Tuesday, Sep 01, 2009 at 18:05
[quote]not some hoodoo about how, if you’re out in the scrub with a GPS and it happens to stop working, youre in big trouble e.g. Just get out the spare GPS you bought along for just this occasion - what’s wrong with that solution?[/quote]
Whats wrong with that solution?
God forbid should I ever be unfortunate enough to go anywhere off the beaten track with you - that I have the smarts not to go in the first place.
I can tell you from experience, why your backup plan is one day doomed to fail.
Yet I too carry spare GPS - in case one goes on the fritz. But I also carry the paper chart and compass. You have no business being out there without them.
Do you have the requisite intelligence to learn from the answer to your own question or am I waisting my time explaining it too you?.
This is a lesson I learned from experience about this fancy new technology.
It doesn't always work.
You contend no need for backup chart and compass & that the manufacturers statement about NOT using it for primary navigation is merely a statement against liability.
Facts are - no it isn't, its advice meant to save your life from navigational mistakes in the GPS system.
They are rare, but they do occur - I can recall 3 of them so far in my experience so far.
In order to be a professional skipper licensed to take plebs like you out to sea and return, as a paying fare I had to pass navigation.
One of the things they teach you - is why that statement on the equipment isn't just some manufacturers liability statement and why it is put there to stop people exactly like yourself from making serious mistakes of judgment.
GPS relies on several things, including your handset or receiver.
If one goes on the fritz sure grab another spare, but what about when it isn;t the hand set that's faulty?
What about when you can't get a signal?
Say under temperate rain forest canopy with more than 90% canopy cover?..what good is that spare GPS then?
A compass will still work tho - and a map n compass might save your sorry butt!
What if your in a
cave - same thing, map of the
cave and a compass and a flashlight and hard hat and caving gear and your good to go - or in your case stand there with two perfectly useless GPS handsets and hope someone with more knowledge that you comes saves your sorry hairy butt!
What if, one of the NASA technicians, who looks after satellites has to "re boot" the computer aboard a satellite, after updating its software?
What if when he does he makes a human error and - forgets to re set the clock - or sets it to his local time rather than UTC time etc.
People are human people make mistakes it has happened before today!
It's called a simple clock time error.
What effect does it have?
Well on a satellite, the satellite has to know were it is in space in relation to points on earth but ALSO, WHEN it is, in space, in order to know WHERE.
With a simple clock time error a satellite incorrectly reports its position in space - and that incorrect data when it is calculated by your handset, can triangulate your position, depending on the number of satellites in view at any given time, anything up to 200 nautical
miles out - as happened to Australian aviation some years back - where commercial passenger jets were displaying their position as 200 Nmiles off the east coast over the pacific ocean - while the pilots could clearly see the coast as they made their approaches to
Sydney Airport.
Why weren't they off track and out over the ocean due to the clock time error on a satellite?
Because like me, - as a qualified navigator - they file a flight plan and plot it manually on the charts and maintain a check with bearings and compass etc as their PRIMARY source of navigation - while their GPS is only a backup to confirm what they already know.
Thats why they don't let YOU fly those jumbo's, its safer for all concerned if someone who actually knows how to navigate is at the controls.
Using your logic any idiot with 2 GPS can navigate a plane!
When else doesn't the GPS system work.
1. When the mainland USA is under attack (9/11).
2. When the USA is going to War against another nation (Gulf War 1).
It so happens I was studying navigation as part of my skippers course in 2001, and it started in late August and went thru too about the 3rd week in Sept.
I happened to have bought a Garmin etrex summit waterproof mountaineering GPS, with altimeter, barometer and the works in it.
It was neat - I could check my manual paper chart
routes, against GPS route data, to confirm I'd got it right with my position plots bearings etc and I had a backup.
No one else at the course had one including the instructor, we all got to have a play with it.
I knew from past experience with a GPS during Gulf War 1 and ol Stormin' Normin Swartzkopf, that the Yanks play with their satellite data when they are going to war, a story I'll relate next.
I lived and worked as a charter fishing guide in the southwest and used the GPS on the rivers down south and had my own farm down there marked as a way point.
I was staying in
Perth at my mothers place while undergoing the course in Sept 2001. I had her place marked as a way point.
I had been away before hand up north to
shark bay and dirk hartog island etc with a group of guys fishing & had way points on Dirk Hartog Island marked also.
The GPS had an electronic flux
gate compass in it also.
While at the course we could do fun things with the GPS like - fix our position and plot a course to say Dirk Hartog Island, press the menu "Go To" and it would point the directional arrow north and give the distance left to go to get there.
Likewise I could plot a course to
Nannup - where we lived or the Donnelly river for some of my fishing spots, press "go to" - and that directional arrow would point south (from our position in
Perth) and give the remaining distance.
You realize how fantastic that is when you've been in class all day poring over charts with compass and parallel rule, dividers etc and plotting courses on charts manually taking magnetic bearings and converting the to true readings to plot on the chart etc..
A GPS really is appreciated when you do all that manually with chart and compass - because it does it in only seconds, what takes perhaps 20 minutes manually.
So..
That night of 9/11 (Sept 11 2001) I've been up late finishing my charting homework for tomorrows course and the plane fly's into the WTC tower on the late TV news! Mum comes and gets me and says - you have to see this, it's unbelievable - there's been some terrible accident and a planes flown into a skyscraper in New
York - its on the telly!
So I am watching the reports and replay of the footage etc - when lo and behold a 2nd plane flys into the 2nd WTC tower.
Well - I'm no ones fool - and start thinking - "this is no accident - I wonder what the Yanks are doing in response now - will they loose a nuke at someone?"
The I remember the Etrex summit GPS in my pocket!
I think back to my experience during Gulf War 1, (next story) and how when I mentioned it to people after the fact, they laughed and said I musta imagined it - & wouldn't believe me!
So I go outside and turn on the GPS!
No problem - I can find where I am. I'm at the waypoint for mums place in
Perth OK!
Like during the day, I picked a way point up north on Dirk Hartog Island and press "go to"!
The direction needle is pointing due SOUTH (like to
Nannup where I live) and giving me about the right distance for Dirk Hartog Island, but 180 degrees the wrong direction.
I figure that's mighty weird - but it's what I suspected because it reflected my experience offshore during the Gulf War 1 invasion.
To check it out - I did another go to - only this time the way point was my farm 300 kms south of us! I press "go to" and NOW
the needles pointing due NORTH (to Dirk Hartog Island - not SOUTH to
Nannup where I lived), BUT the distance displayed is about right for the Farm in
Nannup at about 300 km's!
So I "proved to myself" that the Yanks can reverse readings from their GPS satellites by 180 degrees when they consider themselves under attack. It stops any other power from using GPS guided munitions against them.
Their own military have a built in correction factor for their ships planes and munitions that automatically "corrects for the deliberately altered GPS signals".
The 180 degree reversal - would send GPS guided munitions in the opposite direction from that intended by the attacker while US launched guided munitions planes and ships etc - would automatically correct for it.
Now back to Gulf War 1 where the first occasion of me seeing this phenomena at work occurred.
I forget what year it was, but it was
well before 9/11 and before Gulf War 2 with Colin Powell, it was Gulf War 1 under Stormin Normal Swartzkopf.
Mate a
mine had a 19 ft glass boat with a GPS on board and invited me out fishing off the south west coast at
Hamelin bay!
GPS was only new back then I'd never seen one much less one on a boat with moving charts etc
No problem away we go.
He sets up the GPS and all is
well - we get out Westward past Hamelin island and head south - towards
Augusta keeping the south
west cape on our left (to our east).
The GPS shows us doing just that!
We get to a fishing spot, found on the sounder and drift for a few hours catching the odd fish and listening to the music on the radio.
That's when the news broadcast that the Yanks had invaded Iraq for the first time, kicking Saddams troops outta kuwait eventually!
Yeah so? I'm fishing off the southwest of WA - like I could care less what the yanks are doing half a world away!
It's now after lunch sea breeze building - time to go home.
Bit trickier getting home, the sun glare off the
water and a few reefs we threaded our way out thru, near Hamelin island on the way out, make it a bit harder getting back, than getting out there in the morning with the sun behind us and
water clear so we can easily see those reefs etc.
No problem says the skip - we will just follow our mornings trail/ route on the GPS back to the
boat ramp!
So - turn it on and yes it finds our position but there was a much longer time delay getting a fix than on the way out!
We now have the SW Cape visible still on our Right this time (i.e still to our east by the compass) and away we go - headed back north towards HAMELIN ISLAND - where we launched from the
Hamelin Bay ramp that morning.
Mate says to me - hey look at this?
I look at his chart plotter GPS, and there's our route from this morning - only we aren't following it at all. According to the chart - we are headed due south towards Antarctica - according to the GPS and the breadcrumb trail we are leaving on the chart!
That's weird I say - the compass shows us headed north, we know the land is on our right or by the compass to the east of us as it should be & I can see Hamelin island ahead of us where it should be to our north - why is the GPS chart plotter showing us headed to Antarctica?.
Skipper is scratching his head and admits he doesn't know why. he's never seen it do that before.
So I steer north towards the island we came from that morning, while the mate fiddles with his GPS chart plotter. He tried everything - turning it off - turning it on again, to get a new fix - then call up the mornings route that he saved and sure enough according to the chart and GPS we are headed south past
Augusta towards Antarctica - if the GPS and electronic chart are to be believed - while I am steering north via the compass and my land bearings on the Island & the land is where it should be to the east of us.
Then he posed me the question.
"I was planning to run 30
miles off the coast this morning out of sight of land - I only took us here in sight of land because it was less fuel and shorter trip home if the sea breeze kicked up early which it did!"
"What would we have done IF we were out of sight of land - and the GPS had told us to turn around and go the other way?"
He reckoned he would have followed the GPS coz that's what he always does. Had we done so, we'd have run out of fuel somewhere in the southern ocean between Australia and Antarctica!
I on the other hand rationalized that I'd have steered North east by the compass (opposite to our southwesterly track in the morning) - until we saw land (Australia) and a land mark we recognized to get our correct bearings.
We agreed my plan was the better one - because anything (including the yanks messing with their satellites) could have put the GPS chart plotter on the fritz, while it would have taken a global pole reversal to mess with the compass by 180 degrees!
We got home - but it was my first lesson never to fully trust GPS!
The warnings are on the box about only ever using your GPS as a "backup" for very sound reason. If you have ANY reason for ANY moment not to trust your GPS by what your eyes are telling you - then for goodness sakes - take a moment and check it with the compass - the sun or stars if you have too.
Facts are you can't always trust a GPS.
I've given 3 real world examples of why not.
I have a similar real life tale about when our 2 satellite phones stopped working for 4 days over
easter one year we were offshore at the Houtman Abrolhos Islands - if anyone's interested. (It wasn't the handsets AND it wasn't the satellites either).
Just like you can't rely on your GPS for your primary navigation tool, - you also can't rely on satellite phones as your ONLY emergency rescue tool - maybe carry a personal locator
beacon and a
HF radio as
well.
As for keeping maps and charts up to date that's the mariners (navigators) responsibility, in the case of marine charts there are notices to mariners issued as alterations occur and it's the chart owners responsibility to note these and keep the chart up to date.
The same onus rests on Map users.
Now - do i need to go into the differences between northern and southern hemisphere compensated compasses for anyone?
Did anyone learn anything?
Was it just a waste of my time and effort - as I suspect?
Cheers
FollowupID:
648958