoptor they using during the search for the remains of the crew. they found it in like the late 50's. very inteeresting reading for anyone.
I was looking at the set from Ebay, the guy said he was willing to take like $150 for the sextent with case and manuels. I backed out after he said he did not know if it had everything or not and he would not refund the $$ and would not check to see if anythingwas missing or broke..he claims to already boxed it up for shipping.
I still thinking Ebay is where I'll get the first one from then I'll thinnk about getting a nice one from the Latt's and Att's ad I saw.....somethinng $500 though, and it may take a while to save it up. lol.
Bill
This is a good thread - thx guys. :)
Re: the Lady Be Good story - I've read about that. Amazing that they found the plane, out in that desert. And even later, the remains. Interesting story.
I wonder if there are still a lot of miltary surplus sextants around? Based on the eBay price, doesn't look like many...
I wish
I had snatched the old navy one up back when I had a chance. the guy had the whole nine yards, the compass in a wooden box, the sextant, the pertractors, the ruler, and survival book from a life boat. all for $50. oh well should've ..could've..would've's are the stuff dreams are made of right? lol.
bill
NOAA has a free online chart service offered. It has posted all 1000 and some charts on line. These are all up to date with most recent Notice to Mariners. Recommended use is for a planning tool or quick access.
Site is below
http://www.nauticalcharts.gov/viewer/
Click on your water area and then needed chart numbers.
Zen, I did not see anything listed as "ducking coast" ;D
Connie- if you are taking about the ENC charts, they are pretty much worthless for navigation purposes. Laura and I had some aboard last year, loaded on our laptop. They don't give you the info you need.
Looks like the new release of charts may be much better but we haven't had time to check 'em out yet.
Charlie, These are supposed to be the actual Govt. Charts, updated with the Notice to Mariners and to be used for planning purposes etc. It did recommend that you use your digital charts or purchased charts for actual cruising.
These may be good to use when doing global pre-planning or using them to update your hard copy charts.
Problem I had, looking at it on small computer screen, you zoom in and you only see a small area, when backed out, I could not read the depths etc. May be my 40 something eyes too. :)
Check it out when you get time Charlie and give us some feedback on your thoughts.
lol- "when we get some time" ;D
SOON I hope.
Back in November I began a new building here at the house to move my business into (woodshop/boat building). We have moved but are now neck deep in clearing the old building and trying to set up a "garage sale" to rid ourself of as much "JUNK" as we possibly can. HOPEFULLY by next month we'll be clear of that city, we won't have to drive there any more and we WILL have some time to look over the new charts and MAYBE even sneak in a sail.
Gee I hope so ;D
one more thing I jus' remembered.this celestial stuff is all predicated on a falacy.it really should not werk at all.it is based on the geo-centric universe theory.in other werdz,the oith iz da centuh uvduh yooneevois,an' evry tink revovles around it.iz dat tru? iz da oit da centuh of da yooneevois?theres that nooyawka in me comminz out.sorta like the hulk when he gets mad
Utterly newbie question here . . . in scanning eBay, I see really, really expensive sextants, and then---I see ones like this:
http://cgi.ebay.com/HENRY-BARROW-Working-6in-Sextant-w-Box-Excellent-Gift_W0QQitemZ7384912685QQcategoryZ37971QQrdZ1QQcmdZViewItem
So, the question is---do the "brass working reproductions" do the job, or are they just "for pretty?" ???
NANP
I have seen those the problem will be reading the arc...it may work fine...as long as you use the rite numbers...but the arc is the vernier type with that magnifying lens the read out may be difficult.I prefer the micrometer drum type by all means.and yes...sextants are great fun when you know how to use them.it aint hard at all...simple addition and subtraction in groups of 60.....35min+35min=1hr 10min.ya shood b'ableta getta good yoozd metalone fora boutz 200 bux at a marine consignment place ore jusgetta astra 3b ifya like chinese food...ifyaz wanna go allout get da won wally krankite has its silver an' costs 35 gozillion billion bux.but all kidding aside...definately learn what its about.its a real discipline.....it doesnt take long....just acoupla days of intensive practice an'yul havit memorized.if you are indeed really serious about the celestial stuff then start with the davis mk 2...dont worry about the fancy see thru horison mirror..it wont change the fact that it is plastic and vulnerable to serious index error they are good to learn on....then when you see the difference a metal bodied one makes you will take tha plastic one and seriously wrap it in its box and save it for emergency use only
Nanp.. Don't waste your money on those Ebay reproductions.They are stricktly display items with some moving parts. If you must have a metal sextant go with the AstraIII for the money.. you can catch them on ebay for around 500. Personally for use on a sailboat i recomend the davis 15 for the light weight. Plastic sextants have good accuracy if you adjust them after each use. I can get 6 mile intercepts with my 20 dollar davis mark 3 ..
Thanks, Lars, that's exactly what I wanted to know!
As a vintage-inclined gearhead in general, it's a bit hard to make myself consider anything with the word plastic in it . . . but the difference between $500 and $20 might just force the issue! ;)
I mean . . . that's like, a box of Cuban cigars and a case of Scotch, right there.
NANP
You might try these sites:
http://www.starpath.com/catalog/courses/1701c.htm
http://www.irbs.com/bowditch/
Wow . . . great links, Joe! Awesome! :o
I've already started transferring the Bowditch manual to my hard drive . . . and poking around the rest of that site.
Good karma to ya; this'll keep me busy awhile! ;D
NANP
actually the intercept is the distance that the resultant line of position is plotted perpandicular to the azimuth ....either to or from the assumed position and has no bearing on instrument accuracy at all.there is a "long intercept" method that can be used when the proper sight reduction tables arent available.'INDEX ERROR" is what the difference is between plastic and metal instruments.this needs to be corrected before the sight is taken and is one of the first corrections introduced when figuring the Ho,or height observed.even with the best plastic instrument this can be up to plus or minus 30 minutes.which basically means an error of 30 miles. Even so,the first sight,or the Hs,(sextant height) under the most optimum conditions can be perceived differently between 2 or more different people.even your own two eyes my get a different readout at the same time.this is a neurologic thing.with the ww2 david white I used it was never more than -.5,or less than 1/2 mile basically the width of a pencil line on a plotting sheet,so I just left it at zero.I used the davis ..the one with the traditional split horison mirror and have seen the index error change rite b4 my eyes.basically I set the micrometer to zero,sighted the horison,and b4 I knew it there were 2 horisons.these things are ok,but actually my garmin 12 channel gps is far more accurate and prefer to use it even more than walter cranshafts silver bullet
Quote from: starcrest on January 29, 2006, 06:01:40 PM
'INDEX ERROR" is what the difference is between plastic and metal instruments.
ALL sextants, plastic or metal or made of cheese will have a finite Index Error.
Quote
this needs to be corrected before the sight is taken and is one of the first corrections introduced when figuring the Ho,or height observed.even with the best plastic instrument this can be up to plus or minus 30 minutes.which basically means an error of 30 miles.
No it does not. Not if you know what the index error is, and you correct for it. If you subtract (or add, as appropriate) the IE from your Hs, the IE introduces NO ERROR to the calculation. Every CN book I've every read, and the CN exercises in Ocean Navigator (a PROFESSIONAL trade mag) have included correcting for the IE as part of the process. Therefore, the finite IE of the instrument itself is corrected out, so, a IE of 30 minutes (which would be very very large, by the way, my Davis Mark 15 typically has an IE of about 2-5 minutes, and again, I KNOW what it is before taking a measurement) absolutely does NOT introduce an error in the resulting fix of 30 miles.
With the Davis 15 plastic sextant, it is trivial to zero the mirror to 0 IE before you take a reading. Even if you don't want to do this, it is equally trivial to measure the IE by nulling the horizon itself.
You can get quite accurate readings with a Davis mark 15 plastic sextant. Period.
before or after makes no difference.how ever a difference between"minus point five" or two to five is a huge difference resulting in as much as 2-5 miles.still I will swear by my garmin 12,which yeilds an error of 6 feet,or about.001 nautical mile
Quote from: starcrest on January 31, 2006, 07:23:43 PM
before or after makes no difference.how ever a difference between"minus point five" or two to five is a huge difference resulting in as much as 2-5 miles.still I will swear by my garmin 12,which yeilds an error of 6 feet,or about.001 nautical mile
Look, Eric, I don't know what you are talking about. If you correct for the Index Error by subtracting it out, IT INTRODUCES NO ERROR IN YOUR FIX.
Prove to me otherwise, mathematically, that if you have a measured angle that you KNOW is too small by X and you add X to the measured value, how is that not the REAL VALUE?
The error in fix in CN comes mostly from two places: error in taking the measurement itself and in knowing the time that the site was taken. CN can reliably give a fix to wthin 4 nm (which historically was 'good enough' since that is less than the visible radius from the maintop of a square rigger, or even from the deck of an Ariel). While metal sextants do tend to be a little better, if you know the limitations of a plastic sextant (ie, determine the index error for each site), they are about as good.
That four mile precision using CN is true whether you have an Index Error of 0 minutes or 10 degrees - IF you KNOW what the IE is. It does not matter.
Many professional navigators, as evidenced by years worth of articles in Ocean Navigator, do not rely SOLELY on GPS; in fact, they recommend against relying on any one technique alone. Further, many of these same professional navigators keep plastic sextants as backups or even as the primary tool in the 'abandon ship' gear. CN is a great hobby, and a useful one. And there is no need to drop $500+ on a high grade metal sextant while learning the art when a $120 plastic model will serve just fine.
CN vs. GPS is another discussion completely. No one is claiming CN to be as precise as GPS, but please don't cloud the issue with nonsense that KNOWN Index Error cauaes an error in the computed fix. I don't think you really believe this to be true, since I gather from your discussion of CN that you really do understand it.
index correction is the amount of error in the arc itself.simple changes in air temp makes the actual material that the instrument is made of change ist shape --in heat it expands in cold it contracts,plastic is very unstable in this sense.when using my david white ww2 navy surplus,it would be in the box in the relative coolness of shade.once brought out into the hot sun the metal the it is made of would expand....not in the way you could see by eye.....but this is very definite when looking thru the horison mirror."if its on its off,,,,,if its off its on"in otherwords some times the error is negative (then its added)and vise-verse.I am basing my experience on 15000 mile of celestial nav use.
Quote
index correction is the amount of error in the arc itself
Not exactly.
It is a mirror alignment problem that is very easily measured, should always be measured, and once you know the IE, it's effect on the instrument introduces no error in the fix obtained from a given site.
Index error is the the reading on the instrument when the horizon is 'nulled.' That is, when you are looking through the sextant and you see one solid image, the sextant is 'nulled.' If you must adjust the sextant to a non-zero reading to get this single uniform image, that reading is the Index Error. It is trivial to measure, and if you determine the IE right before you take a site, the thermal properties of plastic have nothing to do with it. Any changes to the shape of the sextant in the few seconds from measuring the Index Error to taking your site will contribute less 'error' than a human's ability to precisely drop a celestial body to the horizon.
Good and Brief Description of Index Error (http://en.wikipedia.org/wiki/Sextant#4._Index_Error)
Or Here (http://www.tecepe.com.br/nav/inav_c12.htm) (scroll about 2/3 way down the page)
Or Here (http://www.clipperlight.com/howusesextant.html) Notice that it says to determine the IE before each use.
Or Here (http://www.seasources.net/Corrections_to_sextant_reading.htm) Again "you check for IE each time you use the sextant."
And Finally Here, Too (http://www.sailnet.com/sailing/97/tecjan97.htm)
This is my last post on the topic, since we are getting nowhere. You can think what you want about plastic sextants and index error, and I'll continue using my Mark 15 to get fixes acceptable to me.
getting nowhere ...sounds good ...remember even if you are nowhere you are never more than 5 miles from......
Hey guys -
Don't stop talking yet - the discussion, though frustrating it may be to be at loggerheads about part of it, is yielding some good info and links for those of us who are rank n00bies at CN. :)
$120 for a plastic sextant? Too expensive!!! My Davis 15 cheapo was only $35. ;D (Just kidding, I know what you are talking about...) Supposedly the 15 has been/gets used by people as their primary sextant, and as a liferaft tool as well. Personally, if it's accurate enough to get me close enough to somewhere that I could do coastal piloting, I think that that is pretty darned good. Better than what Magellan, Cook, Colon, Polynesians, and others had back then, and look what they did! ;D
It's good that GPS does what it does, reliably and accurately, and I admit that I use it extensively, but having all my navigational eggs in one electrical basket for an ocean crossing wouldn't make for a whole lot of peace of mind in my case. I do want to have a KISS method to determine where (even if only approximately) I am. I think I would like to make sights manually, and then check my sights afterwards against what the GPS says. That way I could know that I had become proficient at the non-electrical, reliable "old school" nav in case the "new school" nav went out, either because of failure on my recieving end, or because of some other reason, ie another big terrorist attack that would cause the military to scramble signals, or perhaps due to an EMP-induced failure of the system.
One thing about GPS accuracy - yes, they will tell you your position to within a few feet, *BUT* people put blind faith on what the little chart on the GPS screen shows them as to where that position is, and that is possibly seriously misplaced faith in tight quarters, in my opinion and experience. I've read and seen that the errors possible in what a chartplotting GPS displays can be as much as several hundred feet, given that 1) charts are not always accurate or up-to-date in what they show (especially charts for other parts of the world, and 2) that how the chart is scanned in to and then rendered by the GPS on its screen can induce further errors.
I've seen this myself at times, with my WAAS GPS pulling in good signals from several satellites. I have been on the ICW, dead-center of the channel, looking at a course saved from just a few days/weeks earlier that, if I followed it blindly, would have required wheels or tank treads to have been installed on my boat, since it was several hundred feet or yards off to one side of where the water actually was.
My favorite nav instruments are the good old Mark I Eyeball, and Common Sense and Reasoning. ;D
http://164.214.12.145/index/index.html
http://www.tecepe.com.br/nav/almanac.html-ssi
Here are some links someone may find usefull..sight reduction tables and natical almanac.. there are also full size pilot charts and light list ..everything in pdf format
I would think that there are hardly few boats in the 26 -30 foot size range that would have the capability to run computers 5 miles from the bottom .....unless you had a very long land line connection.even then itsa nufangled electric gizmo.computors are not infallable.when some thing goeth rongo on the one I yooz atwoik,I can make sure it never has to be fixed again with the application of relatively primitive hardware.....a sledge hammer(that should be woit some applause hmmmmmmmm?)
Quote from: starcrest on February 05, 2006, 05:49:19 PM
I would think that there are hardly few boats in the 26 -30 foot size range that would have the capability to run computers 5 miles from the bottom .....unless you had a very long land line connection.
There's a lot you can do with a laptop, by battery, that you don't need any external connection.
I use several different computer based almanac/calculators in my CN practice. Of course, I also do site reductions by hand, too (no reduction tables, crunch numbers with raw equations, either with small hand held calculator or with a slide rule).
I think I linked to several sites that offer such computerized tools higher in the thread.
Even if you need a connection to external servers, there are satellite based ISP's, or even HAM based if you have radio gear on board. I don't think this necessarily comes under the KISS principle, but the resources/capability is there if one chooses to use it.
actually I have seen those satellite dome type antennae on some large houseboats here.but I wonder how the actual hardware would stand up thru time to the ravages of the marine environment(not the artificial reef type) but the high humudity ,heat and salt air of the average small boat.I can never forget the pounding of the way north from hawaii.....man that was not fun.infact on the triton my vector loran had a problem with the lat/lon #2 button.it would not give a read out.I havent done much sailing lately but I have great gps fun with the garmin 12 in the car.the up/down/left /rite arrow button has been acting up.like any electronic gizmo it too is not infallable.half way there on the schooner I left the short wave receiver on the deck.It got ruined from the sea spray that could have been disasterous,but like magic someone produced a branspankinnu RDF that had tha ability of getting wwvh on 2.5 mhz.
http://www.marineplanner.com/bowditch/bowditch.cfm
Free open source stargazing program. Awesome!!!
Try zooming the nebulas!
http://www.stellarium.org/
You may also like Celestia, it is free as well. You can fly to the planets, add spaceships, and make great movies. I use both in my astronomy class and Celestia is as much fun as Google Earth
http://www.shatters.net/celestia/
Cool, guys, both of ya! :D
Karma pops... ;D
First a disclaimer:
I am not saying go out an make this for using on a trip! It is of interest value only. Maybe of some use for understanding basics.
end of disclaimer.
That was for StarCrest wherever he is, so when he comes back and reads this, he will not have a cow. "that does happen not just on TV " ( by the where r U dude?) ;D ;D ;D ;D
anyway found this:
http://www.tecepe.com.br/nav/CDSextantProject.htm
A couple of other things...
Tania Aebi wrote about how she had a lot of trouble using plastic sextant, and had not realized how much it had warped from sitting in the sun. The fact that it had warped was not easily apparent and the source of her problems with it. Once she switched to a metal sextant, much progress was made in celestial navigation.
A heavier sextant is often easier to aim, but more tiring to hold.
A good starfinder is worth its weight in gold...too bad they're not very heavy. ;)
A good book to get as a reference, is "The Complete On-board Celestial Navigator" by George G. Bennett. It has all the tables and forms you'll need to do celestial nav through the end of next year...I'd imagine a new version is due shortly.
Most of the better metal sextants are shipped with a little chart that gives you any index errors at various points along the scale. I consider myself fortunate that mine doesn't have any index error at all. But this can change over time.
BTW, I use an Astra IIIB. I got it on sale at Westmarine, but their prices for it are not normally the best.
If you do try to use an artificial horizon, remember that there is no dip error correction for height as the artificial horizon removes the need for it. Water is a lousy liquid for an artificial horizon—I'd use thinned molasses or soy sauce instead... especially if I was going to do sun sights.
Moon sights are a royal pain in some ways, as there are many more corrections for the moon than there are for any other celestial body. YMMV.
A few other points...
1) GPS has been shut down by the US military before...around the time of Desert Storm IIRC, and it could happen again.
2) Also, most of the GPS satellites are past their designated operating lifespan, and could fail catastrophically, like the Hughes IntelSat IV did about six years ago, and wiped out 80%+ of the paging service in the country by doing so... same thing could happen to GPS.
3) GPS and Celestial Navigation are both tools... and one is a good backup/check for the other...but the Mark I Eyeball is also pretty good...and when you're near the coast, it should also be used.
4) Just remember the little picture on the GPS isn't really a representation of where you boat is...it is a representation of where the electronic satellites are telling they think the cartographer who made the map thinks your boat should be... and some of the maps are based on data from the 1890s still... so they should be thought of as somewhat inaccurate.
Just soem food for thought. I personally think that anyone who goes on bluewater without a GPS and a sextant, and all the necessary paper books for it is crazy... :D
I like solving Navigation problems, and I'm currently working on calculator solutions to many of the problems that can be solved with the trusty old Bowditch. These are good techniques to have, imo, as all of our wonderful modern electronic gadgetry can fail.
You might say "ah, but your electronic calculator can fail, too." Yes, indeed. That's why I have a non-electronic, no-batteries needed slide rule in my nav kit. Just In Case (tm). And I'll bet I can do sight reductions by hand with the slide rule ALMOST as fast as many can do them with HO 249.
So here's a practice problem I am working out, and to keep things simple I'll make a few (ridiculous) assumptions. The set-up is a sail from Georgetown, SC to Portland, ME, long enough that we possibly don't have a single Mercator Chart with both endpoints. We are going to ignore Massachusettes and the fact that Georgetown is several miles inland from the ocean. Let's just pretend we want to sail from the lat-long of Georgetown to the lat-long of Portland over 'open' water.
Also, I'll give the lats and longs in decimal degrees (rather than degrees decimal minutes) just to make punching on the calculator a bit easier. The problem: Given initial and final Lat-Long, Require rhumb line course to steer and distance.
Georgetown: 32.22 N, 79.17 W
Portland: 43.40 N, 70.16 W
Solution:
A Mercator chart has the properties that a straight line on the chart is a constant compass course. This is not technically the shortest distance between two points on the earth (unless along a N-S line or the equator itself), but is 'easier' to steer. This course is a rhumb line.
Why don't we want to use a single small scale Mercator chart, or chain together many small ones? The problem is that for a Mercator Chart, the flat distance represented by the lat and long are not the same, and the 'ratio' of lat to long varies with distance from the equator. This is a mathematical property of the projection. If you took a chart of Georgetown and a chart of Portlant, laid them so their corners are in the 'right place' and tried to strike a rhumb line, your course would not be correct since the 'ratio' of lat to long for the two charts would be different.
To calculate the distance, we need the course first. And, it turns out, the course is harder to compute. The equation is simple looking,
C = arctan ( DLo / m )
where arctan is the arctangent function, DLo is the change in longitude and m is the meridional difference, M2 - M1. Here, the M's are the meridional parts for our two latitudes, which can be computed using:
M = 7915.704468 log ( tan ( 45 + lat/2 ) ) - 0.23268932 sin ( lat ) - 0.052500 sin^3 ( lat ) - 0.000213 sin^5 ( lat )
M is a quantification of the relationship between latitude and longitude on the projection, and it should be noted that this formula is approximate (as most are that are used in practice for computing M).
So, for the problem at hand,
M2 (Portland) = 2031.5533
M1 (Georgetown) = 2880.0139
m = M2 - M1 = 848.4606
When this m and DLo is plugged into the equation for the course to steer, we get C = N 32.5 degrees E, or 32.5 degrees True.
That notation for the course means 32.5 degrees East of North, and is necessary since the 'quadrant' of course computed is determined by how the endpoints are situated. It is similar to figuring out the azimuth quadrant in a celestial sight reduction.
With the Course in hand, it is relatively simple to compute the distance:
d = l / cos ( C )
where l is the latitude difference, L2 - L1 and C is the course we computed above. So,
d = 795.4' = 795.4 nm.
Incidentally, the Great Circle Course for this 'trip' is 794.1 nm, only about 1 mile shorter!
Okay, so why bother with all of this? Strictly speaking, we should not prick the chart to get distances (unless a fairly large scale chart) unless the course lies due E-W. This is because a minute of longitude is not only not 1 nm, but it is not constant! That's what those M's correct.
But we often don't have to compute the course to steer as we did here. The course betwen two endpoints on a Mercator Chart is an accurate rhumb line course. So, you could simply measure the angle using course protractor (or other whatever is your prefered method for laying courses on the chart) and use it in the equation for distance given above.
This is a tremendous back-up, in my opinion, against putting ALL your navigational eggs into one GPS basket. The math is not that complicated if you have the formulas written down. And even better, there are downloadable programs for pocket electronic calculators available (as well as javascript based web pages) to handle the math.
To help learn how these equations work, I am writing my own set of programs for the TI Voyage 200 calculator. The V-200 is $172, which makes it over $300 cheaper than CelestiComp ($499). I have the sight reduction, noon lat and rhumb distance programs 'done' and testing, and will post these and others for free download soon.
If anyone on the board has an older TI calculator (TI-89 or 90), I'd like to port the programs to them. Unfortunately, it is my understanding that V-200 programs are not downwardly compatible, so we'd have to recode for the older calculators.
:-[ :-\ :'(
Rhumb lines are what the GPS computes fro what we commonly call "waypoints." If you know the lat-long of the waypoints along your route, you can compute your own course-distances for each leg.
You know, if the GPS is broken.
;)
Say it isn't so... GPS's break or stop working? Please don't tell me that gadgets aren't perfect. :o ;D :D
I might have to do math?? :o I think Jimmy Buffett has a song titled Math Sucks. :)
PS- I actually enjoy Math. ;)
Even simple math makes my brain hurt.
Anybody use a nautical slide rule like this one?
http://www.weems-plath.com/cgi-bin/showCollection.cgi?categoryKey=23&subCategoryKey=36&itemNumber=105
Quote from: Cmdr Pete on July 26, 2006, 03:54:16 PM
Even simple math makes my brain hurt.
Well, with the calculator programs (either mine or somebody else's, they are out there), you simply have to enter the data. In the case of my sample problem above, you'd only have to enter the lat-long of starting and ending points.
The program does the rest. :)
Quote
Anybody use a nautical slide rule like this one?
Those are pretty good for what they are, but are essentially single-purpose. They solve the distance-time-speed equation, and that's it.
It's probably a matter of personal preference, but I try to avoid single-purpose devices. Using them not only adds space/storage issues, but it also tends to breed dependency on a specific tool for even simple tasks.
So, the GPS is broken.... must be time to use my brain again.
Seriously, GPS units are more likely to lose their signals at critical moments than "break" altogether. Everything on board can break. As serious sailors, we have to have a backup plan.
I am a sailing instructor and work mostly with cruisers. The question of what to do if GPS fails comes up every cruise. My remarks are that we start observing the circumstances that surround us. This isn't a math problem yet.
Practice on the good days as training for the not-so-good navigation days.
First. Keep track of departure times, directions, speed, etc. Draw the course and distance travelled on the chart. The process is called "ded reckoning" with the d-e-d being an abbreviation for deduced. I make a new DR fix every two hours if no course changes have occurred or every time I change course. It works very well.
Second. It is possible to estimate speed and arrival times using a couple of simple "guesstimates."
Speed... if you are really ripping along, the speed is 5 to 6 knots. A comfy sailing speed? Guess at 3 to 4 knots. Slower than that? Who cares? The speed ranges are a function of boat type. The Olson 30 racing boat I spent so many years on loafs along at 6 knots on the same day a Pearson 30 (a favorite of mine) sails briskly at 5kts. Experience will teach us about our own boats.
Time. Use this simple table that is easy to derive.
6 kts is a nautical mile in 10 minutes
5 kts... in 12 min
4 kts... in 15 min
3 kts... in 20 min
Anyway, there are a myriad of ways to navigate without GPS and breaking our brains on math. It all starts with observation. A navigators first job is to observe.
electronics help us keeep schedules. Eyeballs and brains help us go sailing.
One of the fun things about my job is doing this with new-to-cruising sailors.
In case it matters to anyone why a "big boat sailor" is here. A) I am a little boat sailor stuck in a big boat body. B) my customers ask questions discussed here. This provides me with insights into questions, thinking, and solutions.
Best,
Norman
Boston
QuoteIn case it matters to anyone why a "big boat sailor" is here. A) I am a little boat sailor stuck in a big boat body. B) my customers ask questions discussed here. This provides me with insights into questions, thinking, and solutions.
Just glad you are here Norm. Thanks ;D
Quote from: Norm on September 21, 2006, 09:06:44 AM
Time. Use this simple table that is easy to derive.
6 kts is a nautical mile in 10 minutes
5 kts... in 12 min
4 kts... in 15 min
3 kts... in 20 min
A similar useful technique I've read about and used is the 'how far in six minutes' method. You travel 1/10th your speed in kts in six minutes - 3 kts = .3 nm in 6 minutes, etc. Useful on it's own or for recreating the table above 'in your head.'
I also agree ded reckoning should ALWAYS be employed. It's better to know where you are than to have to try to figure out where you are. I don't always plot a DR position on the chart (okay, I rarely do if in pilot waters), but I do make notes of times that I pass certain features, aids, etc. I made a "log chart" that I keep with my nav tools that has columns for the following headings:
Position, Time, Speed, Course (Mag), Course (True), WX Notes, WX Forecast and General Comments.
For position, I simply write "Mark 31 200 yds to stbd," a position line from an object or a Lat Lng, etc.
There's lines for 36 entries per page.
The "problem" that began this thread was one of knowing a start position and a desired ending position (whether destination or waypoint) and computing the course and distance. For small distances, you can strike both directly off a large scale Mercator chart; for larger distances, that would give the wrong course and distance due to the mathematical nature of the projection.
getting back to the original idea... I used a gnominic chart a few years ago while planning a trip across the Pacific. Should we start talking about that?
I was trying to make the point that not all navigation is math and there are non-math workarounds. Problem is... I type so slowly.
If you strike a 'straight line' between two points on a gnomic projection, don't you get a great circle rather than a rhumb line? I've never used a gnomic chart personally.
Quote
not all navigation is math
True. I guess it might depend on how you define "math." :)
Navigation is data processing. The data is measured values - courses, speeds, time, postions (in some coordinate system), etc, and the manipulation of that data is intrinsically mathematical in nature. Of course, there's more to math than arithmethic. Plotting a position on a chart is technically math.
For example, I offer that if you are looking at a daymark and trying to determine if you are on a course to clear it, you are doing math. You may not be writing numbers on a piece of paper or punching them into a calculator, but you are processing angles and delta-angles visually. I'd say you are doing math. Others may disagree.
Maybe it's more of semantic point than one of practical value.
Quote
there are non-math workarounds
For some problems that may be true. I've never seen any kind of written material (books or on the web) that deals with navigation or pilotage that does NOT deal with mathematical problems explicitly. I know Bowditch is one of the navigator's main resources, and that book is nothing but math. Even cel nav with HO 249 requires some basic math.
Is there a way to solve all of those problems without math? I would love to learn any navigational trick there is. I am fascinated by all navigational techniques, both as theoretical problems and practical tools for my toolbox on the water.
Wouldn't the simple way to do this be to just shoot an angle on Polaris and start sailing north paralleling the coast until you get a reading of 43.40, then head due west? After all this is what sailors use to do before they had timepieces accurate enough to allow them to determine longitude.
While that would be one way to do it, it would be far longer a distance to sail, as you'd be doing the two legs of the triangle, rather than the hypotenuse.
In fact you would be sailing roughly the hypotenuse. Green represents approximate course paralleling the coast. Course based on coastal observation and angle on Polaris.
(http://i28.photobucket.com/albums/c245/pyrat/Sailing/SailingProblem.jpg)
But Joe, Cap'n Smollet said:
QuoteWe are going to ignore Massachusettes and the fact that Georgetown is several miles inland from the ocean. Let's just pretend we want to sail from the lat-long of Georgetown to the lat-long of Portland over 'open' water.
I was responding to your assertion:
Quote from: AdriftAtSea on September 24, 2006, 09:41:28 AM
While that would be one way to do it, it would be far longer a distance to sail, as you'd be doing the two legs of the triangle, rather than the hypotenuse.
The intent of the graphic was to demonstrate that I would, be sailing, roughly, the hypotenuse.
Regarding the original parameters:
QuoteWe are going to ignore Massachusetts and the fact that Georgetown is several miles inland from the ocean. Let's just pretend we want to sail from the lat-long of Georgetown to the lat-long of Portland over 'open' water.
I don't see where I would be in conflict with this basic premise. I am offshore, not using the ICW so I would not be in violation of the "open water" requirement, and I did ignore that Georgetown is inland. If you are referring to the fact that my theoretical sailing route in green went around Massachusetts, OK, it was a quickie, ignore that part of the route and just go straight. I would not be using a GPS, only something to give ma an angle on Polaris and, depending on what else you want to limit the use of either my radar or binoculars to periodically observe the coast.
Quote from: s/v Faith on September 21, 2006, 09:30:41 AM
QuoteIn case it matters to anyone why a "big boat sailor" is here. A) I am a little boat sailor stuck in a big boat body. B) my customers ask questions discussed here. This provides me with insights into questions, thinking, and solutions.
Just glad you are here Norm. Thanks ;D
Ditto. :)
Hey - we 'outed' Norm. lol ;)
As to the original post - good thinking, John, and a neat idea for the calculators. I'm one of those people who gets sleepy when
doing thinking about math, so it'll take me a while to unravel all of those sofistycated formuli up there and really understand it. :)
Right now, I'd most likely wind up doing what JoeP talks about - set a course offshore of the nearest cape, sneaking in for an observation when near it to confirm my DR, and/or nearing shore again when my sights/latitude indicate that I am close to where the destination was.
Inbetween approaching land, I'd have the GPS taken apart, as I tried to fix the cursed thing and make it work again... ;D
First Point:
I really, REALLY like JP's idea - for when it will work (which is admittedly a LOT of the time). It's a low tech solution that is time tested.
There are some caveats, though: One, you may have cloud cover and cannot get that Polaris site right when you really need it. Two, you have may to make the trip as quick as possible due to a sick or injured crew member, or some critical failure on the boat. In the SAMPLE exercise, you do have a nice coastline to follow, but what about otherwise? It could get tricky, and sailing to the lat then following it E or W could add a bit of time to the trip.
Just some thoughts to throw out there.
Second Point:
There are many places where one may wish to follow pre-selected "waypoints" without the luxury of visual aids. South Pacific reef rimmed islands come to mind, or even a poorly marked North American channel in fog. True, both are circumstances that prudence MAY demand an alternative plan.
My point in introducing this thread was to:
(a) present the underlying technique the GPS and other nav computers use to compute course and distance when you know the lat and long of your starting point and destination, NO MATTER the scale or the conditions (or whatever other technique might serve as well or better). If I chose a poor example to set up my hypothetical, please don't let that detract from the fact that knowing how to do this is a GOOD technique to learn (if for no other reason than just to build navigational confidence).
(b) to 'connect' with the navigators of the 'old days' that did stuff like this all the time, without GPS or even calculators. Like Joe Pyrat's example, the technique listed at the head of this thread has been in use on the high seas on sailing vessels for hundreds of years. If it were not really useful, I doubt it would have stuck around long enough or been deemed important enough by Nathaniel Bowditch to include in his masterful collection of PRACTICAL seamanship.
(c) to reiterate that reliance on electronics is, in my HUMBLE opinion, not the safe, prudent approach. I know of boaters that routinely go 'to sea' without paper charts aboard, don't know rule of thumb techniques and certainly don't practice cel nav. They follow the little blip on the chart plotter - that's navigation to them. I merely wanted to emphasize that using a GPS was cool, but if it DID fail, one was not LOST with the waypoints one selected to follow.
In the end, when it comes to learning new tools and techniques, we must all pick and choose which we think we will find useful and which we won't. I will post the links to the calculator programs here on sailfar (when they are done). If anyone wants them, the will be free. If not, for any reason, not-clicking a link to download a file is ALMOST as easy as clicking it. ;)
John -
As well as posting links to the software, would you consider doing up a simple tutorial for those of us here who are admittedly ignoramuses? ;D Maybe put in which calulators it'll work on, where to get them, and how to load your programs into the calculators? I like the idea of having a yet another backup method for navigation.
BTW - approx how much does one of the calculators cost?
Thanks for the expanded description of what you were posting about - I understand much better now.
Signed -
Ignoramus #1
;D
Quote from: CapnK on October 05, 2006, 10:43:29 PM
As well as posting links to the software, would you consider doing up a simple tutorial for those of us here who are admittedly ignoramuses? ;D
Absolutely. Free tech support - but only for SailFar members!. ;D ;D
Quote
Maybe put in which calulators it'll work on, where to get them, and how to load your programs into the calculators?
Right now, the code will only work on the TI-Voyage 200 (http://www.ticalc.org/basics/calculators/v200.html) (ya gotta love that name for a calculator to use on a boat, eh?). Programs written for the older TI graphing calcs (such as the very popular TI-89) will work on the V-200, but ones written just for the V-200 will not work on the older ones.
But the V-200 is an AWESOME calculator. I have been extremely impressed with it. To give a brief idea of what this puppy is, it has the same family processor as the original Macintosh desktop computers had (M68000 family). Uh, that means this little handheld calculator is roughly equivalent to one of those, but with modern software, flash memory, etc. It's a heck of a device. Well worth the money, and there are TONS of useful programs for it. I bought it in 2004 at the specific recommendation of one of my clients for the project I was doing for him, and as I say, have been impressed.
Quote
BTW - approx how much does one of the calculators cost?
The best recent price I've seen for a V-200 is $172. The Celesti-Comp runs close to $500. So, with my (or someone else's) sun/moon/planet/star epherimides, site reduction programs, and other programs like the rhumb line one discussed in this thread, you could have the rough equivalent to a Celesti-Comp for over $300 cheaper. That's what I am moving toward.
Quote
Thanks for the expanded description of what you were posting about - I understand much better now.
No problem. Actually, I saw something in one of your earlier posts,
Quote
Right now, I'd most likely wind up doing what JoeP talks about - set a course offshore of the nearest cape
that I thought would help clarify it further. How are you going to determine that course to the nearest Cape? That was the whole point of this exercise .... compute the course and distance when you know the geographical coordinates of the endpoints. If your position and the destination (your Cape) are on the same chart, you should be okay measuring it off the chart. BUT, if they lie on different charts and there is significant different in latitude between your position and the Cape, trying to get the course this way will be technically incorrect. The issue is: "Is such a course incorrect enough to cause a problem."
I meant it as just another tool, and not one to replace simpler techniques when they are adequate or appropriate.
The tutorial idea is great. Hmmm, The University of SailFar. :)
Check out this article about the effect of solar emissions on GPS.
http://www.washingtonpost.com/wp-dyn/content/article/2007/04/07/AR2007040700916.html
Oded
Key line from the story—A major electromagnetic storm at the end of October 2003, for instance, had some GPS units down for as much as 19 hours.
That's why I have a sextant, charts and other traditional navigation tools on-board. :)
Thought this important enough to lift from another site and repost here, especially for Chesapeake area sailors. The GPS coords given are for Pax River NAS, and anywhere within 35 nm may be effected.
Quote
THE GPS NAVIGATION SIGNAL MAY BE UNRELIABLE FROM 01 APR 08 - 31 OCT 08 DUE TO INTERFERENCE TESTING ON GPS FREQUENCIES USED IN SHIPBOARD NAVIGATION AND HANDHELD SYSTEMS. SYSTEMS THAT RELY ON GPS, SUCH AS E-911, AIS AND DSC, MAY BE AFFECTED WITHIN A 35 NM RADIUS OF POSITION 38-15-41N, 076-26-01W DURING THIS PERIOD. GPS USERS ARE ENCOURAGED TO REPORT ANY GPS SERVICE OUTAGES THAT THEY MAY EXPERIENCE DURING THIS TESTING VIA THE NAVIGATION INFORMATION SERVICE ( NIS) BY CALLING (703)313-5900 OR BY USING THE NAVCEN'S WEB SITE'S 'GPS REPORT A PROBLEM WORKSHEET' AT WWW.NAVCEN.USCG.GOV"
That is really interesting...I had my GPS go haywire last November at Baca Grande in SW Florida. Suddenly showed us out in the Gulf when we were almost to Burnt Store Marina. It was a charter, and the charter company just shrugged their shoulders and said "sunspots".
After the crew settled down, we did got out the paper charts and did a fix on a couple of buoys and vola', we made it home ;D.
All the more reason to learn the old ways to navigate.
This topic has been around for a while, and these concerns are nothing new.
Anyone with any knowledge of or background in electronics knows that things CAN and DO fail.
Here is a story published in the 'Guardian' titled
GPS system 'close to breakdown': Network of satellites could begin to fail as early as 2010 (http://www.guardian.co.uk/technology/2009/may/19/gps-close-to-breakdown)
Just posting it here as a reminder not to grow too attached to these miracle navigation aids.
Here is a short excerpt from the article in case the link goes dead;
QuoteIt has become one of the staples of modern, hi-tech life: using satellite navigation tools built into your car or mobile phone to find your way from A to B. But experts have warned that the system may be close to breakdown.
US government officials are concerned that the quality of the Global Positioning System (GPS) could begin to deteriorate as early as next year, resulting in regular blackouts and failures – or even dishing out inaccurate directions to millions of people worldwide.
The warning centres on the network of GPS satellites that constantly orbit the planet and beam signals back to the ground that help pinpoint your position on the Earth's surface.
The satellites are overseen by the US Air Force, which has maintained the GPS network since the early 1990s. According to a study by the US government accountability office (GAO), mismanagement and a lack of investment means that some of the crucial GPS satellites could begin to fail as early as next year....
Oh noes, you mean the miracle of GPS is not transcendental?
Ok
By the way, I'm getting $75 a head teaching celestial to those that realize this basic fact.
GPS is more reliable that the old way for me. I find that in the morning and at dusk and at high noon the GPS is off 50 to 100 feet. The water changes to much to relly on it 100%. You need to know both.
Other things can cause problems as well.
Taking it a step further, a recent circumnavigator used absolutely NOTHING. No compass, no charts, nothing, EXCEPT the stars... It helped, I'm sure, that he was/is an astronomy professor.
::shrug:: I've been doing a touch of reading on the various current and developing satellite navigation systems. GPS3 is running behind schedule, but you know - there is already one other system that's also being renovated and upgraded, and is expected to be back to 100% functionality by the end of this year (http://en.rian.ru/russia/20081229/119210306.html): GLONASS (http://www.glonass-ianc.rsa.ru/pls/htmldb/f?p=202:1:16827457493506720876). That's the old Russian built system, now part of a new Indian/Russian space alliance system. France's DORIS (http://ids.cls.fr/) system is still available, but it's accuracy is less than the current GPS and I'm not aware of any retail-level receivers.
Plus there are at least two new systems building out, the EU's Galileo (http://www.esa.int/esaNA/galileo.html) and China's Compass (http://www.sinodefence.com/space/spacecraft/beidou2.asp), both of which are expected to be operational by 2013 (Compass will begin as regionally operative, with full global build-out by 2020.) India, South Korea, and Japan also have domestic systems in development.
So, I expect satellite nav systems are a stable and permanent element of marine navigation.
There plans available online to build your own GLONASS/GPS receiver (http://www.s5tech.net/s53mv/navsats/theory.html) (2 (http://hackaday.com/2007/10/04/build-your-own-gps-and-glonass-receiver/)), and at least one company has a commercial offering (http://pro.magellangps.com/en/products/product.asp?PRODID=77). Galileo has been deliberately designed to allow current GPS receivers to use it's open signal's dramatically greater accuracy (<1m). My personal opinion is multi-system receivers will become the norm from manufacturers sometime after 2010, but in a roll-out designed to make all the current receivers obsolete of course.
It's certainly possible to sail anywhere without any form of satellite navigation, and sailors would likely be better navigators for the experience. But not because the satellite's are going to go away, or even be at risk of going away.
That doesn't surprise me. I did 2 joint tours with the Air Farce in the 60's. They couldn't fix anything or do anything right then either. TJim
Today is to be the day LORAN is turned off forever.
just saw this link on another forum today. Thought you might like the article.
http://news.bbc.co.uk/2/hi/science/nature/8494225.stm
Kinda sad in a way to see Loran go. It makes me wonder if any of us will see the last day of GPS when the Next Big Thing takes over and IT is no longer maintained/deemed 'useful.'
Interesting that it comes this week. Just two days ago, I was chatting with a friend here who, with her husband and now 15 year old son, have traveled the world by 'small boat' (a Nicholson 31). They've crossed the Canal several times, been to NZ, through the Pac, across the Atlantic, etc.
That's just background, though..the interesting (and on-topic) part of the story was their 300-ish mile circle on the Amazon in the Belem region. There were, of course, no channel markers and what charts there were were woefully out of date.
How did they navigate?
Well, you could only sail a couple of hours each day before the adverse current took over. When that happened, they anchored. The rest of the day was spent 'charting' the next day's route with the dinghy - and a sounding pole.
"How did you mark your turns?" says I. "Did you drop buoys? Or, did you have a handheld GPS you marked waypoints in?"
"No, we had none of that," came her South African reply.
"Oh, I get it; you got an eyeball on that tree, that shack over there...is that it?"
"Oh yes. That's exactly what we did. We noted what we could see when we needed to make a turn."
Eyeball pilotage - still reliable after a couple thousand years of sea navigation and, I assume, it will remain so for a couple thousand more.
(I'm trying to get her to join SailFar to share some more of their nearly 20 years of experiences in the Sailing Stories section....)
They're also called ranges, and very common in many harbors.
No, she was not talking about ranges.
She was talking about cross bearings. Looking at multiple objects on shore and recording bearings.
There were no aids to navigation - no pilings, no man-made aids at all.
And the actual channel was very different from that shown on the chart.
How would ranges help in a situation where the bottom shifted constantly? What is a range today won't be next week.
They literally felt their way forward with the dingy and recorded cross bearings at the turns. Just like the old square riggers used to do when charts were unreliable.
I thought it was cool.
The other thing she mentioned was "waiting for a local to come by on his canoe" and asking him where the bottom is today.
Kudos to the South Africans for navigating into uncharted waters.
I'm sure we all use similar techniques in everyday sailing--lining things up. This can be especially useful when compensating for current. If you're on the right course, you can line up two objects (say a buoy ahead and an object behind it on land) and keep them in line.
Or else I might just keep looking ahead and behind, keeping the next buoy on my bow and the last buoy on my stern. Simple eyeball navigation.
Reminds me of a time years ago. I had navigated down a narrow unmarked channel to a little village. I was talking to an old-timer at the dock about how I was going to sail a reciprical course back out. He tells me "See that island out there with the big clump of trees? You keep them trees on your bow and this dock on your stern."
A fairly typical way to navigate.
I won't be going to the Amazon until they get buoys and SeaTow.
Sometimes I'll use my little boat as a research and exploration vessel for my big boat. I use a handheld depthsounder to find the deep water for a future trip with the big boat. I should probably use a pole instead, since I can't get a reading off the depthsounder half the time.
Quote from: Cmdr Pete on February 11, 2010, 02:56:53 PM
I use a handheld depthsounder to find the deep water for a future trip with the big boat. I should probably use a pole instead, since I can't get a reading off the depthsounder half the time.
LOL. The ONE thing she said she would not leave without 'next time' is a depth sounder for the dink. The pole got very old.
I still like Charlie and Laura's fishing pole/float method. The float is tied on at the "no go" depth with a weight on the end heavy enough to pull the float under. If she floats, the water is less than the "no go" depth - if it sinks, you are good to go.
I HAVE used a pole (my boat hook actually) to sound a channel from the dingy ... but I was already aground and wanted to find the way out. :P
Back to the original posting. I was talking to a military satellite specialist the other day. I asked him did he ever see the GPS system go wacko. He laughed and said- "those civilian things you use? I've seen them inaccurate due to cloud cover" I thought that was interesting that we depend on them to land planes in cloud cover....
I have a friend who built his own air plane, nice two seat-er. He put a gps in it, the main diff. is in the antenna (or reciever) and of course the computer. The more you pay the better the receiver. I would imagine a $1,000 unit is going to give better service than a $100 unit. Melvin
What about the ones we use for our boats? Are the expensive ones using the military Algorithm? I bet not. Just food for thought. BTW- that makes sense about the planes. It seems that whenever our pilot goes through the fog with one that the landing is kinda rough, but it just might be my imagination.
Sorry guys nothing is 100% safe. Sometimes instruments and human judgment just malfunction. As things go gps are only a tool among many that any sailor or pilot has at his disposal. Don't sweat the what ifs and enjoy the what ises(new word of the week ISES).
I've got a sextant, and I use it but...
Three days of this day and night, closing a rocky coast from an ocean crossing, and there's gale forecast thrown in for good measure then it's ...
"I love you Mrs Garmin".. :D :D :D
(http://i279.photobucket.com/albums/kk136/highandry_photos/lacorunacopy024.jpg)
I agree- navigation is everything from looking out of the cockpit to getting a GPS fix. In reality the question should be "Should you rely on any one source of navigation information??" Heck, I am thinking about getting a cheap AM radio with a directional antenna. I am glad that we have GPS's today, but perhaps the name of the game should be how many ways can I navigate to the port?
I just received a Freiberger sextant. ;D
(http://landandseacollection.com/sitebuildercontent/sitebuilderpictures/freiberger79bwincse003.jpg)
What a wonderful gift! I will probably be selling one of my Davis sextants soon.
Nice looking, Craig! Is that an aluminum frame/body?
Quote from: s/v Faith on June 19, 2010, 11:13:01 PM
What a wonderful gift! I will probably be selling one of my Davis sextants soon.
Which model Davis are you going to sell?
Nice score, btw. :)