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Old 14-01-2016, 10:46   #31
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Re: What happens when your navigation systems fails

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Originally Posted by adlib2 View Post
I read some years ago that the USN eliminated celestial navigation from their Officers training.
It has returned

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Maritime nostalgia, however, isn't behind the return.

Rather, it's the escalating threat of cyber attacks that has led the Navy to dust off its tools to measure the angles of stars.

After all, you can't hack a sextant.
Seeing stars again: Naval Academy reinstates celestial navigation - Capital Gazette
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Old 14-01-2016, 11:04   #32
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Re: What happens when your navigation systems fails

All the GPS units on those boats did not suddenly malfunction. That's just silly to even trot out. We'll probably never know what happened but there are lots of explanations that make more sense than GPS receiver malfunction. One thing that comes to mind is that all the units were set with the wrong datum. That would do it and it would be pretty dumb if that's what happened. Jamming by the Iranians is a possibility. Heck, jamming by the US or some other power in those waters is possible and these guys got caught in "friendly fire".

But this is a terrible example to use for promotion of casual sextant learning. That is so 60's.
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Old 14-01-2016, 11:11   #33
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Re: What happens when your navigation systems fails

I'm sure there is more to this than we will ever know
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Old 14-01-2016, 11:15   #34
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Re: What happens when your navigation systems fails

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But this is a terrible example to use for promotion of casual sextant learning. That is so 60's.
My first GPS was 1992. I learned coastal navigation in 1980's. I still use paper, plotters, dividers, and compasses for coastal navigation (unless I am teaching electronic navigation). My sextant comment was meant to humorous

Offshore I have been renewing my celestial skills as a means of whiling away the time. (Long periods of tedium ... )

There are other approaches those naval vesssels could have used: following depth contours, dead reckoning, radar (using a VRM), etc..
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Old 14-01-2016, 11:16   #35
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Re: What happens when your navigation systems fails

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I'm sure there is more to this than we will ever know
Are you implying that military witholds information. Well, who knew?
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Old 14-01-2016, 11:23   #36
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Re: What happens when your navigation systems fails

Military GPS is encrypted, difficult to impossible to spoof.
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Old 14-01-2016, 11:30   #37
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Re: What happens when your navigation systems fails

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Military GPS is encrypted, difficult to impossible to spoof.

And now the Iranians have some encrypted receivers to play with.

GPS is easy to jam.
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Old 14-01-2016, 11:50   #38
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pirate Re: What happens when your navigation systems fails

The GDUBBYA School of Navigation...
Comes straight after the Geography course..
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Old 14-01-2016, 12:14   #39
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Re: What happens when your navigation systems fails

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There are other approaches those naval vesssels could have used: following depth contours, dead reckoning, radar (using a VRM), etc..

I take it you have not looked at a chart of the area?

- The depth contour is quite flat 160-180, until you get very close to the islands.

- The islands are very low and they were most probably out of (small boat) radar range


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as an aside, there are random direction current eddies of about .2 kts this time of year in the gulf.

your suggestions might be appropriate if they had actually hit these island, or even come close to hitting them. . . but they did not. They just came close to a 12nm boundary line, and neither a radar nor a bottom contour can see political boundary lines.
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Old 14-01-2016, 12:21   #40
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Re: What happens when your navigation systems fails

Many years ago before GPS there was SatNav. It was way too expensive for the typical cruiser and only the gold platers had it. One boat equipped with SatNav was transiting the Tuamotus when the electronic nav. system showed him 50 or so miles off his DR position. The skipper naturally assumed his DR was off and went with the SatNav position. Fortunately they maintained a watch and saw the island they were about to T bone because of the erroneous electronic position. Their DR position had been correct. Don't know whether they used a Celestial 'Fix' to plot the DR position or it came from the SatNav before it went wacky..

Lesson is don't blindly follow electronic navigation. Best to have back up GPS and have more than one up and running at all times and keep a running DR on paper.

Celestial is not a be all and end all for navigation. It is inherently inaccurate, subject to atmospheric shut down and the fix is only good for when you take it usually at noon, dawn or dusk. It is still the only reasonably universal way to navigate if there should be a GPS failure. My motto in the good old days of sextant and DR navigation was "We were always lost, it was just a matter of how lost." Without a triangulated fix off a known land object, we could easily be miles off our celestial fix position. That was good enough to get us around the Pacific but always subject to user error or overcast and inherent system inaccuracy. Was away from sailing for a number of years when GPS became available. First passage with GPS and I was amazed that I could look at the little screen and see exactly where we were and verify the DR instantly. I was blown away by it's accuracy. Very easy to get lulled into into complacency when you are following the magic Magenta line on your plotter.

Would be willing to bet the Navy boats had a GPS malfunction on the lead boat and the wing man didn't think to look at their GPS, the GPS was jammed/spoofed, or they had a mechanical issue and got tunnel vision trying to fix the mechanical problem and drifted into Iranian waters. IIRC their have been a number of disputed intrusions into Iranian claimed waters by US ships over the years. Seems Iranian and US Navy GPS's don't always agree. Looks like in this case, the boats actually were in Iranian Waters or we'd have heard a denial by the Navy of the Iranian position by now.
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Old 14-01-2016, 12:27   #41
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Re: What happens when your navigation systems fails

Well one can always Dead Reckon, or perhaps wreck and become dead.

Once I went fishing near the Coronado Islands, off of Tijuana, in a 22 foot power boat, long before the days of GPS, and the fog rolled in rapidly so we lost all visibility and the compass became confused as there apparently was a local geological magnetic anomaly so we had no means of knowing which way to head back to San Diego except that I recalled the general direction that the swells were coming from and so we used the waves as directional guides and headed back towards San Diego on a rough course. As we came closer to San Diego the fog lifted and also the compass regained its true bearings so we were able to progress by compass and visually. Managed to not get run down by ships but did hear them nearby and incurred their wake.

I recall the return to port as a Coast Guard cutter was headed out of the harbor at rapid speed when we entered San Diego's harbor, its wake capsized one boat and swamped another boat near us and it spun our boat about 360 degrees. Much cursing occurred on the radio and the large cutter had to stop and return to deal with the mess they had caused. Not sure what the urgency was that they felt the need to operate in the channel at near maximum speed and endanger the small craft they were passing by. But what ever it was they were delayed in responding because they caused an emergency with their inappropriate wake forming. The harbor master was less than pleased with the Coasties that day, berating them on the radio. A SNAFU of the first degree.
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Old 14-01-2016, 12:48   #42
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Re: What happens when your navigation systems fails

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And now the Iranians have some encrypted receivers to play with.

GPS is easy to jam.

Yes, but it's not the receiver that is the trick, it's the secure "fill", so they didn't get much, I'm sure all secure systems were "zeroized". If you flipped the master zeroize switch on a AH-64D it was a class A accident as you did more than a million dollars of damage as several circuit cards were physically damaged.
And yes GPS is very easy to Jam, it is a very low power signal.
I don't know if this is true but I was told Military receivers used (P) code if they had the secure fill, and (C) code if they didn't.
The military GPS signal is a completely different freq and penetrated foliage etc much better, and back then wasn't susceptible to selected availability.
Military receiver even back then with a secure fill was very accurate
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Old 14-01-2016, 12:55   #43
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Re: What happens when your navigation systems fails

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Originally Posted by estarzinger View Post
I take it you have not looked at a chart of the area?

- The depth contour is quite flat 160-180, until you get very close to the islands.

- The islands are very low and they were most probably out of (small boat) radar range


Attachment 116745

as an aside, there are random direction current eddies of about .2 kts this time of year in the gulf.

your suggestions might be appropriate if they had actually hit these island, or even come close to hitting them. . . but they did not. They just came close to a 12nm boundary line, and neither a radar nor a bottom contour can see political boundary lines.
Thanks
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Old 14-01-2016, 13:02   #44
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Re: What happens when your navigation systems fails

These patrol boats are interesting craft . . . .https://en.wikipedia.org/wiki/CB90-c..._assault_craft

waterjet drive with 40kt speed.

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Old 14-01-2016, 13:08   #45
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Re: What happens when your navigation systems fails

Does anyone really believe it was a navigation failure? An engine failure maybe, but they were where they intended to be.
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