Compass declination

[daintreeboy]

hi

This is my first post here, new to bushwalking basically just walked flagged trails up until now looking to go a bit more off road. I just ordered a compass off the cuff without too much thought and bought the suunto a30 compass. After doing a bit more reading about magnetic variation I'm not sure if I should have went with the next model up so I can adjust this out. I found a website that said you can just mark your variation with a marker pen (6 degrees east where I live) and just roll with it.

I'm kinda confused though my walking is in the nth qld rainforest and mountains here where you cant see more than 20 metres climbing steep ridgelines. My reason for the compass was to just have a general direction of where I'm headed when going up said ridgelines with no visibility due to rainforest. With the model Ive ordered will that mean it will be 6 degrees off every time I look at it whilst going up hills because I cant adjust the declination out of it? I'm not talking about taking a bearing and the adding of subtracting compass error to follow a bearing I realise you can manually adjust the error out when doing that. My question is more in relation to just looking down at the compass whilst not following a bearing and going ok I'm heading 182 south will that always be 6 degrees out with the A30 whilst doing that?

I hope that's not too confusing.

thanks

[neilmny]

Hi daintreeboy and welcome to the forum.
This article might help http://www.ronwatters.com/Declination.html
Simply put declination is needed to relate a compass bearing back to a paper map.
Your 182 degrees bearing will only be out in relation to a map. If I understand what you mean.......you take a bearing on something then follow that bearing.
You can do this but you can't relate it directly to a map.
There is some good navigation stuff here too https://mbw.org.au/mbw_activities/train ... gation.php

[slparker]

The compass needle always points to magnetic north. The '6 degrees' difference is variation betwwen between the magnetic bearing of the compass and the grid lines on the map, which are 6 degrees apart (depending on where you are on the earth's surface - it could be 10 degrees for example in some areas).

You just need to set the bearing on your compass to account for this difference. To convert a grid to magnetic bearing you subtract the magnetic variation, the magnetic variation is found in the legend in the bottom of the map. It does move every couple of years so you have to add in the yearly variation. I prsume this is what you mean by '6 degrees'

For example if you plot a bearing on your map which is 140 degrees from grid north when you convert it to a compass bearing you have to subtract the magnetic variation which, if it 6 degrees, leads to a compass bearing of 134 degrees.

If you then follow this compass bearing it will lead you to the point on the ground that corresponds with the point on the map.

You still have to follow this procedure with a compass with 'declination' you can just set it permanently, I believe, so that it is always preset with the magnetic variation (declination) in your area. i have never used a compass with declination and it just means some extra maths every time you plot a bearing. You don't need a new compass and compasses with declination are not inherently more accurate.

I reckon that navigating with a compass in close country in Qld is *&%$#! hard. I lived there for a couple of years back when a gps was uncommon (i never had one). If you are unfamiliar with navigation a gps and some navigation lessons at your local club is never a bad idea.

[wildwanderer]

My question is more in relation to just looking down at the compass whilst not following a bearing and going ok I'm heading 182 south will that always be 6 degrees out with the A30 whilst doing that?
thanks

At your location in North Queensland the magnetic bearing (compass bearing) will be minus 6 degrees off the grid bearing. (the bearing you get when you plan a direction on a map).

If your only needing to get your general sense of direction, then those 6 degree wont matter.

Example you walk down a hill and see two possible spurs heading further down. One heading South and the other descending to the East. You know you need to head down the south spur. (as when planning your route on the map it told you the spurs direction was at 182 grid bearing)

You look at your compass and it says 182. Even counting the 6 degree variation (188) its still south, so it will be clear which spur you need to use.

If your need to do more precise navigation just get used to adding 6 degrees in your head when you look at your compass.

As slparker noted the variation changes depending on location.

[daintreeboy]

Thanks everyone that makes it clearer I think I will just roll with the suunto A30.

Most of my walks here you don't get a view of anything except dense rainforest until you get to the summit. I mostly just want a compass to know I'm roughly heading southwest at the moment on this ridge etc. in the jungle up here everything looks the same.

We average over 4metres of rainfall around here on the coast with the mountain peaks getting more than 10 metres a year in some cases. The wait a while vine is an absolutely nightmare on all rarely used trails.

[wildwanderer]

Thanks everyone that makes it clearer I think I will just roll with the suunto A30.

Most of my walks here you don't get a view of anything except dense rainforest until you get to the summit. I mostly just want a compass to know I'm roughly heading southwest at the moment on this ridge etc. in the jungle up here everything looks the same.

We average over 4metres of rainfall around here on the coast with the mountain peaks getting more than 10 metres a year in some cases. The wait a while vine is an absolutely nightmare on all rarely used trails.

Its very tough in dense foliage especially if the terrain is also flat and there are no obvious terrain features like stream beds etc. If you need to follow a compass bearing and there are many obstacles you need to go around.. a common technique is to pick a distinctive tree or object in a direct line of sight along the compass bearing. Then put your compass away and make your way to that tree. Then find another tree/object 20 metres away along the compass bearing.

Slow but it works. Just dont forget which tree!

[neilmny]

Just one question daintreeboy, is the compass you bought for the southern hemisphere? I believe it should be an A30 SH.
This matters as if it is a northern hemisphere compass (NH suffix) the needle will dip down and drag at the point which is a PITA.

[Rileyr]

Navigating in dense undergrowth can be tough. If you are heading to major features then any decent compass (southern hemisphere as stated by others) should be fine.

If you need to be accurate with bearings then a prismatic compass might be an idea. You can look through it and be given the exact bearing rather then looking down at the compass and following the needle up to a target destination. Prismatics arent cheap though.

As others have said, its best to pick a point on your bearing and walk toward it and repeat.

Another option is to get a cheap gps for backup. I think all of them these days will give you your current location, be able to track where you have gone and guide you to a location. A good way to check your nav. Esspecially if your by yourself!

Sent from my SM-G950F using Tapatalk

[daintreeboy]

Just one question daintreeboy, is the compass you bought for the southern hemisphere? I believe it should be an A30 SH.
This matters as if it is a northern hemisphere compass (NH suffix) the needle will dip down and drag at the point which is a PITA.

Hi I'm not sure to be honest I haven't received it yet I bought it from the wild earth shop which is Australian. If it's the wrong one I will send it back thanks for pointing that out

[neilmny]

If it is this one no probs https://www.wildearth.com.au/buy/suunto ... *&%$#!/209501?
Balanced for southern hemnisphere in the features.

[Camminata]

My question is more in relation to just looking down at the compass whilst not following a bearing and going ok I'm heading 182 south will that always be 6 degrees out with the A30 whilst doing that?
thanks

At your location in North Queensland the magnetic bearing (compass bearing) will be minus 6 degrees off the grid bearing. (the bearing you get when you plan a direction on a map).

If your only needing to get your general sense of direction, then those 6 degree wont matter.

Example you walk down a hill and see two possible spurs heading further down. One heading South and the other descending to the East. You know you need to head down the south spur. (as when planning your route on the map it told you the spurs direction was at 182 grid bearing)

You look at your compass and it says 182. Even counting the 6 degree variation (188) its still south, so it will be clear which spur you need to use.

If your need to do more precise navigation just get used to adding 6 degrees in your head when you look at your compass.


As slparker noted the variation changes depending on location.

Nth Queensland declination is positive East + meaning you adding 6 from your bearing GridNorth. Minus 6 would be negative west - subtracting the 6.
Can only be positive ADDING THE 6. correct me if im wrong?? have always wondered about declination but never used it in the field as I don't think its necessary in a short distance

[rcaffin]

The Suunto A30 is perfectly adequate for just about any travel in Oz, at any skill level. The big ring lets you adjust it for declination.
Won't work in the Antarctic or the Arctic, but that is another matter.

Cheers
Roger

[ChrisJHC]

My question is more in relation to just looking down at the compass whilst not following a bearing and going ok I'm heading 182 south will that always be 6 degrees out with the A30 whilst doing that?
thanks

At your location in North Queensland the magnetic bearing (compass bearing) will be minus 6 degrees off the grid bearing. (the bearing you get when you plan a direction on a map).

If your only needing to get your general sense of direction, then those 6 degree wont matter.

Example you walk down a hill and see two possible spurs heading further down. One heading South and the other descending to the East. You know you need to head down the south spur. (as when planning your route on the map it told you the spurs direction was at 182 grid bearing)

You look at your compass and it says 182. Even counting the 6 degree variation (188) its still south, so it will be clear which spur you need to use.

If your need to do more precise navigation just get used to adding 6 degrees in your head when you look at your compass.


As slparker noted the variation changes depending on location.

Nth Queensland declination is positive East + meaning you adding 6 from your bearing GridNorth. Minus 6 would be negative west - subtracting the 6.
Can only be positive ADDING THE 6. correct me if im wrong?? have always wondered about declination but never used it in the field as I don't think its necessary in a short distance

In the old days we used to teach “Grid to Magnetic, Subtract. Magnetic to Grid, Add”.

Helped by the mnemonic “Grand Ma Sucks” or the MG-A car (like the MG-B).

Both of these refer to a +ve or easterly declination.

E.g. In Melbourne at the moment the declination is around 12 degrees Easterly (Positive). If you plot a grid bearing on the map of 194 degrees (referencing Grid North), you would subtract the declination of +12 to get a magnetic bearing of 182 degrees.

[Camminata]

As slparker noted the variation changes depending on location.[/quote]

Nth Queensland declination is positive East + meaning you adding 6 from your bearing GridNorth. Minus 6 would be negative west - subtracting the 6.
Can only be positive ADDING THE 6. correct me if im wrong?? have always wondered about declination but never used it in the field as I don't think its necessary in a short distance[/quote]In the old days we used to teach “Grid to Magnetic, Subtract. Magnetic to Grid, Add”.

Helped by the mnemonic “Grand Ma Sucks” or the MG-A car (like the MG-B).

Both of these refer to a +ve or easterly declination.

E.g. In Melbourne at the moment the declination is around 12 degrees Easterly (Positive). If you plot a grid bearing on the map of 194 degrees (referencing Grid North), you would subtract the declination of +12 to get a magnetic bearing of 182 degrees.[/quote]


so for example if I shoot bearing magnetic facing a NW direction you would add the 12?

[ChrisJHC]

As slparker noted the variation changes depending on location.

Nth Queensland declination is positive East + meaning you adding 6 from your bearing GridNorth. Minus 6 would be negative west - subtracting the 6.
Can only be positive ADDING THE 6. correct me if im wrong?? have always wondered about declination but never used it in the field as I don't think its necessary in a short distance[/quote]In the old days we used to teach “Grid to Magnetic, Subtract. Magnetic to Grid, Add”.

Helped by the mnemonic “Grand Ma Sucks” or the MG-A car (like the MG-B).

Both of these refer to a +ve or easterly declination.

E.g. In Melbourne at the moment the declination is around 12 degrees Easterly (Positive). If you plot a grid bearing on the map of 194 degrees (referencing Grid North), you would subtract the declination of +12 to get a magnetic bearing of 182 degrees.[/quote]


so for example if I shoot bearing magnetic facing a NW direction you would add the 12?[/quote]

It doesn’t matter which way you’re facing!
With an easterly (+ve) declination, you always add the 12 to convert from magnetic to grid.

[slparker]

ChrisJC is correct.

The purpose of converting the bearing from grid-magnetic is not because of the direction you are facing, it is because the reference lines on the map (the grid) point to a different place on the earth's surface than th ereference lines on the compass (the bearing taken as an angle from magnetic north). That is; grid north and magnetic north are two different points on the earth's surface: the map points to grid north and the compass points to magnetic north.

If you look at the legend on the map you will see that there is a three pronged symbol with true north (where the axis of the earth's spin meets the surface of the planet: the north pole) as the fixed point of reference. this point does not move, it is the axis of the earth's spin and is a real, fixed physical location.

Magnetic north is a real physical location but it is not fixed, it migrates every year and, at the moment, is close to true north but it isn't quite in the same direction.

Grid North is imaginary, it is not a physical location on the earth's surface but is the point where the projection of the map meets at the top of the globe. -This projection is an approximation because a square map does not fit neatly on the curved surface of the planet. Grid north is close to, but not quite at the same location as true north and magnetic north.

So, to shoot an accurate bearing you should convert grid-magnetic. the added problem is that the magnetic north moves every year and you also should convert that using the guide in the legend, to be most accurate.

Just to reiterate, the physical paper map is an approximation of the earth's surface (think of the large scale weird projection of the world map: with a massive greenland - a 1:50 000 map is a less distorted version of this) .

It is approximate because a square map doesn't fit neatly onto a spherical surface. If it was an exact match the grid lines would meet at the north pole(True North) but even in this ideal circumatance you would still have to convert grid-magnetic because magnetic north is just handily situated near, but not at, true north.

I could explain it really easily with a globe in my hand and a piece of paper and pen but it's difficult to put into easily understood words - I should create a short youtube clip...

[peregrinator]

I reckon you have explained it beautifully.

[ChrisJHC]

As a matter of interest, at the moment there is a location in the UK where True, Grid and Magnetic North all align.

It does move each day as the magnetic field of the earth varies.