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Old 13-01-2016, 21:17   #16
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Re: What happens when your navigation systems fails

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Originally Posted by blewett_john View Post
You use a paper chart, plotting paper, and a sextant.
+1

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Old 14-01-2016, 06:11   #17
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Re: What happens when your navigation systems fails

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I'm not a conspiracy theorist but the Iranians definitely have the technology to "spoof" GPS and cause a plotter to think it is somewhere other than where it really is. It's possible they got tired of these guys constantly going by their island just 50 yards outside the limits. A little GPS spoofing could have lured them into the no-go zone and created an incident just like this.

I seriously doubt that all the GPS units on 2 boats stopped working at the same time...
Spoofing is more difficult than jamming, especially the military channels.

But only the GPS on the lead boat would have to fail or be in error, the second was probably blindly keeping station on the first.

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Old 14-01-2016, 06:22   #18
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Re: What happens when your navigation systems fails

All this celestial nav talk is hot air in this thread. These guys would have been running coastal, possibly at a fair speed. Nobody uses celestial nav in that situation.

Paper charts yes, pilotage yes, pilotage using a sextant for horizontal bearing, yes possibly maybe. Real life accuracy of better than 50 metres, on a moving platform: never!

If you are running a hostile border at 50m distance, or 100 or 250m, you would be "relying" on GPS to keep you on the friendly, or less hostile, side.
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Old 14-01-2016, 06:36   #19
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Re: What happens when your navigation systems fails

i don't know which thread is worse, this one or the one on SA.
armchair admirality at it's finest
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Old 14-01-2016, 07:18   #20
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Re: What happens when your navigation systems fails

This is just a bad example for jackdale to make his case.

First, if you believe the story that all their navigation equipment broke . . . then I have a bridge to sell you. That is always the time worn story when governments want to 'explain' something like this. Most likely, they just simply did not leave enough margin of error in their route planning, and then perhaps (or perhaps not) a fuel pump or something broke, and then the iranian's called them on it.

Second, these (very small) naval vessels were running across the persian gulf, out of sight of land. One would guess that the island (Jazīreh-ye Farsi - Farsi Island) was over the horizon of their small boat radars but in range of the iranian Navel base radars. And the island they got 'too close to' is small with very low elevation, and the visibility in this area can be quite low/short (sand in the air, and heat mirages) So a paper chart and compass probably would not have been all that much use to them in this particular situation.

Third, sextants . . . you guys do remember that from a small boat at sea they don't give you the meter (or even kilometer) accuracy of GPS - right? And you remember that in day light you need a several hour running fix (except in particular situations) to get any sort of position - right? So, no, probably not much help here.

As an aside - spoofing - it's the reason that DARPA focused on developing very small inertial navigation chips (which Dockhead and I were discussing on the autopilot thread). They primarily use internal solid state 'gyros' which cannot be spoofed. I doubt these patrol vessels had been fitted yet, but that is where the drones and cruise missiles are at today.

I am all for upping the navigation skills and knowledge of the cruising fleet, but this is just not a very credible example to make that case.
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Old 14-01-2016, 08:07   #21
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Re: What happens when your navigation systems fails

Does anyone know if Garmin chart plotters, for example, need three satellites? When I was on approach to Nassau, mine gave the message "cannot acquire satellites" after working fine on the crossing from Lucaya. I pulled out a handheld Garmin and it was happy to give me a lat and long on 2 satellites. Interesting, I mentioned this to someone else here who had exactly the same thing happen to him. Maybe this is just a dead spot in the network ...?
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Old 14-01-2016, 08:08   #22
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Re: What happens when your navigation systems fails

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Originally Posted by Littlechay View Post
All this celestial nav talk is hot air in this thread. These guys would have been running coastal, possibly at a fair speed. Nobody uses celestial nav in that situation.

Paper charts yes, pilotage yes, pilotage using a sextant for horizontal bearing, yes possibly maybe. Real life accuracy of better than 50 metres, on a moving platform: never!

If you are running a hostile border at 50m distance, or 100 or 250m, you would be "relying" on GPS to keep you on the friendly, or less hostile, side.
Firstly, why these boats would have been traveling within 50 meters (assuming that is what you meant with the figure "50m") of the boundary with a hostile country escapes me unless they were attempting to "make a statement" concerning the right of free navigation which they evidently were not. Especially so, considering that the Iranian's have a rather "flexible" definition of what constitutes their territorial waters, not unlike Qaddafi's flexible boundaries off Libya until the US Navy put paid to that policy.

Beyond the foregoing, the most recent news I have read did not speak of a navigation system failure per se but rather the greater likelihood of a "fat finger" error by a crewman when the leading boat's GPS way points were entered in their GPS system. This I have seen before on recreational boats and have heard of with military vessels.

In either case--system failure or fat finger error--the situation does seem to validate the merit of maintaining a plot on a paper chart when making a transit. While we do not do so in home waters, where we are familiar with marks and reference points, we do whenever we're traveling off shore or near shore when out of home waters. The advantage of a running plot is quite obvious if one's electronic navigation system goes down. It is less obvious, but no less advantageous, if one's navigation system is giving one erroneous data/positions. For example, in our case we plot a running fix hourly or whenever we make a course change. From each fix we project a a DR position for the next fix based upon our course and speed (which is usually in the 6 to 8 kn range). If, at that time, our GPS were to give us a position much afield of where we expect to be, and particularly so if the set and drift of the sea and potential leeway could not explain the difference given the short distance traveled since the prior running fix, I would be more inclined to distrust the data from the GPS then our DR. Despite the faith placed in them, GPS plotters are not infallible, nor immune from "spoofing" where proximity to a hostile power might be involved. Our supposedly 6 meter or better accuracy plotters have shown us ashore one to many times as we have breasted passes for me to believe in their infallibility.

FWIW...
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Old 14-01-2016, 08:33   #23
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Re: What happens when your navigation systems fails

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if (all of) one's electronic navigation system goes down.
if (all of) one's navigation system is giving one erroneous data/positions.
I don't believe either of those things happen in this case. Both are reasonably unlikely.

Most likely case . . . . (1) their planned route was 'close-ish' to the edge of 'territorial waters' of these islands. And that is not totally dumb - there is a lot of stuff in the persian gulf. We like to 'exercise our free transit rights', and it would be annoying to give everything (say) a 10nm extra clearance. (2) One of the vessels had a mechanical problem and stopped in the water (fuel pump or such). (3) the Iranians would have (probably have many times in the past) let them transit at that range, but it was 'very suspicious' when they stopped in the water, and the Iranians went out to investigate, and then 'detained' the sailors.

The lesson . . . if there is one . . . is to think about your planned clearances from 'hazards', and in that planning to account for various failures and screw-ups, and 'political hazards'.

You have to give the Navy boys some amount of credit here - at least they did not actually run into the island, unlike the pro vestas wind guys, and some other Navy incidents.

Probably we will never ever know the 'real story'. It is in no-ones interest to reveal it.

As an aside . . . when thinking about paper chart plots . . . you might want to take a look at a persian gulf scale chart - like one you might have been using for this transit. You will note that this island is just a dot, among a number of other dots (mostly oil rigs). It does not particularly stand out as requiring much more clearance than the other dots. If you plotted cross a series of much lower scale charts, you might be more drawn to the island details, but then you introduce the possible errors moving from sheet to sheet. I don't think this had anything at all to do with this incident. I think the sailors knew full well where the island was and what it was. But it is something to keep in mind when talking about paper plots.
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Old 14-01-2016, 09:52   #24
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Re: What happens when your navigation systems fails

Simple. I have a sounder, a paper chart, and a bearing compass. If the sounder's gone, I have a leadline. I also have the current almanac, an accurate timepiece and a few sextants. None of which are convenient, but all of which can get me home.
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Old 14-01-2016, 09:53   #25
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Re: What happens when your navigation systems fails

Hm... I seem to recall that the Iranians "spoofed" a US surveillance drone a few years ago, dragged it into Iranian air space, landed it and dissected it? The speedy release of the crew of these gunboats might indicate that the Iranians were just cocking a snoot at the US to make a point, the same point made long ago, before the birth of Mohamed, in Matthew 26:52? That would be a delicious irony :-)

What would Ian Fleming make of this I wonder?

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Old 14-01-2016, 09:57   #26
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Re: What happens when your navigation systems fails

Chartplotters have a tendency to make us lazy.

When using a decade old garmin etrex ($99 at walmart when new) I enter waypoints not just for where I want to go...but also places to avoid. A waypoint on a shoal or rock, and I can quickly use my cheap handheld gps to know exactly my distance and direction from that hazard. It may not be a chartplotter, but it gives the info I need...especially when the chart plotter goes down.

There are many other nav techniques they could have used...but did not.

I would have been more sympathetic if their engine had failed, rather than the chartplotter.
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Old 14-01-2016, 10:01   #27
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Re: What happens when your navigation systems fails

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Originally Posted by S/V Alchemy View Post
Simple. I have a sounder, a paper chart, and a bearing compass. If the sounder's gone, I have a leadline. I also have the current almanac, an accurate timepiece and a few sextants. None of which are convenient, but all of which can get me home.
+1.

I don't have the sextants, but I'm not crossing an ocean...most of the time. When I did cross the atlantic, my decades old garmin etrex (walmart $99) was all I used. The owner/skipper had $10,000 in new electronics, and a sextant...not needed.

In mid ocean, you can make your own cheap chartplotter...draw a triangle on a blue piece of paper...there you go, done!
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Old 14-01-2016, 10:20   #28
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Re: What happens when your navigation systems fails

i think these sailors were on a delivery mission. In the last minutes of the nuclear treaty discussions, The Iranians threw out, "oh and we'd love to have a couple of those riverine command boats."

"We can't give or sell you arms." Says Kerry

"Just deliver a few inside our boarder and we'll take it from there and give your crews back."

Just me speculating
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Old 14-01-2016, 10:28   #29
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Re: What happens when your navigation systems fails

Back in the 1980s a blind guy sailed successfully across the Atlantic; another guy sailed around the world without any navigation aids, none. Since the world is reasonably round, you really can not get lost. Sail long enough and you will hit a continent. So at the macro level, navigation is duck soup. At the micro level of navigating a channel or picking your way through a reef system, then your fairly screwed without navigational aids of some sort.
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Old 14-01-2016, 10:30   #30
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Re: What happens when your navigation systems fails

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Originally Posted by blewett_john View Post
You use a paper chart, plotting paper, and a sextant.

I read some years ago that the USN eliminated celestial navigation from their Officers training.
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