Variation and deviation +/- convention

[VicS]

>I have never heard of variation referred to as + or -, only ever east or west as shown on charts.

What prompted this question was this posted on another thread. Variation and deviation both being given as +3

 

[Birdseye]

I have never heard of variation referred to as + or -, only ever east or west as shown on charts. Whether you + or - east or west depends what you are trying to do - go from compass to true or true to compass.

No it doesnt. The variation is simply the difference between true north and magnetic north. True north is always in the same direction but the earths magnetic field wanders about a bit. So the direction of the magnetic north is given by a "variation" on the true north. If you have 5 deg of westerly variation that means that the magnetic north is off to the west of true north and so your compass course is your true course plus 5.

Rather than get tangled up in mnemonics, its much easier to visualise a globe with the magnetic pole off to one direction from the true pole. That way you can work with either + / - ,or east / west . Its noddy maths really.

By thge way does anyone ever use magnetic bearings outside RYA exams, now that we have GPS and can navigate complete;ly in T ? I can honestly say I have never used the compass on my boat and I have had that boat for 6 years.

 

[laika]

By thge way does anyone ever use magnetic bearings outside RYA exams, now that we have GPS and can navigate complete;ly in T ? I can honestly say I have never used the compass on my boat and I have had that boat for 6 years.

yes

[edit]. Sorry. To clarify. (1) I'd rather use a compass than GPS for fine grained pilotage. (2) The art of navigation is a fundamental part of my enjoyment of sailing.

 

[alanch]

No it doesnt. The variation is simply the difference between true north and magnetic north. True north is always in the same direction but the earths magnetic field wanders about a bit. So the direction of the magnetic north is given by a "variation" on the true north. If you have 5 deg of westerly variation that means that the magnetic north is off to the west of true north and so your compass course is your true course plus 5.

Yes it does. Going from compass to true add east minus west, from true to compass add west minus east. Applying variation to your true course gives magnetic course, then applying deviation gives you compass course.

 

[AngusMcDoon]

What prompted this question was this posted on another thread. Variation and deviation both being given as +3

To have the measured value (heading from the compass) and its error (variation) using the same sense (positive clockwise) makes, er, sense. If one went one way and the other went the other it would make my little bear-like brain throb.

 

[lw395]

>I have never heard of variation referred to as + or -, only ever east or west as shown on charts.

Agree.

In aviation it is normally + or - apparently.

I must admit I use the 'variation east, compass least' aide memoir.

Along with 'it's less than 5 degrees, forgeddabouddit'.

 

[johnalison]

It will be interesting when magnetic north flips to the South Pole. Especially since all radio and satellite communications will be zapped by the sun's rays while the magnetic field re establishes itself.

 

[AngusMcDoon]

It will be interesting when magnetic north flips to the South Pole.

As the magnetic north pole is actually a magnetic south pole then when it flips it will all line up perficly.