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Old 24-11-2011, 02:16   #1
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Electronic Charts

I have been wandering if anyone is using Navionics charts on iPad or smart phone.
Do they automatically adjust your bearing ( on real chart you have to calculate deviation).
I have downloaded to my iPad and looks good (zoom in, tides, marks.....).
Not sure if I can use it when I have no Internet coverage.
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Old 24-11-2011, 06:11   #2
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Re: Electronic charts

I use these charts on an Android, but I'm not really sure what you are asking.

What do you mean by "automatically adjust your bearing"?

Don't know if this helps but there is no deviation as its not a fixed piece of equipment. Same as there's no deviation calc when using a handheld compass for bearings.

You don't need an internet connection for the basics such as position, cog, sog, bearings etc. But the accuracy and speed of gps derived info updates is very much down to the device you install this on. Take note....the devices available are not all equal in this respect.

You will need an internet connection to download grib file overlays etc.
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Old 24-11-2011, 16:10   #3
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Re: Electronic Charts

When i use printed chart for passage planning i transfer my heading into printed compass. in Melbourne i have adjust my heading about 12 deg. This is diavetion required to obtain true heading (say my heading is 45 deg minus 12 deg, so my true heading will be 33 deg). Not sure if electronic charts are have this calculated automaticaly.
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Old 24-11-2011, 16:33   #4
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Re: Electronic Charts

What you are referring to is called variation. Deviation is the error caused by the compass or equipment around the compass. In the Navy, we used the formula CDMVT add east when solving Compass to True heading

Compass reading
Apply Deviation error
This yields Magnetic heading
Apply Variation error and always add east variation
This yields True heading

Hope this helps understanding your request.
Bruce
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Old 24-11-2011, 16:39   #5
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Re: Electronic Charts

Part of the above problem is the definition of the words. There are 3 kinds of bearings: true, magnetic, and compass bearing. Maps use True North (pointing to the North Pole.) Your compass points to magnetic north and the difference between that and true (in your area 12 deg) is the "variation" so the calculation you are making is to convert the "True" heading (from your map) to your "Magnetic" heading. Often that is enough for many boats. The third type of bearing is "Compass" and that takes into account the "deviation" which is caused by the magnetic properties of the boat (this is only for fixed compasses and can not be calcualated to hand held or compasses that can move around.) You are probably ignoring this calculation. I do since it's less than 2 deg. and I can't really steer closer than that anyway.

Now back to your original question.... I have no idea. But I do know that using Navionics charts on my Raymarine can convert from True to Magnetic automatically. I have just ordered an iPad so I do hope it will do the same thing.
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Old 24-11-2011, 16:46   #6
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Re: Electronic Charts

Bruce, you answered quickly while I was typing my long lecture.
When I took the British RYA Yachtmaster course their suggestion for remembering was TVMDC (True - variation - magnetic - deviation - Compass) or True Virgins Make Dull Company. And to remember whether to add or subtract the variations include "AW" At Weddings (Add West.).
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Old 24-11-2011, 16:57   #7
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Re: Electronic Charts

That is another great way to remember the conversion. When converting from true to compass we add west variation and subtract east.
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Old 24-11-2011, 17:12   #8
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Re: Electronic Charts

Ahhh, ok now I understand.

Then the answer is no.

Everything on the device is 'True'. There is no magnetic compass within the device to establish 'magnetic'.

Think of it as the same as a paper chart. You must manually apply an appropriate variation to get magnetic
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Old 24-11-2011, 17:22   #9
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Re: Electronic Charts

Quote:
Originally Posted by jim_thomsen View Post
........using Navionics charts on my Raymarine can convert from True to Magnetic automatically. I have just ordered an iPad so I do hope it will do the same thing.
I think you will be disappointed. The reason that you can do it with your Raymarine system is because somewhere in that system there is a fluxgate compass from which to get magnetic compass information. I would doubt that the iPad would have a magnetic compass of any kind inside....but I'm just guessing here.
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Old 24-11-2011, 17:48   #10
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Re: Electronic Charts

ipad has a compass in it.The 3G version has a GPS as well

Dave
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Old 24-11-2011, 18:39   #11
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Re: Electronic Charts

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Originally Posted by goboatingnow View Post
ipad has a compass in it.The 3G version has a GPS as well

Dave
Wow, that's clever........ Which kinda throws my earlier rationale out the window doesn't it.

But I did just check on the Navionics website and they do say that the bearings etc are all True. So there doesn't seem to be any functionality to generate Magnetic within the app (yet?).
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Old 24-11-2011, 19:02   #12
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Re: Electronic Charts

you dont need to warry about variation or deviation with navionics on ipad

you dont need internet, it works via the inbuilt gps

you do need a backup plan in case the battery goes flat
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Old 24-11-2011, 20:37   #13
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Like any decent integrated instrumentation, the iPad will get the variation from it's GPS module (every modern GPS can tell you variation for your location).

Also, iPad and iPhone both have compass, gps and 3D accelerometers aboard. But for the iPad you need the "3G" version with the SIM card slot and the black plastic antenna cover on the back.

I'm pretty sure the Ipad nav programs can give you magnetic course to steer... Check out settings!

cheers,
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Old 24-11-2011, 21:46   #14
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Re: Electronic Charts

I don't think the limitation is the device. The Navionics app itself doesn't seem to deal in magnetic at all, or address variation.

From the Q&A section on their website.

Q. Does the Navionics mobile app use magnetic north or true north
A. Navionics mobile app currently uses true north.
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Old 29-11-2011, 13:16   #15
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Re: Electronic Charts

I used the Navionics app on my iPad this past season and was mostly happy. I wish there was a "navigate to" function where you could just touch a point on the chart and get guidance to it. For now, the route planning works, it's just takes a bit longer.

I previously used OpenCPN on a netbook with a Garmin GPSMap 76cs+. Now I keep the Garmin onboard as backup and for use in direct sunlight (iPad screen is hard to read in full sun) and wet conditions.
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