Ellen's COG

[doris]

Ellen\'s COG

Can some please explain to me the difference between Ellen's heading and COG. I can't believe that B&Q makes that much leeway. At her speeds there cannot be much current effecting her. Getting difficult to type with ones fingers crossed all the time but it is starting to look as if she has a v. serious chance. Brilliant girl!!

 

[tangaroa]

Re: Ellen\'s COG

Magnetic variation at 2 degrees north, 30 degrees west is more than 18 degrees west. Hence difference between magnetic heading and COG /forums/images/graemlins/smile.gif

 

[doris]

Re: Ellen\'s COG

Ta v. much. What charts do just happen to have lying around??

 

[BlueSkyNick]

Re: Ellen\'s COG

Blimey, I have learned something new today - didn't realise it was that much.

So where is the largest variation on the planet, then?

 

[FWB]

Re: Ellen\'s COG

See here for Mag Variation

http://www.pangolin.co.nz/almanac/magvar.php

 

[Goodge]

Re: Ellen\'s COG

That's amazing.. by moving the cursor around I found a spot in the Southern Atlantic with variation of 25.52 deg W !

You wouldn't want to ignore that in your calculations would you !

 

[Rowana]

Re: Ellen\'s COG

Try going right down to the bottom between Oz and Africa ! !

 

[FWB]

Re: Ellen\'s COG

I always use true...cant see the point of using a standard compass except when the electrics fail. I imagine Ellen must use true also. Why use mag at all if you've got a readout in true?

 

[iangrant]

Re: Ellen\'s COG

I looked the other day - struck me that it will make quite a difference - not really bothered with it recently with the couple of degrees on the S coast. Hence the course to steer question!

 

[geoffatstanpit]

Re: Ellen\'s COG

Must be 180 deg, just north of magnetic north pole! Can't get much more than that.

Geoff

 

[Woodentop]

Re: Ellen\'s COG

If you get into the far north of Canada it will be 180 degrees.

Not sure exactly where - it keeps moving.

 

[AlexL]

Re: Ellen\'s COG

Its also a matter of terminology. In the absence of any other information "Heading" is always assumed to be magnetic whilst "Course" is assumed to be True. Obviously one could clarify it differently by saying "A heading of 270(T)" but the above useally applies as standard.

 

[ShipsWoofy]

Re: Ellen\'s COG

this can't be correct Shirley!

Since this is not a magnetic compass, or at least it appears to be a direct read from B&Q's electronic instruments.

 

[machurley22]

Re: Ellen\'s COG

Don't understand your point Woofy. Are you saying that this can't be a magnetic heading (despite the fact that it is labelled as such) since it is electronic?

Dave

 

[ShipsWoofy]

Re: Ellen\'s COG

I presumed, electronic compasses although using the Earths magnetic field would compensate for any errors. From your response, I guess this was a bad presumption.

Does this mean you still need a deviation card with a fluxgate?

 

[BrendanS]

Re: Ellen\'s COG

It depends which model you have really.

Fluxgate compasses are affected by deviation and variation, just like a normal magnetic compass. Most will autocalibrate for deviation, by putting into a calibration mode and sailing in circles.

More advanced models will correct for variation if connected to a suitable gps or plotter