Something dodgy going on here

[Mothership 6]

Using the GPS to attempt to find the rock was just silly.

 

Using the hull of the boat was downright stupid.

[rigger 47]

FYI, from some recent work that involved monitoring position accuracy of some equipment using GPS reported positions. Of all the recorded observations - inexcess of 1800, the error rate was 0.6% outside our limits, the worst error was in excess of 1000nm. Otherwise all other errors were below 200m.

Observations were in the Auckland area.

[Guest]

200m, safety factor of 5, don't get within 1/2 nm of anything solid relying on GPS(even that seems close to me)

[Murky 1]

So in summary, it's starting to look like:

- it is a navigational system known to be occasionally susceptible to errors

- the prevalence and size of the errors seems to be unpredictable

- the most sensible way to use this navigational system is when you can verify your position by eye.

 

I have loved mine but if the variances are that big and you never quite know when it's going to try and slip through a dodgy reading...it starts to call into question why these things exist.

 

If half a nautical mile is a safe kind of limit...I can do that on my own.

[rigger 47]

Only one error we had was greater than 200metres, without looking up the data which is still being sorted, most of the errors were less than 80metres - the objects were moored with a known maximum swing radius, so part of that 80metres was the swing radius.

 

I believe that the US military is running tests in various locations where they cause GPS data to be out of wack or totally unavailable. Will see if I can find the website that listed the test areas, was in a notice to mariners that I read recently.

[wheels 543]

It is not always the GPS, but often the map. Find a Charted Co-ordinate and then rock on upto it and check how far out the GPS is saying it is. The Long/Lat that is. Don't trust the chart. Although the US can create an "era" in the signal, that is not done much anymore because GPS is old technology for Bomb guidence these days. I have always found the GPS accuracy to be very very accurate. But I have sometimes found the chart to be out in some places and bang on in others.

[Guest Rocket]

All of which explains why the devices are great as an aid but deadly if you don't use your eyes. Looking at the GPS to try and cut a corner? In the olden days we would be up the mast or standing on the bow using our eyes - seems reverse Darwinism is winning - there will be loud exclamations from the nav station downstairs along the lines of "WTF was that?" every time someone sails around obstructions by braille.

 

I would have thought reading the report on the Oz incident people would have taken on board the findings (which were reported on this site and commented on). Seems not - sigh...

 

I have found my way into harbours using radar in poor visibility but would never ever consider entering one by GPS alone - most of the time the safe passage track on the GPS is on a headland.

[wheels 543]

And hence the reason why all of the start with a disclaimer that say's it is not a navigation device and charts should be used.

[Guest]

Same as Rocket. A good radar you know how to read is magnificent and doesn't lie. GPS's do tell porkies.

[Murky 1]

Yes guys, I did get the point a long way back - as evidenced by the fact that my boat is not sunk alongside the Sugarloaf - and certainly the three consecutive posts advocating eye/up the rig, charts and radar have driven the message home.

 

My point was: given the above and knowing that you can never be sure when it's going to have one of its moments, please remind me again what is the purpose of the GPS? How much of an "aid to navigation" is it if you had to find where you were by other means?

[Guest]

please remind me again what is the purpose of the GPS?

So the SIS can track you?

So you have something to spend all that left over money on?

So there was something else to shoehorn into a iPh?

So you can leave the BOI and find Aussie?

So dumbarses can find their way around a Simrad course?

Another way to make the population of today look totally hopeless to anyone from the past.

So Fineline can make lots of pretty lines on a chart yet probably knot follow one of them

So Navman has another instrument to feck up?

And as if we need more, another item to make sure your eyes are on the roads for the minimum amount of time possible while you're driving.

Or for people to damn lazy to work out GMT when calling in a SAR time when going for a fly. Which would be me, hence mine is always set on GMT and feet.

 

There is an outside chance there maybe other reasons as well

 

As an 'aid' they can be very good. The disclaimer on start-up should read -

'This is only a Aid to navigation and will comfortably get you too a few 100 metres from your destination. From there you're on your own buddy as I do have the capability to kill you and yours'.

 

I think you may find handhelds do suffer errors more than bigger more serious units. I've used, or at least had it turned on, the one on Big Steel a lot and it does appear surprisingly accurate. A Lowrance plotter running something 'gold' charts from memory. Every time I've been close to something, even pulling into it's marina or going down the small river by Sanctuary Cove whatever it's called, it has been very spot on. One of the other boats has a older JVC and it's good also. But I still wouldn't trust them inside 200mts given any other options, of which there always are.

[Guest]

The frequency of vessels running aground has increased since the invention of GPS Navigation.

[Grinna 2]

Nothing different from radar. When radar became widely used there were numerous radar assisted collisions. Satellite assisted groundings will occur because people use the technology without necessarily understanding its limitations. They use it and it seems to work fine ..... right up until the point where it doesn't, and then they're in the poo.

[John B 106]

The frequency of vessels running aground has increased since the invention of GPS Navigation.

Yeah, there was a launch came out of the Tamaki river a year or two ago and it hit Rangitoto.

 

That would have been GPS caused that, or some other 3 letter word.

[cam 0]

Yeah, there was a launch came out of the Tamaki river a year or two ago and it hit Rangitoto.

 

That would have been GPS caused that, or some other 3 letter word.

 

 

but those RUM assisted collisions are a bit off topic here I reckon? you can't really blame the technology there, which works very well at it's job AFAIK. Seems a perfectly designed technology to aim launches into Rangi.

[rigger 47]

had a GPS outage / error caused by an Owl,

 

2 GPS units at the chart table with different positions being reported, went onto the bridge wing looked up and there was an Owl perched on one of the GPS antennas.

The Owl stayed with us for a week or two and found the GPS antenna to be the best perch.

[John B 106]

ha .. yeah .. one day on ap hanging over the back of the boat looking at the wake, the plotter did its lost signal wail. My head was over the antenna. I wondered why I was seeing strings of figures with 36 and 175 in them.

 

Parts of the Noisies at the northern end are well wrong on my chart . Thats repeated regularly so I suspect its the chart rather than signal.That goes for the barrier anomalies too I think. It's whatever raymarine has .. Navionics?

[cam 0]

Parts of the Noisies at the northern end are well wrong on my chart . Thats repeated regularly so I suspect its the chart rather than signal.That goes for the barrier anomalies too I think. It's whatever raymarine has .. Navionics?

 

I wonder if this is an area with a survey that had a poor zone of confidence (ZOC).

This ZOC idea is a new term to me, and I only know about it from reading the report on the flinders islet race the other day.

 

"115. In addition to the GPS and chart plotter errors, the hydrographic charting accuracy of Flinders Islet is to within a horizontal distance of +/- 50 metres. This represents the accuracy in an area designated Zone of Confidence (ZOC) B. In ZOC B areas the depth is also only charted to an accuracy of 1 metre + 2% of the depth and although uncharted dangers to surface navigation are not expected they may exist. Most of the coast is ZOC C or higher. In ZOC C the position accuracy is +/- 500 metres, the depth 2 metres + 5% of the depth and depth anomalies may be expected. The zones and definitions are contained on paper charts and some electronic charts in ZOC Diagrams. This means that what is displayed on a chart plotter needs to be interpreted and not accepted as 100% accurate and without error."

 

I understand new zealand surveys (and indirectly the subsequent charts based on them) were classified with a ZOC rating in 2004.

 

I have not been able to find a index of the survey-ZOC rating anywhere yet. I enquired to LINZ about this but have had no reply as yet.

 

All my charts are prior to 2004, I did wonder if newer charts include this ZOC rating directly along with the survey data? Has anyone come across this ZOC data anywhere for NZ surveys/charts or know any more about it?