So its not just our imagination, and can be dangerous!
www.news.com.au/technology/innovation/military/gps-signals-jammed-norway-finland-warn-pilots-russia-may-blind-their-navigation-systems/news-story/ee28be793012e9b9e66d59ffba439242
Here's a story from back in the day.
We'd pulled out of the '90 (???) Hobart and were doing the predecessor to the Geelong regatta. I was navigating and as we weren't locals I was spending a fair bit of time downstairs on our newfangled GPS unit, trying to find marks and things. The unit used to give an estimated circle of accuracy for the fix and one day I noticed it had gone from huge metres down to about a metre. I mentioned it to the guys about how the accuracy was super good but I didn't know why. We went home that night to see the air war for Desert Storm had just started. Seems there weren't enough of the military decoders around so they turned down the error for a while... 
GPS is handy but I believe it still does not stand in a court of law.
There is nothing really hard to do when coastal navigating with a bearing compass, sounder, log, parallel rule, dividers and paper charts.
People these days are more mentally lazy than they are physically lazy.
Yes I think you are right Cisco. There is no tracability regarding the relation between a gps point and a given chart.
And similar to what Jethrow mentioned we often have 5 or 10 Treks lined up on our window sill and I ping them from home. Some months ago a group of 5 stubbornly moved their location 30m west. Next morning back to normal. I wondered if the yanks were trying to make one of Kim's missiles do a u turn 
Well, Trek, you might remember the posts on the vulnerability of the GPS system to terrorist interference. I was hooted down by the non-believers in Russian and Chinese evil and general belligerence.
Because they are evil and belligerent, no doubt!
Well, here we go again, and we are still not arming ourselves - mentally, morally, economically as well as physically - against those two potential terroristic states Russia and China - and their interference.
The US is the third side of the triangle but at least it is on our side, we hope.
No, we cower, we appease and assuage to their demands and to our "economic interests" which is the rope on which we are going to be hanging sooner or later. By that time free GPS will be just a story from the past.
Australians who had no first hand experience with communist states and their politics and philosophy - Marx, Engels, Lenin, Mao - have no idea of their deep seated hatred of their opposites and twisted ideology. Their philosophy has logical continuation in the new governments and political leadership of those two countries, openly communist or otherwise and their satellites.
They are the same wolfs in different fleece.
The clandestine, malignant interference with - beside the GPS or GLONASS systems - anything and everything in their interest is not just possible, it is a given. They are dwelling on it ever since they existed.
Just think of the USSR's huge operation to interfere with Radio Free Europe and Voice Of America. They don't give a hoot about international treaties, politics, law at all, less their interest requires so.
Reagan was right when he called the USSR "the evil empire" 
. Why would it be different with the GPS system?
The interference with the GPS system is not just likely in case of hostilities, but it is a necessity. If one is foolish enough to deny this, one does so at his own peril.
Cherish the old maps, charts and brush up on your navigational skills, asap.
Select to expand quotecisco said..
GPS is handy but I believe it still does not stand in a court of law.
There is nothing really hard to do when coastal navigating with a bearing compass, sounder, log, parallel rule, dividers and paper charts.
People these days are more mentally lazy than they are physically lazy.
Let's see , chart says I need to steer 5 degrees true . Now compass rose says variation 11 degrees east .
From class " variation east compass least" .
So ,I deduct 11 from 5 that gives minus 6? or does it give 354 ?
But 354 is greater than 6 not least.
Bugger where's the gps.
Yeah, it ain't funny thou, when the satellites are blown up and 300 feet below your keel! 
^^^ Didn't yo just purchase a GPS
Charts are only as accurate as your pencil is sharp, your ruler is straight and your eyesight is good. It is not hard to be a mile or two out whilst the whole process is subject to human error.
My livelihood (as a few others in here) and my life depends on the accuracy of the GPS network. As far as I am aware, we do not use the American network anymore and Selective Availability was turned off back in the Clinton days. I will trust the system, but I am also well aware of its flaws.
Trek, I am sure you are aware on how weak a GPS signal actually is. I am not surprised you occasionaly get errors with your Trek system even sitting on a window sill. Out of curiosity, I set an anchor alarm on my iPad and sat it on my bed for a few hours. The drag alarm went off in matter of minutes. A few hours later, the drag track was in the neighbours yard (I don't live on a small suburban block either).
An iPad GPS won't be of the same caliber of an A-380's doing a full autoland, but Im not running to the hills just yet.
Yeah, Toph, aren't you aware of the fact, "hope dies last!"?
I am not worried of the system as such,
I am worried for it!
Even the Navy now relies on GPS and chart plotters. A visit to an Armidale Class Patrol Boat will show you how it is done now. I doubt the Navy would rely on something that isn't legal.
The satellite navigation system in the early 90s being used by yachts probably was not GPS but rather transit nav. Transit nav relied on the proximity of the satellites to the platform so positions could be far in error or very close. It was transit nav back then that gave error probability circles.
Although GPS was allowed for civilian use in the 80s it wasn't fully operational until 1995 and didn't come into common civilian use until the mid 90s.
There are far more opportunities for navigation errors using manual nav than there are using GPS and chart plotters. I can attest to both being a professional navigator in my past using both systems. My big stuff ups were due to errors in plotting, avoided now with chart plotters and GPS.
"The Navy and other branches of the U.S. military are becoming increasingly concerned, in part, that they may be overly reliant on GPS. "
www.npr.org/2016/02/22/467210492/u-s-navy-brings-back-navigation-by-the-stars-for-officers
But the possibility of failure of the GPS system is all that is keeping some of the old buggers going! They're just dying to be able to say, "I told you so" as they wave their brass dividers for the last time!
Chuckles intended.
Bristol
Select to expand quoteBristolfashion said..
But the possibility of failure of the GPS system is all that is keeping some of the old buggers going! They're just dying to be able to say, "I told you so" as they wave their brass dividers for the last time!
Chuckles intended.
Bristol
Yep.
There are probably better ways of combating the reliance on GPS as a single point of failure than training in astro nav. If you have to rely on astro nav, which I did, you have big problems. Incorporating secret codes into the GPS would be smarter, the yanks do control it.
There is a book called Ghost Fleet.
www.abc.net.au/radionational/programs/latenightlive/peter-w-singer-ghost-fleet/6726332
It envisions a clash between China and the US that, shell we say, gets out of hand.
The first thing to go are the satellites.
Knocking out communications and tracking systems would logically seem the first choice in any major conflict.
Unfortunately, the debris from this sort of scenario makes the most useful orbits, useless.
Back to cables for communications and sextant for navigation.
That is if there is a back to.
A great read.
gary
Well back in the day before GPS it was common to find coastlines up to a mile out, especially when you could note that the chart was based on one done by such as Cook and Bass!
That all disappeared with GPS so our charts today are more accurate, gotta have them on board to be any use though!!
In the last few outings offshore I've noticed twice a fairly significant degradation of both GPS' to the point of losing synch. Worst case was for maybe 45 mins., other was no more than 10-15 mins.
A check of the GPS showed both times there were enough satellites visible, but all were low enough on the horizon to cause a loss of synch.
Select to expand quoteMorningBird said..
Yep.
There are probably better ways of combating the reliance on GPS as a single point of failure than training in astro nav. If you have to rely on astro nav, which I did, you have big problems. Incorporating secret codes into the GPS would be smarter, the yanks do control it.
There are built in time correction factors that can be manipulated to show any result that they want you to see, so in essence they are like a code. This is why military GPS systems are many more time accurate than civilian ones.
President Clinton turned GPS Selective Availability off but you need to bear in mind that it can be turned back on just as easily.
At the moment you have GPS (USA) and GLONASS (Russian), the Chinese BeiDou system and the EU's Galileo systems expected to be deployed by 2020, followed some time later by Indian, French and Japanese systems. All you need do now is buy receiver to cover each of those systems and you should always know where you are
Select to expand quoteBananabender said..
Let's see , chart says I need to steer 5 degrees true . Now compass rose says variation 11 degrees east .
I abide by the rule that True Virgins Make Dull Company ie, True + or - Variation = Magnetic + or - Deviation = Compass.
Simple stuff!!
When coastal navigating I like doing my three bearing and running fixes etc to compare the GPS against to determine how inaccurate the GPS is day to day.
Select to expand quotenswsailor said..
Well back in the day before GPS it was common to find coastlines up to a mile out, especially when you could note that the chart was based on one done by such as Cook and Bass!
That all disappeared with GPS so our charts today are more accurate, gotta have them on board to be any use though!!
There are still large errors in charts. Check the dates on your new charts. Some in NSW are still based on Cooks charts.
I love my I pad while sailing we just delivered a boat up from Sydney last weekend never more than 250 meters offshore as the current was ripping I pad in cockpit at all times lots of ticking off on the chart as well I always remember shockwave being written off on the rocks people dying because the yanks had disabled the gps while they were killing arabs this was the stated reason at the inquiry
conclusion gps awesome don't rely on it
Select to expand quoteboty said..
" because the yanks had disabled the gps while they were killing arabs this was the stated reason at the inquiry "
"The inquiry could not identify a single reason or cause of the accident but we have identified a series of errors in judgement, which by themselves could have been inconsequential, but combined are contributory factors to the tragic grounding,"
www.abc.net.au/news/2010-02-25/fatal-yacht-crash-inquiry-blames-gps/343272
Select to expand quotecisco said..Bananabender said..
Let's see , chart says I need to steer 5 degrees true . Now compass rose says variation 11 degrees east .
I abide by the rule that True Virgins Make Dull Company ie, True + or - Variation = Magnetic + or - Deviation = Compass.
Simple stuff!!
When coastal navigating I like doing my three bearing and running fixes etc to compare the GPS against to determine how inaccurate the GPS is day to day.
You reckon a running fix will be more accurate than GPS? Errors in taking bearings, chart errors, plotting errors and in estimating speed oover the ground add up to big errors. You are really checking how inaccurate your fixing is compared to GPS.
It is frustrating to read a report that seems to point to different conclusions.
The following passage would indicate that the navigator and deck crew share the blame for the accident.
"What is difficult to understand is why a visual reference was not made to the islet..." the report said."[The crew] could see the whole islet including the low ledge to the north when one mile away."The inquiry cannot understand why the course was not adjusted to pass clear to the north and why with 18 people on board, somebody did not draw attention to the fact the boat was heading straight for the rocks."
Then this passage would indicate that the GPS device inaccuracy was a primary cause.
The inquiry found the main reason for the crash was that the crew relied too heavily on an inaccurate GPS chart plotter that was out by at least 100 metres.
Wouldn't a professional navigator be aware that GPS has inaccuracies and make allowances for that?
A lesson for me.
Anyway, I wasn't there, so I will leave it to the experts
gary
When l came down the NSW coast l could tell where we were by looking out the window!
Select to expand quotegarymalmgren said..
It is frustrating to read a report that seems to point to different conclusions.
The following passage would indicate that the navigator and deck crew share the blame for the accident.
"What is difficult to understand is why a visual reference was not made to the islet..." the report said."[The crew] could see the whole islet including the low ledge to the north when one mile away."The inquiry cannot understand why the course was not adjusted to pass clear to the north and why with 18 people on board, somebody did not draw attention to the fact the boat was heading straight for the rocks."
Then this passage would indicate that the GPS device inaccuracy was a primary cause.
The inquiry found the main reason for the crash was that the crew relied too heavily on an inaccurate GPS chart plotter that was out by at least 100 metres.
Wouldn't a professional navigator be aware that GPS has inaccuracies and make allowances for that?
A lesson for me.
Anyway, I wasn't there, so I will leave it to the experts
gary
Gary,
It's a good point though, we all need to regularly check to make sure we not getting complacent. I try and offset the risk by little changes in things I do, like building in some fudge on the course gps co-ordinates given for a race. A lot of times the turning marks will be official navigation marks, so I'll plot a course using their given gps co-oridnates, then I'll go through each one and move each waypoints position toward safe water by 100mtr or so than the actual mark of the course. This is what is provided to the helm as the course to steer, which means we over-stand the real waypoints by a bit.
Not the most efficient way to race admittedly, just mitigating the impact of any drift or inaccuracies in GPS.
Another cheat, especially racing at night, I use as the default display on the GPS the satellite signal screen option. This is the one that shows you the available satellites and the strength and quality of the signal from each one. It sits in my peripheral vision when I'm sitting at the chart table, and because its graphical its quick and easy to read. Checking other info or display templates is only the press of a button away,
Select to expand quoteMorningBird said..cisco said..Bananabender said..
Let's see , chart says I need to steer 5 degrees true . Now compass rose says variation 11 degrees east .
I abide by the rule that True Virgins Make Dull Company ie, True + or - Variation = Magnetic + or - Deviation = Compass.
Simple stuff!!
When coastal navigating I like doing my three bearing and running fixes etc to compare the GPS against to determine how inaccurate the GPS is day to day.
You reckon a running fix will be more accurate than GPS? Errors in taking bearings, chart errors, plotting errors and in estimating speed oover the ground add up to big errors. You are really checking how inaccurate your fixing is compared to GPS.
I have not had the pleasure of using gps in ocean or coastal traversing of a night but I would imagine even the helmsman would be able to see
on screen the boats position and course and make adjustments where necessary.
Thats a hell of a lot different to be given a course to steer by compass and have total faith in the navigator.
Coming home from a race with the ORCV short handed in the olden days I plotted a course and gave it to watch leader while I went below at 2200 hrs. Four hrs on Four off.
Thank God the weather lived up to the name of the headland we were steering straight toward ,"moonlight head" and I was jolted awake by
the boat gybing before we hit the rocks.
To this day I can't work out what mistake I made and can only guess there were currents I was unaware of.
Even now in my limited sailing I refer to laminated maps when in unknown waters but if dark it would be GPS all the way.
To be clear, for many years I derided GPS and relied on traditional nav but learnt my lesson a few times.
I now use GPS as the primary but I keep a chart plot as well and even take bearings, just for fun.
GPS error?
www.sail-world.com/news/212237/Route-du-Rhum-leader-runs-agroundhttps://www.routedurhum.com/en/news/1041
Mouse is right - when I'm on watch & I know where I am by, well, watching!
Not much use out of sight of land, of course.
Cheers
Bristol
