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Old 14-11-2017, 10:33   #16
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Re: Another plotter assisted grounding?

Someone that can read the water or is keeping an eye on other instruments can help in many situations.
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Old 14-11-2017, 10:44   #17
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Re: Another plotter assisted grounding?

There is a problem with a vector chart that every navigator should take note of.
A raster chart is a 'photocopy' of paper charts. So you can guarantee that the information will be correct as at the latest correction as will your own paper charts.
Vector charts are those which have been compiled from raw data and are subject to any errors that the compiling process may have. They are produced in layers so that you can zoom in and zoom out at will. Now if you zoom out too far for the environment that you are in, you can miss a hazard which will be shown on the raster chart. There are many cases of ships and yachts which have run aground because of the incorrect use of the vector charts. As long as you understand this issue than all will be well.
A few years ago I heard that a US warship ran aground in the Philippines on a reef and was totally wrecked. The reef was 8 miles from where the chart showed it to be.
As always when you are navigating, one piece of information is not enough. You should have a minimum of 2 but preferably at least 3 means of independently plotting your course and position. Pre GPS, when I taught navigation and pilotage I showed that there were at least 20 different ways of fixing a ship. A DR and EP record in the log is a must.
I always plan my passage roughly first on a chart, then use my electronic raster charts to electronically confirm my passage. Then I can transfer the waypoints to my vector plotter.
I don't think that there are raster plotters because of the limited methods that they give for electronic manipulation.
Just be aware of the limitations of the tools at your disposal, and remember that when the batteries go flat or the plotter crashes, then you will be glad of the DR/EP that you have recorded. Add that to a printed list of waypoints and you have a really good backup.
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Old 14-11-2017, 14:57   #18
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Re: Another plotter assisted grounding?

The technical jargon for this sort of thing is....IIE

IIE Instrument Induced Error.

Surely anyone who navigates based on the info from a bit of electronic equipment alone with no other support source (eg sounder etc etc) is a bit silly!
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Old 14-11-2017, 15:08   #19
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Re: Another plotter assisted grounding?

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The technical jargon for this sort of thing is....IIE

IIE Instrument Induced Error.

Surely anyone who navigates based on the info from a bit of electronic equipment alone with no other support source (eg sounder etc etc) is a bit silly!
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Old 14-11-2017, 18:23   #20
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Re: Another plotter assisted grounding?

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With references to relying on charts, paper, raster, or vector, I got a lesson six months ago about the accuracy of US Coastal Charts in little-used waters. Entering Doboy Sound in Georgia, I found the charted depths to be wrong by at least 7 feet. I came within 3.5 feet of grounding, and it wasn't an isolated shoal - I was seeing 3.5 to 5 under the keel for about a mile. Minimum depth, per the chart was 13 feet at low tide, but at a little more than half tide, I was seeing 3.5 feet under the keel, so 9 feet. Since tides in that area are 7 feet and more, at low tide I would have grounded. I later check my paper chart to see if there was any discrepancy with the chartplotter, but two different chart software and the paper chart matched exactly, and all three had been updated within two months of the trip.

With the budget cuts to NOAA, I don't expect the situation to improve in the US any time soon, so I stick to channels I know are maintained or ones where I know they get a lot of traffic and I have local information. Maybe the captain of the patrol boat was following the chart, doing everything right, and the chart data was out-dated.
Glad someone has raised the other big issue that is putting boats on the rocks.

Inadequately surveyed areas contain hazards and depths that are not on the charts or are not shown in the correct position.
We need to know how well surveyed each area is or apply big safety margins.Paper and raster charts have zone of confidence or reliability diagrams. Vector charts will often show completely unsurveyed areas, however, areas of low confidence often appear just like fully surveyed areas. Density of soundings shown on the chart is one sign of survey completeness.
Dave
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Old 14-11-2017, 18:43   #21
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Re: Another plotter assisted grounding?

It nearly happened to me--but I realised that the GPS system had not been properly set to the chart plotter--and this has to be done. It was about one hundred metres different--so you need to do three things before setting out. Most marinas have a setting point where an accurate lattitude and longitude is available. Some harbours have a compass adjustment bouy for swinging a compass, and its position is accurately logged. Make sure your chart plotter agrees with this position, and that your GPS does too.

While you are at it--if your boat is steel--it might be a good idea to swing your compass and have it properly adjusted.

Oh--and also ensure that your fluxgate compass is not restricted or has any unshielded and unscreened wires capable of carrying current anywhere near it. One person I knew set his autopilopt, went below and used his radio transceiver. The next thing he knew was his new catamaran ran aground on a reef and was a total loss. Some idiot, when installing the compass, placed it so that the power wire for the tranceiver was almost in contact with it.
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Old 14-11-2017, 19:27   #22
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Another plotter assisted grounding?

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Because for damn sure we do not what any humans reading our charts. It's the humans that are worthless. They should stay on land and let their chartplotters send them video they can post on youtube.


Vector charts are equally or more readable by humans.. why use old technology? Maybe we should all go back to using FAX.
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Old 14-11-2017, 20:35   #23
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Re: Another plotter assisted grounding?

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It nearly happened to me--but I realised that the GPS system had not been properly set to the chart plotter--and this has to be done. It was about one hundred metres different
I've said this before...

An error of 100 meters in the GPS or chart should never be an issue when navigating near charted hazards for the simple reason that you should never be relying upon such accuracy to avoid the hazard. Give the bloody thing enough offing so that such errors will not lead to grief. If it is a visible hazard, visual checks can allow closer passage, but when relying upon charts and GPS, adequate clearance is essential.

Jim
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Old 14-11-2017, 20:52   #24
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Re: Another plotter assisted grounding?

And I don't think we should enter unsurveyed areas at night. Your eyes can't help you see "bumps" waiting for you. If it says "unsurveyed", heave to, wait, re-trace your steps where you know it is safe, and wait for tomorrow, or until you have visibility or can pick a safe route to a new destination. Those options would have saved the cat in the Kimberleys.

Honestly, it is possible these guys were going too fast for the conditions. It was 1 a.m. Although, I suppose it could also be correct that they had an equipment failure. We once had a SatNav fail by giving ever worse fixes. Equipment, especially new, can have the hated infant mortality, too.

What a shame to wreck the ship.

Ann
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Old 14-11-2017, 22:46   #25
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Re: Another plotter assisted grounding?

Had a taxpayer supplied vessel come into Myora a few weeks back.
Had two attempts at crossing a drying sandbank to gain access instead of going 40 metres and around a cardinal where its deep enough for our 6ft draft at low tide.

They came in to make sure others weren't damaging the environment they just chopped up with their props.
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Old 15-11-2017, 04:37   #26
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Re: Another plotter assisted grounding?

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Originally Posted by mikecambrai View Post
I don't think that there are raster plotters because of the limited methods that they give for electronic manipulation.
???

Our plotter let's us choose raster or vector charts.

And we also use an Android app that presents raster charts...

???

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Old 15-11-2017, 07:07   #27
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Re: Another plotter assisted grounding?

I exclusively use raster charts. I don't understand why people are saying raster charts are useless. IMO they are better / safer than vector charts because of the Zoom issue.. things don't magically appear at different zoom with raster and I still do my weather routing, overlay AIS and Grib, etc.. I agree that the technology exists to warn navigators that your route goes into shallow water and even alarm if you are sailing into shallows. This was discussed extensively when team Vestas wind ran aground last Volvo race. The chart plotter makers say they won't add the safety feature due to liability and the expectation that the software will always tell them 'danger ahead'. It is a great example of how individuals suing companies hurts the general consumer and has gotten out of hand, especially in America IMO.
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Old 15-11-2017, 07:44   #28
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Re: Another plotter assisted grounding?

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I've said this before...

An error of 100 meters in the GPS or chart should never be an issue when navigating near charted hazards for the simple reason that you should never be relying upon such accuracy to avoid the hazard. Give the bloody thing enough offing so that such errors will not lead to grief. If it is a visible hazard, visual checks can allow closer passage, but when relying upon charts and GPS, adequate clearance is essential.

Jim
Jim, it stuns me that people have to be told that! But they do. I read these"chart plotter assisted" comments and just don't get them. It's just a tool, like a paper chart is. I never 100% trust a chart until I've proved it correct.

On another forum I was told recently I"I worry to much" if that means I'm cautious, use multiple navigational devices, including the my eyes, ears and gut, well I guess I am.

When entering an anchorage once with a young crew I was mocked for going in slow when the chart showed no dangers, my reply was "you speak like a man that's never hit anything".

Chart plotters have made cruising safer, I'm not sure that the dumbing down of society has made cruising safer!
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Old 15-11-2017, 07:45   #29
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Re: Another plotter assisted grounding?

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Originally Posted by JPA Cate View Post
And I don't think we should enter unsurveyed areas at night. Your eyes can't help you see "bumps" waiting for you. If it says "unsurveyed", heave to, wait, re-trace your steps where you know it is safe, and wait for tomorrow, or until you have visibility or can pick a safe route to a new destination. Those options would have saved the cat in the Kimberleys.

Honestly, it is possible these guys were going too fast for the conditions. It was 1 a.m. Although, I suppose it could also be correct that they had an equipment failure. We once had a SatNav fail by giving ever worse fixes. Equipment, especially new, can have the hated infant mortality, too.

What a shame to wreck the ship.

Ann
100%.....isnt that obvious to?
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Old 15-11-2017, 09:31   #30
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Re: Another plotter assisted grounding?

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This was discussed extensively when team Vestas wind ran aground last Volvo race. The chart plotter makers say they won't add the safety feature due to liability and the expectation that the software will always tell them 'danger ahead'. It is a great example of how individuals suing companies hurts the general consumer and has gotten out of hand, especially in America IMO.
Which is daft as there no more liability than adding an accelerator pedal to a car. And in any case liability where? Cruisers will be all over the world in different legal systems. MFD manufacturers likewise are based in different countries.

I had never used a MFD chart plotter before I bought my boat, but it was obvious to me that some detail would need zooming to see. I can say I do zoom in 100% of the time though, only as much as I deem necessary.
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