Considering these ideas of navigation.. What is your opnion on it?

[Jim Cate]

Originally Posted by captmikem

Up till then GPS for much of the world was often no better than celestial.

I do not think you have a good grasp of celestial navigation.

GPS degraded signal, "selective availability" as it was called gave an instant fix that was typically accurate to within 100 meters, Every second of every hour of every day.

Near Shore DGPS corrected the signal to within a meter.

At dawn and dusk on a clear day/night, 30 minutes to an hour spent shooting and working out star sights will give a good navigator ONE fix. Possibly accurate to within a quarter mile (maybe an 8th mile on a calm night).

M[/QUOTE]
And that sort of accuracy is never available from the low deck of a small yacht. With the low height of eye and a lot of motion, getting within a mile is damn good!

From the bridge height of a ship, one with a steady and predictable motion, a really good navo might achieve the sort of accuracy Mike is quoting, not so likely in our world.

But, celestial navigation is, even from a yacht, good enough to make successful voyags and landfalls... lots of us did so in the "good old days". When "sat nav" became available, with its half-mile accuracy and fixes every few hours, it was a great boon, and GPS, even when the constellations were incomplete and SA was in use, we thought we'd died and gone to heaven... it was that much better.


So, I gotta agree with Mike in that you don't seem to know much about either Selective Availability or Celestial navigation!

Jim

[fernandosmooth]

Thanks everyone for the replies. I am observing all the important aspects of every post. I need to read again multiple times to make sure but I will.


So decisions were made, yesterday I bought a book mentioned here called "Emergency navigation", it was mentioned in a post. I have plans now to buy a long-term almanac and a cheap sextant to practice.


Use DR and other things. I will read again this thread now. Any other ideas, post and I will observe it!

[fernandosmooth]

Twice mentioned was Capt.Ron but I believe Captain.Bob is the better man.

https://www.youtube.com/watch?v=YrbY4hsNh64

(read my serious post above so you dont think this is my actual reply to all your ideas.)

[14murs14]

If you want to learn celestial navigation because it's an interesting historical skill or because you like the math and the physics or you just find it fascinating than by all means do it. As a cadet at the Coast Guard Academy they made us learn it because...what if (at the time) GPS and Satnav and LORAN and RDF all independently failed at once and there were no other ships on the sea or airplanes in the air whose attention you could get, what would you do then cadet!? Which was utter BS then and even more BS now. For a trivial amount you could buy a dozen independent devices with GPS receivers, heck without trying I have 10 independent GPS receivers on my boat, none of which is any more susceptible to lightening (Faraday cages, seriously asks this electrical engineer?) or any other failure than the watch or radio receiver you need for celestial. The GPS constellation isn't "going down", if you truly believe that you'd never get on an airplane flying in instrument flight conditions since GPS is approved as the sole navigation source for both en-route and approach phases of navigation where far more precision is needed than you'll ever require at sea. You're seriously more likely to be hit by blue ice falling off an airplane or a meteor than starving to death due to not knowing celestial navigation!
That said, when I start my retirement cruising I'll probably go buy a sextant and the tables and relearn (or in my case really learn for the first time) how to do it because it is a cool thing on a number of levels. It's just a shame that I was so turned off of it at the time I could have first learned it by a bunch of ridiculous BS about it being a crucial skill. So don't be that person who turns people off to something cool by throwing out a bunch of crap about how you somehow aren't a prudent navigator if you aren't proficient in celestial nav, please!

[hpeer]

Just a smart ass answer, but a Steel boat.
Instant Faraday cage
When you hit you just go clunk and push off

[fernandosmooth]

Originally Posted by stewie

You can use a portable radio as an RDF. For example find a medium wave radio station on say Barbados. Turn the radio to the null ( most inaudible) position and that is the direction of the radio station.

Could someone explain me this? I was reading on RDF just now but I am unable to see a normal radio doing this. So I turn the volume down and..

[StuM]

Originally Posted by fernandosmooth

Could someone explain me this? I was reading on RDF just now but I am unable to see a normal radio doing this. So I turn the volume down and..

No, you don't "turn the volume down".

You turn the portable radio around physically until you get the lowest /highest volumes.


A typical MW portable radio has an internal ferrite rod antenna which is at the top and parallel to the face of the radio.This antenna is quite directional.



When the signal is strongest, the face of the radio is either pointing directly to or directly away from the transmitter. When the signal is weakest, the antenna is pointing either directly to or directly away from the transmitter. You will need more info to determine which of the two possible directions is towards the transmitter, but that is usually fairly obviously from your DR position.

[fernandosmooth]

Makes a lot more sense now. Thanks. I will try this today.

[valhalla360]

Originally Posted by 14murs14

If you want to learn celestial navigation because it's an interesting historical skill or because you like the math and the physics or you just find it fascinating than by all means do it. As a cadet at the Coast Guard Academy they made us learn it because...what if (at the time) GPS and Satnav and LORAN and RDF all independently failed at once and there were no other ships on the sea or airplanes in the air whose attention you could get, what would you do then cadet!? Which was utter BS then and even more BS now. For a trivial amount you could buy a dozen independent devices with GPS receivers, heck without trying I have 10 independent GPS receivers on my boat, none of which is any more susceptible to lightening (Faraday cages, seriously asks this electrical engineer?) or any other failure than the watch or radio receiver you need for celestial. The GPS constellation isn't "going down", if you truly believe that you'd never get on an airplane flying in instrument flight conditions since GPS is approved as the sole navigation source for both en-route and approach phases of navigation where far more precision is needed than you'll ever require at sea. You're seriously more likely to be hit by blue ice falling off an airplane or a meteor than starving to death due to not knowing celestial navigation!
That said, when I start my retirement cruising I'll probably go buy a sextant and the tables and relearn (or in my case really learn for the first time) how to do it because it is a cool thing on a number of levels. It's just a shame that I was so turned off of it at the time I could have first learned it by a bunch of ridiculous BS about it being a crucial skill. So don't be that person who turns people off to something cool by throwing out a bunch of crap about how you somehow aren't a prudent navigator if you aren't proficient in celestial nav, please!

This is basically what I was going to post...
- if you find it fun and interesting, go for it.
- if you are really worried about being lost at sea, there are lots of better things you can do that have higher odds of being helpful.

PS: Just watched a cool documentary on youtube about the search for longitude.

[belizesailor]

Celestial Nav is a gratifying skill to master, but the odds of really needing it today are slim. This is especially true given that multiple countries have launched GPS satellites and chipsets are readily available that receive from multiple country's systems (even my cell phone has such a chip set). The odds of all your GPS devices failing and/or all country's signals going dark all at the same time are very slim. A lightening stike might take out all your devices though.

I did actually need celestial nav once back in the days of "selective availabilty". We were crossing from Mass. to Bermuda. About half way across the GPS signal went away...totally gone...we had several GPS's aboard and none had signal. Fortunately we had been practicing celestial and plotting our fixes vs GPS to see how we were doing. We navigated the rest of the way to Bermuda using celestial and DR. It was very satisfying to make successful landfall this way (Bermuda is pretty easy to miss).

Once ashore we learned why the signal went away...Operation Dessert Storm!

I have a Pacific crossing coming up next year and am seriously considering taking my sextant along to brush up my now VERY rusty celestial skills.

[Delfin]

Originally Posted by Gypsyjon

Are you all aware that Trump is considering shutting down all our atomic clocks?


https://www.voanews.com/a/time-may-b...s/4554376.html

Not quite. There are around 20 of them in the US alone. This just pertains to the WWV signals that use a cesium clock in CO, which shouldn't be shut down, IMO.

[14murs14]

Originally Posted by belizesailor

Celestial Nav is a gratifying skill to master, but the odds of really needing it today are slim. This is especially true given that multiple countries have launched GPS satellites and chipsets are readily available that receive from multiple country's systems (even my cell phone has such a chip set). The odds of all your GPS devices failing and/or all country's signals going dark all at the same time are very slim. A lightening stike might take out all your devices though.

I did actually need celestial nav once back in the days of "selective availabilty". We were crossing from Mass. to Bermuda. About half way across the GPS signal went away...totally gone...we had several GPS's aboard and none had signal. Fortunately we had been practicing celestial and plotting our fixes vs GPS to see how we were doing. We navigated the rest of the way to Bermuda using celestial and DR. It was very satisfying to make successful landfall this way (Bermuda is pretty easy to miss).

Once ashore we learned why the signal went away...Operation Dessert Storm!

I have a Pacific crossing coming up next year and am seriously considering taking my sextant along to brush up my now VERY rusty celestial skills.

I don't doubt your loss of the signal and cool story of using celestial. I would point out that GPS was not turned off during Dessert Storm, in fact selective availability, which was a purposely induced error in the GPS signal, was actually turned off during Dessert Storm which made everyone's commercial GPS signals more accurate, not less. This was because coalition troops had lots of commercial GPS receivers and not enough of the coded ones, or the code update infrastructure, and the Iraqi troops had no GPS receivers to speak of so it made sense to make it more accurate rather than turn it off (https://books.google.com/books?id=Kg...6AEwDnoECAQQAQ)

Note: "selective availability" didn't mean they made the GPS signal selectively available, it meant that they purposely induced a small error and you needed a code do eliminate that error. It was permanently turned off in 2000 (https://www.faa.gov/about/office_org.../availability/). Also, an interesting concept we don't have to worry much about in boats is the dynamic error of a GPS signal. If we have a DGPS signal that updates once a minute it's fine for our navigation purposes. On the other hand, even if the DGPS gives millimeter accuracy once a minute it's not very useful to a missile or even a fast aircraft that's covered many miles during that time.

[belizesailor]

Yes, I understand SA...the event was just during that era. I have no official proof the civilian signal was turned off or degraded, but none of the GPS units aboard (two fixed mounts plus most crew had portables), were able to receive a signal.

All units resumed normal operation a few days later.

Given the concurrent timing with a major military event we assumed they were related.

[14murs14]

Originally Posted by belizesailor

Yes, I understand SA...the event was just during that era. I have no official proof the civilian signal was turned off or degraded, but none of the GPS units aboard (two fixed mounts plus most crew had portables), were able to receive a signal.

All units resumed normal operation a few days later.

Given the concurrent timing with a major military event we assumed they were related.

Actually I was chatting with someone about this and learned something new. Apparently they actually changed the orbit of several of the GPS satellites, which weren't as robust of a constellation as we have now, in order to ensure coverage over the middle east. It stands to reason that doing this would result in gaps elsewhere, probably right where you happened to be! Thanks for the story, made me learn something.

[SteveG58]

Using a plumb bob on a board marked out with a protractor can give you a fairly accurate reading. Midday only I think!