North: magnetic, true & grid

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North: magnetic, true & grid

Published on Saturday, 05 December 2009 11:51

Written by Holger

When it comes to kayak fishing, it's handy to know how to use a compass for navigation. One of the most crucial aspects of that, however, is understanding the difference between the varying types of north; magnetic, true and grid. If you asked a couple of people in northern Canada where north is, some might point left, others right, and do you know what? They are both right! How does that work? No, not too much grog - there are indeed several different norths...

Magnetic North is the north your compass is pointing to. The north of the earth's magnetic field. Currently somewhere in northern Canada, and moves with about 39-40km per year. {mosimage} True North is the actual north pole, where all the longitudes meet at the top. If you stand on it, wherever you look you're looking south - how cool is that? Grid North is defined by your map's grid lines, normally UTM. The difference between magnetic and true norths is called declination and the difference between true north and grid north is called grid convergence.

You might think that's all good and fine, but why is Hollgi telling me all this? Because it's important to know how big the declination is and to compensate for it. Depending on where in the world you are, the difference between true and magnetic north can be somewhere from 0 degrees (perfect) to over 90 degrees (extreme), which would makes any navigation without compensation absolutely useless.

So how do we know how big the declination is? Normally you find a little diagram on your chart which tells you: {mosimage} -the magnetic north -the true north -and the grind north - with the corresponding angles To give you a rough idea of how much variance there is around the coast of Australia:
Sydney: 13°E Canberra: 12.5°E Brisbane: 11.5°E Darwin: 3.5°E Broome: 3°E Perth: 2°W Adelaide: 8.5°E Hobart: 15°E

Your GPS wants to know as well which north to use. Tell it: - magnetic north if you use it together with a non compensated compass, - true north with a compensated one - true north if you use a lat /long map - grid north if you use a UTM map/ chart So now you see, there´s north, north and north! But after all it's not that difficult. Correct your compass or allow for the declination and you´ll arrive where you want to go.