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Old 27-01-2013, 23:25   #1
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True or Magnetic for Electronic Nav

I understand that most if not all PC or IPAD nav programmes / apps give you the option of giving you all data in true or magnetic.

If using electronic nav aids, but still preferring to steer a course via an old fashioned compass - then you should choose to have everything on your electronic gadgets read out in magnetic to save having to apply local variation for course to steer....right?

And for those of you that sail offshore, what is your peference?

Perhaps silly questions, but am just interested in whom does what.
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Old 27-01-2013, 23:29   #2
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Re: True or Magnetic for Electronic Nav.

Perhaps you might run a search on the forum, there have been extensive discussions covering this topic.
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Old 27-01-2013, 23:49   #3
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Re: True or Magnetic for Electronic Nav.

Quote:
Originally Posted by captain58sailin View Post
Perhaps you might run a search on the forum, there have been extensive discussions covering this topic.
I have. Perhaps you might like to provide thread links because, granted, there are plenty of discussions about electronic nav aids, I can not find any with this specific question as a topic.
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Old 27-01-2013, 23:59   #4
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Re: True or Magnetic for Electronic Nav.

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True magnetic ipad inavx course steer compass
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Old 28-01-2013, 00:54   #5
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Re: True or Magnetic for Electronic Nav.

->TVMDC true virgins make dull companions
At the end of the day you are relying on a proper chart to confirm the fixed and variable errors of your location, steering compass, neighboring equipment (off and on) and installation.
You can do this by taking transits of natural ranges to identify errors

With the electronic magic, much better to use True presentation to verify your errors, then you can easily monitor your compass for those errors
->CDMVT can dead men vote twice
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Old 28-01-2013, 00:57   #6
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Re: True or Magnetic for Electronic Nav.

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->TVMDC true virgins make dull companions
At the end of the day you are relying on a proper chart to confirm the fixed and variable errors of your location, steering compass, neighboring equipment (off and on) and installation.
You can do this by taking transits of natural ranges to identify errors

With the electronic magic, much better to use True presentation to verify your errors, then you can easily monitor your compass for those errors
->CDMVT can dead men vote twice
Sorted then. "True" it will be for the electronic nav aids, converted via TVMDC for my course to steer.

Thanks.
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Old 28-01-2013, 02:15   #7
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Re: True or Magnetic for Electronic Nav.

I typed in compass courses into the search and several threads came up, that would address your question.
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Old 28-01-2013, 02:41   #8
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Re: True or Magnetic for Electronic Nav.

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I typed in compass courses into the search and several threads came up, that would address your question.
Yes found a few using that. Many thanks.
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Old 28-01-2013, 03:14   #9
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I recall the overriding technical issue is that the charts are best displayed in a true coordinate system as the magnetic coordinate system varies over the extents of small scale charts. Same with computations such as BTW. Problematic to define in magnetic coordinates over long distances. Should the plotter use the variation at the ships position, the first waypoint, the end waypoint, etc?

That's the format of the typical obsolete paper chart.

So best to apply the variation elsewhere. I tend to keep all my instruments in magnetic as I prefer steering by the old oily compass. Plus the variation around here is near zero.
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Old 28-01-2013, 05:15   #10
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Re: True or Magnetic for Electronic Nav.

I use the magnetic setting on my electronic charts so they (sort of) match the compass.

I have never spent a lot of time thinking about doing it any other way.
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Old 28-01-2013, 09:19   #11
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Quote:
Originally Posted by Kiwi399 View Post
I understand that most if not all PC or IPAD nav programmes / apps give you the option of giving you all data in true or magnetic.

If using electronic nav aids, but still preferring to steer a course via an old fashioned compass - then you should choose to have everything on your electronic gadgets read out in magnetic to save having to apply local variation for course to steer....right?

And for those of you that sail offshore, what is your peference?

Perhaps silly questions, but am just interested in whom does what.
Unless you are regularly plotting on paper charts and using the True Heading data from your Electronic Chart plotter to do it, it makes no sense to display true heading.

You don't steer true course, you steer magnetic course using a compass mount near the helm. So why would you display a true heading on you chart plotter?

For those of you that are concerned about the chart plotter failing and having to revert to paper, you can convert to True for plotting of your last known magnetic bearing or simply use the ship's compass and convert your current magnetic bearing.

Just my humble opinion.
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Old 28-01-2013, 09:32   #12
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Re: True or Magnetic for Electronic Nav.

It's a hard question, and many valid points pro and con have been made here.

It's a dilemma because you're either out with your charts or out with your compass.

I sailed for so many years with nothing but a compass, that this tends to be my mental starting point with everything. Also, it would be really confusing to display heading and autopilot information in true. So, I use magnetic with my electronic systems and back out variation when I plot anything on my paper charts.

Variation is very consistent where I sail and amounts to less then 2 degrees, so it's not all that hard, but I recognize that in other areas of the world this could be a real PITA.
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Old 28-01-2013, 09:35   #13
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Re: True or Magnetic for Electronic Nav.

It does not matter as long as your are consistent with what you use. Given boats typically have magnetic compasses and not gyros, magnetic is probably a little more convenient if you reference everything to magnetic.

With charts you would obviously use the magnetic circle in the compass rose.
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Old 28-01-2013, 10:18   #14
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Re: True or Magnetic for Electronic Nav.

I set everything to show magnetic bearings.
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Old 28-01-2013, 11:44   #15
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Re: True or Magnetic for Electronic Nav.

The only problem with using Magnetic is your deviation may change radically with a change in heading. If you want to split hairs, you should have a compass deviation card that you can refer to. This is especially important with steel boats, but there is often enough steel present on a glass boat to make a difference. Anyway, because of the changing deviation, as opposed to variation which will be the same on any heading for a given position, the difference between True and Magnetic will be different, depending on which way you are pointing. That would appear to present a (minor) problem, wouldn't it?

You can adjust out most of the deviation in your compass, though, but it can be a frustrating exercise if you don't know exactly how to do it, or if you have a dinky little compass and a typical small boat installation. You can download HO226, the Handbook of Compass Adjustment, in PDF though I must warn you it is a bit dry and technical. The final step is of course to construct your deviation table.

HOWEVER, we are talking about sailboats, which can have a tremendous amount of leeway into which three or four degrees of deviation can simply disappear. For taking bearings, though, it can be significant. So YMMV.

Personally, I do everything in True, because that is how it is done aboard ship. And because True North happens to point precisely to where all meridians converge at the true pole. Everything just makes a lot more sense when you look at the big picture, to me, anyway. It is simple enough to refer to your variation and deviation and convert to a course to steer, or more importantly, to convert a visual magnetic bearing to a true one. On a ship, a gyrocompass is used, and the only error is gyro error, typically a degree or less. We only use the magnetic compass to check against the gyro and in the event that the gyro quits working. So there are no issues of convenience for us, using true, while it could be seen as slightly more convenient on a sailboat to use magnetic.

But is it a bad thing, to use Magnetic? On a sailboat, not really. Especially if you cruise in one small area.

I guess it is really a personal preference thing. And it isn't an earthshaking big deal if we disagree. Do it how ya feel it.
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