Magnetic vs True North for Electronic Nav Instrument Setting

It's interesting to think about how things evolve, if I may use that e word. True North and Magnetic North have both been used for a long time and in general both served their purpose.

The original North direction was the north star, Polaris, before magnetic compasses. And of course, the North Star gives true north, as well as the time of day as Ursa Minor rotate around Polaris. And Portolans/charts were drawn in True North, if any geographical reference is used since that's all that was known.

So around the 12 century, the Italians started using the compass. Yes the Chinese knew it for centuries before, but apparently it was discovered in the West in Amalfi/Italy, and thence to the Arabs, since the Arabic word for compass refers to the Italians. So now navigators noticed that the compass didn't point at Polaris. Since the compass was always at hand, charts started using Magnetic, but were still plotted in True North.

Charts were still drawn to True North, because that's the way the Earth is. The French did a very complete job of determining the correct orientation of Europe with respect to the rotating axis of the globe not to the compass reference. Though of course the chart makers understood how the compass pointed and gave us charts such as the one Bob has shown above, indicating magnetic variation worldwide.

This carried on down until inertial navigation was developed during and about WWII. Since one needs to account for the rotation of the Earth in the inertial equations, True North was required. And the Gyro Compass gave True North. And now we have ships and planes navigating using Inertial Navigation, and each one also had a magnetic compass for backup. And you can bet your fanny that both systems were well understood.

Now in the last 1/2 century, Loran and then GPS come along and gives absolute geographic position, a great advance, and thus inherently gives the velocity and destination vectors in True North, with the option of Magnetic North if that's what you want. And that's still well understood, even though there certainly have been some screwups.

Each group of navigators selects the North reference that's correct for them. If you're launching rockets, True North it is. If you're piloting a sailboat around Narragansett Bay, you'd probably use Magnetic. And navigators truly understand this.

So to say everything is a mess simply isn't true. It's not that complicated once you understand what's going on and you'd better understand the reference frame (True or Magnetic,) that you're using, but it's not a mess. It may be a little hard to understand when first introduced (TVMDC, anybody?) but it's well understood.

I mention that the original question is "do you prefer True or Magnetic?" And one has to understand both references to honestly have a choice. BTW, I don't care, just tell me which it is.

Boris
 
This is really interesting. I think I am liking True more and more. Looks like it might be less hassle over the long run. Less change, less variance and Less calculating.

You all are a really "straight up bunch" :wink: :lol:

Harvey
SleepyC :moon
 
Harvey, When you say...Less change, less variance and Less calculating

You are actually talking about Magnetic north. That is the simpler navigational reference that does not require any local or regional adjustment.

The "adjustment" to magnetic referred to above relates to you choosing a setting on a device that defaults to true such as GPS and the "adjustment" is you picking a setting. Don't worry about the default, just make a choice. Do you want to think about whether your compass and devices are all agreeing on the true north declination offset or do you want to just set everything to Mag and forget about it? Do you plot courses on paper maps? If yes, then you need to find the declination offset on the map and set any devices of compasses that you are using to match it and confirm that again with each physical map you use. That task is not hard once you are familiar with adjusting your devices but it is just one more thing to manage.

Magnetic is how a compass points with no intervention by the user to do any correction for anything (with correct installation). That is the least work or trouble and requires no calculations.

True = Magnetic, plus or minus the declination which changes over time and by location as you travel.
 
Boy does this thread illustrate the knowledge and helpfulness available on this site...and with not an iota of snarkiness. What pleasant thing. Once again thanks to Bill and Mike for the site and for the members thereon....and for the basic rule!!
 
Aurelia,

Please check your definitions. I believe you might have them backwards.

True is the way the Earth is. All True North directions lead to the North Pole, defining the axis around which the Earth spins. It has been a constant for the life of the Earth.

Magnetic is the way the compass points. As shown in Bob/thataway's map above, the compass points in different directions at different points on the Earth. And even worse, that varying direction changes with time.

Nothing wrong with choosing Magnetic as the heading, but one has to make sure you're using the correct corrections: difference between True and Magnetic and any errors inherent in the compass itself.

The charts of the Earth are laid out to represent the actual geographic relationship, the truth, from whence the appellation "True" is derived. So, when you're going from one place to another, you are using the True course. Magnetic is just using a compass to measure an approximation of True.

The compass was and is a big step forward, but it's a measurement instrument, and doesn't change the way the Earth is. The same may be said for GPS, but it has better accuracy.

Boris
 
We are on the same page Boris. That is part of the trick with north references, they are confusing and the mixture of terms being tossed around makes it hard to keep them straight. I am a GIS professional and instructor by trade and address related questions on a regular basis.

I am a map person and regional GPS specialist so True has its place for me. But when managing a blend of humans, devices, and communication between them all, I recommend magnetic to most folks.

Greg
 
I just use my GPS's and keep the boat in the blue part and going in the direction I want to go. If'n for some reason my eye or radar differs from what the GPS says, I'm going to place more faith in my eye and/or radar. :)

For all practical purposes, most times I don't even really need to know what direction N is except for the brief periods of time when I transition from not moving/moving slower than the current to moving. E.g. it's useful to know what direction to point the boat until the gps indication of direction is accurate. After that, I just keep it in the blue and pointing where I want to go. This is a fun and interesting discussion, but I would claim true vs magnetic is of little import when it comes to how most of us use the GPS in practice.
 
Right you are Roger. A more important factor might be how you set the safety depth on your chartplotter map display to make sure when you see blue, it really should be blue enough for your boat.

Greg
 
rogerbum":1le6kdli said:
I just use my GPS's and keep the boat in the blue part and going in the direction I want to go. If'n for some reason my eye or radar differs from what the GPS says, I'm going to place more faith in my eye and/or radar. :)

For all practical purposes, most times I don't even really need to know what direction N is except for the brief periods of time when I transition from not moving/moving slower than the current to moving. E.g. it's useful to know what direction to point the boat until the gps indication of direction is accurate. After that, I just keep it in the blue and pointing where I want to go. This is a fun and interesting discussion, but I would claim true vs magnetic is of little import when it comes to how most of us use the GPS in practice.
Click to expand...
+1
My thoughts exactly Roger. But still, a truly informative discussion. :thup

Peter
 
This is getting really good. At first I was thinking Greg had switched the terms. It makes sense that with Magnetic as the primary setting, declination only changes the orientation of the charts. Then what Boris says about True makes some sense too.

I have the feeling it is going to come down to what the electronics guys at Rogers Marina decide, because it sounds like it will be dependent on what the participants on the electronic community on SleepyC can do to get along.

This is a really interesting thread. Thanks to all for all the enlightening comments. I am learning a lot.

Harvey
SleepyC :moon
 
So after going over this thread several times, and talking with several knowledgeable folks in my area, I am considering strongly that setting everything to magnetic may be the best move. (At least for the electronics) and I can tilt the paper when I need to to get the same picture. Truth is that the electronics are all showing course up or heading up anyway. (There is another one for consideration.) Does either course or heading have any advantage over the other. I don't often run a course, so generally use "heading up" for the MFD and now it is available on the AIS as well so both of those screens look the same.

Another twist.

Harvey
SleepyC :moon
 
I like magnetic, and course up - the chart image doesn't keep shifting around as much as with heading up.

If I'm not following a course, my chartplotter defaults to heading up (track up, actually - based the direction I have been going, not where the boat is actually pointing). Don't have an electronic compass feeding heading to the chartplotter, or an autopilot holding me on course. Maybe I would choose differently if I did.

My Radar (stand-alone, not integrated on the chartplotter) displays heading up, in keeping with the idea that Radar shows what is - what I might be able to see if I looked straight ahead. Seems to make sense to me, or maybe I'm just used to it that way.
 
The reason to use "heading up" is that the radar will overlay accurately--with the new chart plotters at 10 HZ this should be accurate. The heading up is the direction the boat is traveling at that instant (10x minute sampling time, and of course will vary).

"Course up" is toward a waypoint--this may or may not be what your current heading is. If you have not set a way point, the GPS will probably revert to "heading up".

Because "course up" or North up, is a stable geographic point, the chart plotter should not move unless you are way off course (cross track error), and then only very slowly.

I use heading up. I want to see what is on the chart, and compare that to what I am visually seeing.

Generally when planing with a paper chart, it is easier for me to use North up orientation--since the Lat and Long lines are square to the chart's North up, and it is then easy to lay a course, and measure the angle with a protractor, without having to go to the rose, and step off with parallel rules.

Yes, there are times when it is nice rotate the paper chart to your course, so you can see what the visual picture will be. The chart plotter makes all of this un-necessary. However sometimes it is still very valuable to look at the paper chart the evening before a day's run, to look for alternate routes, coves, and hazards which you might not notice when looking at the chart plotter or computer.

The new Garmin xs series (1040xs for example) has WiFi built in, so you can interface it with the Garmin Blue Chart mobile, and transfer waypoints and routes directly from the i pad, or a computer. When planing on the i pad, I use N up. I don't know if you can do magnetic courses and then transfer to the MFD--but you can change to magnetic courses on the MFD, after the route is placed on the MFD. If your i pad does not have a built in GPS, the i pad can get position data from the Garmin MFD via WiFi.
 
I keep repeating this, just to make sure that it's clear that True/Magnetic compass reference is different from heading-up or course-up. Your direction will show differently depending on if you're in True or Magnetic. About 14 deg different in SoCal, different elsewhere.

True is geographic North and of course, Magnetic is magnetic North. The difference between Magnetic varies around the world, but True stays true.

Both represent only reference frames in geographic maps, electronic or paper. They're related, but not the same.

Heading-up or Course-up show you a direction within the True/Magnetic reference you've chosen. That is you can have heading-up shown in True or Magnetic, and the chart will rotate to accommodate the direction in the reference you've chosen. And Bob has given an excellent discourse on the advantages or either.

Please don't confuse the direction (Heading/Course) with the reference (True/Magnetic.). Do set the reference in all your instruments to one reference, either True or Magnetic.

Boris

PS: thank God for spell check.
 
Boris and Dr Bob, Thanks for the excellent posts here. This is been a very helpful discussion. I really appreciate all you time and effort spent here, (and not just on this topic but on all of them). My preference has always been to heading up on the MFD, but I have vacillated on the Northerly reference. I am working now on deciding, and will switch everything to one point soon. The quarter is still in the air. Thanks for keeping it spinning :lol:

Harvey
SleepyC :moon
 
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