GPS anxiety

lustyd

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Just to split hairs ....
Split away! Ultimately the details don’t change the fact that people in boats have been safely getting back to land for probably thousands of years without GPS or charts. There comes a point where navigation must be replaced with seamanship and pilotage regardless of the system in use.
The chance of GNSS systems all being down is low enough that it’s not a sensible thing to spend time on for the average sailor.
 

ShinyShoe

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All of the time sources on my boat apart from the decorative brass clock use live GPS time so corrections are irrelevant. RTCs don’t suffer noticeable drift these days anyway even if they did disconnect for a few minutes.
I guess if my hobby was taking sights I’d also have an old chronometer on board to add to the fun.
Do you not have a phone?
My phone, tablet, laptop, etc all have clocks that are adjusted from some source (phone - network) others internet NTP server. All likely set from something like GPS. BUT - none of which will stop working when I'm a steal box.
But let’s not forget that Columbus managed to find the Americas not only without a chart but before longitude could be measured.
Was my history wrong >> was he not looking for Indja 😂
 

Sandy

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It’s just what the chips are called. 3 axis (x,y and z) for compass, accelerometer and rotation making 9 readings in total which can be used together for all sorts of cleverness. On boats they will show pitching, wave height, heel etc. on a watch it can tell me what stroke I’m doing while swimming or how much bounce I have when running. It can even measure pace when running just with wrist movements.
Thanks. In engineer speak 'marketing hype' then.
 

lustyd

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Thanks. In engineer speak 'marketing hype' then.
Not at all, just a bad choice of words. There’s no hype there are 9 readings in three categories all of which add up to a gimballed compass replacement. Without the additional 6 readings you can’t make a working compass hence the term 9axis compass. The additional information is very useful though and has led to significant enhancements to autopilots as an example.
I suspect it wasn’t marketing hyping something it was engineers who couldn’t be arsed to explain to laymen what was actually going on so they just said “better compass”.
 

Refueler

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Not at all, just a bad choice of words. There’s no hype there are 9 readings in three categories all of which add up to a gimballed compass replacement. Without the additional 6 readings you can’t make a working compass hence the term 9axis compass. The additional information is very useful though and has led to significant enhancements to autopilots as an example.
I suspect it wasn’t marketing hyping something it was engineers who couldn’t be arsed to explain to laymen what was actually going on so they just said “better compass”.

The use of axis actually is done with as little as 6 to have full data of direction, rate of turn, pitch and roll ...

Its actually the first time I have heard of 9 ..... and that's after years of drone use - where 6 are the norm for accuracy of autonomous flight ... return home / data display on screen etc. etc.
 

lustyd

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Drones won’t need the accelerometer to measure movement as they have gps and altimeter data usually. The chip will be 9 axis though I’d imagine, they’re cheap and ubiquitous. The drone would probably use the gyro sensors to complement the magnetic data and to keep the craft upright.
 

Buck Turgidson

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For those wondering what the 9 axis are. Its x,y,z linear x,y,z angular and x,y,z, magnetic.
6 axis gives all the accelerations needed to measure movement. The last three allow that movement to be used with reference to locally sensed magnetic north.
 

MontyMariner

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I am truly amazed as to why people are so exercised by the problems that a loss of gps would have on their ability to navigate at sea, especially when most of the trips are coastal with a few x Channel's PA thrown in. The global consequences would be/ should be of much more concern, like I won't be able to phone home from the car to say to the minute what time I'll be home and to have dinner ready! 😭
 

AntarcticPilot

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Just to split hairs ....

Columbus did not actually find America ... he landed on an island - which one is still in dispute ! But its plain that he did not reach the mainland.

Longitude was not really an issue as long as navigator played the game of not aiming for the destination - but upwind of it ... He relied on the Latitude far more ...
In old days - of course they used Lunar tables to try and get round the Longitude mess ... glad that got binned !!
Just to clarify! Columbus had no means of determining longitude except dead reckoning. Both the method of lunars and the chronometer were 18th-century inventions, resulting from the offering of a vast money prize by the British government. As @Refueler implies, the method of lunar distances was challenging for the average mariner, and was never in widespread use; chronometric longitude was much simpler and more accurate. Cook used the newly invented Lunar method only on his first voyage with considerable success, but he had several advantages - not least having a professional astronomer on board! The observation of the transit of Venus in Tahiti also gave him a very good known longitude. But on his second and third voyages he developed techniques to use lunars and chronometers together and achieved accuracies that were good enough to remain in use until the 20th century. It is noteworthy, and a lesson perhaps for all of those who rely on a single method of navigation, that Cook used ALL the techniques at his command to achieve results much better than any single technique could achieve.

To give a flavour, on his third voyage, Cook was aware of deficiencies in the lunar tables he used - there was a periodic error that resulted from the ephemeris of the Monn not being as well characterized as it is now, and of course, all computation was manual. But equally, his chronometers were of varying quality and reliability (only one lasted the whole voyage). By using the two together, he was able to reduce the error in his positions to less than a nautical mile - an amazing accuracy for the period, especially when you consider that many navigators were uncertain of their longitude by several degrees!
 

Refueler

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Drones won’t need the accelerometer to measure movement as they have gps and altimeter data usually. The chip will be 9 axis though I’d imagine, they’re cheap and ubiquitous. The drone would probably use the gyro sensors to complement the magnetic data and to keep the craft upright.

Sorry but 101% wrong ......

Drones DO use accelerometers - we are not talking the 10 quid supermarket indoor toys ...

The accelerometers are used for various incl RATE of turn in all axis ... they are the 3D element of the Drones arsenal .....

Drones GPS is actually on par or better than you have on your boat ... but Altimeter is usually based on Barometric change from that of take off point. GPS altitude is crap at best of times even with latest multi sats ...
The accelerometer detects the rise and fall far faster than any barometer / GPS ....

The level or flight attitude is maintained by the Gyro sensors - agreed - but the RATE of change etc. is by accelerometers ...
 

lustyd

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The accelerometers are used for various incl RATE of turn in all axis ... they are the 3D element of the Drones arsenal
Literally what I said. They use the gyros. They don’t need the linear accelerometers because they can measure movement in 3 dimensions so don’t need to sense that part of the equation.
 

Daydream believer

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My first 10 years of sailing relied on guess work & a Sestral grid compas (which still gets me lost to this day) & an echo sounder. I rely heavily on both. More so the echo sounder, if I can see some known marks such as wind farms etc. Then I can cut the corners of sand banks.
As a result I often donot bother to turn the GPS on, if it is light winds & I am motoring along the coast, or across the Thames estuary, to somewhere like Ramsgate. There are so many markers these days, it is easy.
However, further offshore & the short leg just before North Foreland, I like the AIS & my Yeoman, so have everything on. I write my position on a pad every hour, or when I reach a point of note, for later entry in the log.
 

st599

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But with most people carrying lots of mobile devices with GPS, and most of us have charts on some of them also, ships power failure should not result in loss of a GPS position (if it does you have failed to prepare). The real issue is if the GNSS signals are blocked or stopped by an external event.
Being blocked is not the main issue, GPS (and Galileo, Beidou, Glonass etc.) are so low power, they are really easy to spoof.

Ask England fans in Moscow trying to find the world cup venue. Their phones were apparently doing an impression of Concorde, Mach 2 at angels 11 in random directions.

The issue isn't loss of signal, but a believable spoof signal.
 

lustyd

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All of the modern GNSS systems support encryption so if spoofing were to become an issue it would very quickly be enabled for civilian use. It isn’t a real world issue today though
 
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