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Old 30-07-2013, 22:09   #16
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Re: Dust Off Your Sextants! GPS Hacked!

The moral of the story appears to be "don't allow anyone with suspicious looking blue briefcases on your superyacht".
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Old 31-07-2013, 00:01   #17
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An autopilot can steer to a compass direction manually entered in the AP's control unit

You can even manually alter the compass course to steer a different direction from the compass direction you entered.

You can even turn the AP off and manually steer to the course indicated on the gps.

You can even turn both the gps and the AP units off and steer to the wind.

You can certainly do those things. However, if you refer to the quote in my post, you can see that I was asking in reply to a poster talking about disengaging the auto pilot from outside sources of information. A compass based one would be even easier to mess with, use a magnet!

The other forms of steering you mention are exactly what I think you'd have to use if you decided to run your autopilot without external sources of information.
Nothing wrong with those, but then I don't think it qualifies as using the autopilot at all
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Old 31-07-2013, 02:06   #18
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Re: Dust Off Your Sextants! GPS Hacked!

This research was obviously funded by paper chart makers.
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Old 31-07-2013, 02:46   #19
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Re: Dust Off Your Sextants! GPS Hacked!

Quote:
Originally Posted by Adodero View Post
......
On a similar note, do marine GPS units not provide RAIM?
No

Quote:
Originally Posted by John A View Post
What's RAIM??
Receiver Autonomous Integrity Monitoring.

You can google it for full details but in essence, it is a process were the GPS checks itself by using several different combinations of the available satellites to plot it's position.

If there is a big difference in these positions, it assumes something is wrong - usually dud satellite data. It has to have enough satellites in view to do the checks so RAIM can be lost if there aren't enough visible satellites at any given moment.

Note this is only a quick and dirty explanation and not 100% accurate in detail
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Old 31-07-2013, 08:56   #20
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Re: Dust Off Your Sextants! GPS Hacked!

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Originally Posted by Wotname View Post
No


Receiver Autonomous Integrity Monitoring.

You can google it for full details but in essence, it is a process were the GPS checks itself by using several different combinations of the available satellites to plot it's position.

If there is a big difference in these positions, it assumes something is wrong - usually dud satellite data. It has to have enough satellites in view to do the checks so RAIM can be lost if there aren't enough visible satellites at any given moment.

Note this is only a quick and dirty explanation and not 100% accurate in detail
Thanks.

And if you monitor the display of satellites in use you'll see that your gps unit is constantly loosing and acquiring satellites. You can completely lose gps reception in heavy seas, for brief periods..
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Old 31-07-2013, 09:01   #21
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Re: Dust Off Your Sextants! GPS Hacked!

One more reason to not hook your self steering to your GPS....
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Old 31-07-2013, 09:35   #22
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Re: Dust Off Your Sextants! GPS Hacked!

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another vote for not tying your Ap to anything else.....
Indeed. My sextants have never actually collected dust, and when I went to a new (to me) harbour last weekend, my wife bought us the paper chart.

I used the paper chart to determine bearings (I use a handheld pelorus), to familiarize myself with the anchorage areas, should that have become desirable or necessary, and to check chart datum depths. My sounder confirmed that we currently have lake levels up a fair bit. I used the GPS to figure out ETAs and offsets from waypoints like known buoys. As it was a bright, clear day and I could identify landmarks easily, I did not bother with the sextant. Fogged in shore, at night, or on a barren stretch, I do occasionally use it.

GPS is great...a huge help. But I do not consider it definitive or the only method of locating oneself. Aside from the obvious need GPS receivers have for batteries or ship's power, there have been irregularities over the years, such as "5 knots....5.1 kn....67.2 kn....4.9 kn...." as one of the four or five satellites acquired has a reset or a thruster burp or is nudged by a coronal discharge. GPS doesn't often go wrong, but a subtle error could in fact go unnoticed unless the skipper is using at the same time other methods of pilotage.

APs are best set on bearings provided by fluxgate compasses, or even from chart-acquired paperwork. Deviations from course are revealed pretty quickly and valuable inputs about making lee, drift and current set are seen. The idea of GPS being hacked in order to skew a ship's AP to either drive it ashore or toward pirates (as an example) is a nightmare prospect akin to hacking a pacemaker and gradually increasing someone's heart rate.

Use GPS as only one input of many, however, and a "hacked" GPS is revealed before trouble can take root.
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Old 31-07-2013, 11:26   #23
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Re: Dust Off Your Sextants! GPS Hacked!

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Originally Posted by John A View Post
Thanks.

And if you monitor the display of satellites in use you'll see that your gps unit is constantly loosing and acquiring satellites. You can completely lose gps reception in heavy seas, for brief periods..
There are other conditions that can cause it to be lost, too. It's not uncommon for GPS units to either lose satellites, not acquire enough to be accurate, or get invalid data for various reasons.

Most RAIM enabled GPS units I've used alert you when RAIM is 'lost', which is a part of regulatory requirements for those uses. I find it somewhat disturbing that marine GPS units don't provide RAIM or even some more rudimentary forms of integrity monitoring. If acquisition of a certain # of satellites fails, you could be way off course, with the GPS showing an inaccurate position and no clear indication of the failure.
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Old 31-07-2013, 11:35   #24
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Re: Dust Off Your Sextants! GPS Hacked!

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Originally Posted by S/V Alchemy View Post
Indeed. My sextants have never actually collected dust, and when I went to a new (to me) harbour last weekend, my wife bought us the paper chart.

I used the paper chart to determine bearings (I use a handheld pelorus), to familiarize myself with the anchorage areas, should that have become desirable or necessary, and to check chart datum depths. My sounder confirmed that we currently have lake levels up a fair bit. I used the GPS to figure out ETAs and offsets from waypoints like known buoys. As it was a bright, clear day and I could identify landmarks easily, I did not bother with the sextant. Fogged in shore, at night, or on a barren stretch, I do occasionally use it.

GPS is great...a huge help. But I do not consider it definitive or the only method of locating oneself. Aside from the obvious need GPS receivers have for batteries or ship's power, there have been irregularities over the years, such as "5 knots....5.1 kn....67.2 kn....4.9 kn...." as one of the four or five satellites acquired has a reset or a thruster burp or is nudged by a coronal discharge. GPS doesn't often go wrong, but a subtle error could in fact go unnoticed unless the skipper is using at the same time other methods of pilotage.

APs are best set on bearings provided by fluxgate compasses, or even from chart-acquired paperwork. Deviations from course are revealed pretty quickly and valuable inputs about making lee, drift and current set are seen. The idea of GPS being hacked in order to skew a ship's AP to either drive it ashore or toward pirates (as an example) is a nightmare prospect akin to hacking a pacemaker and gradually increasing someone's heart rate.

Use GPS as only one input of many, however, and a "hacked" GPS is revealed before trouble can take root.

You use a sextant in fog???? Must have pretty wimpy fog where you are.

I think it's kind of funny that people actually think that a system that is completely disabled, often for days, by something as simple as a cloud and is accurate to a mile or two if you are really really good at using it is, superior to an all weather system that is accurate to a few feet, just because it may occasionally glitch for a few seconds. I suspect that the 67 knot reading was caused by a software issue in your unit or passage under a bridge that blocked the signals for a few seconds, not by the GPS system. Of course I would guess you are updating your position and calculating your speed over the ground once every second with your sextant of course. I'm sure that no one that uses a sextant ever makes a calculation error, after all people are definitely superior to machines when doing calculations at high speed.

Next you guys will be insisting that a lodestone floating on a piece of wood is superior to a modern compensated compass.
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Old 31-07-2013, 12:18   #25
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Re: Dust Off Your Sextants! GPS Hacked!

Old news, another group did it to a drone earlier this year. This is just "me too!"

And something like 15 years ago, ALT2600 discussed GPS spoofing and brought up these issues. Yes, any idiot can spoof a GPS, the problem is that your fake signal only has to be stronger than the satellite signal.

Which co-incidentally means your spoofing signal will be the strongest signal around.

Which also makes your signal the highly visible target for the "antiradiation" missile that someone is going to fire, to take out the spoofing source if it runs for any length of time. Yes, even fifteen years ago. No one is going to openly discuss it, but the technology and equipment exists. One spoofer might get away with it. Maybe even two or three. But then...the need for pension plans in the spoofing business won't be around much longer.

Meanwhile, it is equally convenient for certain parties to be able to spoof.
All old news.
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Old 31-07-2013, 12:19   #26
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Re: Dust Off Your Sextants! GPS Hacked!

It does not matter whether the AP is tied to the system or not. It is the fix from the GPS that is faked. So even if you are using paper charts, you will still be getting bad fixes off your GPS. The civilian GPS can be disturbed by the military or from overpowered local broadcasts. Pretty unlikely, unless you are in a war zone.
AIS is pretty easy to disrupt too. Night before last I had an AIS target displaying >655 miles away with a description something like: a navigation buoy that was not physically in place, with an MMSI number of 1234567890.
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Old 31-07-2013, 12:56   #27
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Re: Dust Off Your Sextants! GPS Hacked!

You use a sextant in fog???? Must have pretty wimpy fog where you are.

I use a sextant when the shore is obscured by fog, but I can use an artificial horizon and get a clear sun shot, sure.

I think it's kind of funny that people actually think that a system that is completely disabled, often for days, by something as simple as a cloud and is accurate to a mile or two if you are really really good at using it is, superior to an all weather system that is accurate to a few feet, just because it may occasionally glitch for a few seconds.

I didn't say it was superior. I did imply that it had attributes that made CN both an alternative and an adjunct to GPS-based navigation. I am in fact arguing for ALL "systems" of navigation as maintaining relevance...as opposed to one, which may be reduced to none.


I suspect that the 67 knot reading was caused by a software issue in your unit or passage under a bridge that blocked the signals for a few seconds, not by the GPS system.

Open water every time. It's happened with two different units over seven or eight years. GPS is not perfect and can be jammed, hacked, switched off, made less accurate or even screwed up by sunspots or CMEs. Most of the time, it's fine, but how is one to notice when it isn't fine if one is utterly reliant upon only GPS? Are you looking forward to the self-driving car, too?

Of course I would guess you are updating your position and calculating your speed over the ground once every second with your sextant of course. I'm sure that no one that uses a sextant ever makes a calculation error, after all people are definitely superior to machines when doing calculations at high speed.

Practice helps. Errors happen, but are usually gross and therefore obvious. The sun and the stars, while occasionally obscured, can't easily be "turned off". That's why CN, despite its clear shortcomings, remains viable. Beats Sudoku for me, anyway.

Next you guys will be insisting that a lodestone floating on a piece of wood is superior to a modern compensated compass.

I guarantee my Ritchie Globemaster is a very good compass. I'm arguing that the superior solution is not to rely exclusively on GPS, but to embrace many forms of nav aid input: GPS, CN, pilotage, paper charts, bearings, compass, depth contours...hell, chuck a lead line if you have the chart, your batteries are dead and you believe you are in soundings. The point is to exhibit seamanship. Relying on single means of discerning one's position is not, to me, good seamanship. If it's different on your boat, fair enough. Navigation isn't an article of faith, after all.
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Old 31-07-2013, 12:58   #28
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Re: Dust Off Your Sextants! GPS Hacked!

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It does not matter whether the AP is tied to the system or not. It is the fix from the GPS that is faked. So even if you are using paper charts, you will still be getting bad fixes off your GPS. The civilian GPS can be disturbed by the military or from overpowered local broadcasts. Pretty unlikely, unless you are in a war zone.
AIS is pretty easy to disrupt too. Night before last I had an AIS target displaying >655 miles away with a description something like: a navigation buoy that was not physically in place, with an MMSI number of 1234567890.
Agreed, it's pretty unlikely, but in a throughly convenient world, unlikely things happen more often than they used to. I find a touch of skepticism at the helm is the most profitable course when the gadgets seem to be reporting unlikeliness.
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Old 31-07-2013, 13:13   #29
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Re: Dust Off Your Sextants! GPS Hacked!

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Agreed, it's pretty unlikely, but in a throughly convenient world, unlikely things happen more often than they used to. I find a touch of skepticism at the helm is the most profitable course when the gadgets seem to be reporting unlikeliness.
I think read somewhere on one of my old, musty paper charts: The prudent mariner shall not rely solely on any single aid to navigation....
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Old 31-07-2013, 13:26   #30
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Re: Dust Off Your Sextants! GPS Hacked!

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I'm arguing that the superior solution is not to rely exclusively on GPS, but to embrace many forms of nav aid input: GPS, CN, pilotage, paper charts, bearings, compass, depth contours...hell, chuck a lead line if you have the chart, your batteries are dead and you believe you are in soundings. The point is to exhibit seamanship..[/B][/I]
And that statement boys and girls is what pilotage is all about. The rest is details.
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