TACTICAL MAP NOW FOR SALE

[Shaman]

Just a quick question from a lurker:

Normally when the magnetic declination (or better: variation) is negative,

you have to ADD it to the course you obtain from the chart. This because the convention is that Westerly variation/declination is negative in calculations...

Any thoughts on why thisworks the other way around on this map?

 

Pilots have an easy say for calculating magnetic heading from true (map) headings:

 

WEST BEST (you add to true heading from map) - by WEST i mean WEST DECLINATION

EAST LEAST (you subtract from true heading)

 

In case of Georgia EAST declination. 6 deg EAST (6E) or (+6).

TH-MD=MH

 

WEST BEST -> TH-(-MD)=TH+|MD| see? you add it (BEST) ... so in case of 10deg W of magnetic declination and true heading of 100, magnetic heading to follow is 110

EAST LEAST -> TH-(+MD)=TH-|MD| you substract it (LEAST)....so in case of 10deg E ...... true heading of 100, magnetic heading is 90.

Edited March 1, 2011 by Shaman

[igormk]

Just a quick question from a lurker:

Normally when the magnetic declination (or better: variation) is negative,

you have to ADD it to the course you obtain from the chart. This because the convention is that Westerly variation/declination is negative in calculations...

Any thoughts on why thisworks the other way around on this map?

mterlaak, if you are talking about the explanation of how to correct the declination (or variation if you like) with general correction of -5 degrees it is actually the direct value which user should use to get the magnetic course.

 

Otherwise, you are right - it should be 5 degrees East, meaning that you should subtract 5 degrees from the course measured from the map in order to get the required magnetic heading.

 

So once again - mentioned -5 degrees is direct correction to be applied.

 

S!

[JimMack]

In the Navy we were taught this mnemonic - CADET

From Compass, AD East to get a True bearing.

 

As long as you remember CADET, you will never have a problem again of wondering whether to add or subtract!

[mtuckner]

On the declination diagram use the mnemonic LARS. Left Add, Right Subtract. If you are moving form grid to magnetic, see which way you move in the declination diagram, from left to right or the opposite. Then use LARS to see if you add or subtract the amount to get what you need. Same works from magnetic to grid azimuth.

[Shaman]

In the Navy we were taught this mnemonic - CADET

From Compass, AD East to get a True bearing.

 

As long as you remember CADET, you will never have a problem again of wondering whether to add or subtract!

 

This is totally new for me :) I have learned "WEST BEST, EAST LEAST" during my PPL training, works since then great for me. Headaches gone :)

[effte]

In aviation, you're always going map to compass, hence "west best". Perhaps the navy has it the other way to facilitate plotting and ded reckoning, going from compass to chart?

 

As for putting a sign on the variation instead of stating whether it is easterly or westerly, that is opening a can of worms. I challenge you to find an authoritative source on what sign to put on an easterly variation. I tried, and found nothing but I think I eventually found two authoritative sources. Of course they didn't agree.

[NRG-Vampire]

moderators, please ban these advert members for a life

 

 

and i suggest if they do a forum registration, please delay the registrations for 24 hours (for everybody)

hopefully it will decreasing spam numbers

 

********************************

edit: plenty advertising "replies" were here and in many other threads but fortunately moderators deleted these spams quickly

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Edited September 7, 2013 by NRG-Vampire

[igormk]

Post edited by user because of... because of...

 

hmm... hmm... hmm...

 

...because of bad Situational Awareness of the same user.

 

:P

Edited September 8, 2013 by igormk

[igormk]

The forums are beeing spammed, the posts he was reffering to has been deleted now.

 

Ah! OK, I wasn' aware of that. :P I was thinking it was directed towards the first post... So I apologize, and if possible delete my reply than. Thank you!

[Flagrum]

Ah! OK, I wasn' aware of that. :P I was thinking it was directed towards the first post... So I apologize, and if possible delete my reply than. Thank you!

:doh::smilewink:

 

But you can always edit your own postings.

[Emmer]

:doh::smilewink:

 

But you can always edit your own postings.

 

Yep...........:thumbup:

[Ramjet]

There is a good plugin for vbulletin that can trim down the number of spammers getting through quite significantly. It is a simple plugin as well. It just requires a minimum amount of time during registration. (for example, 15 seconds is a pretty good minimum setting, as real people won't register that quickly) Basically, if anyone registers in less time than the minimum set time, their registration is automatically denied.

 

The bot type of spammers tend to register in under 2 seconds, so you can thin out upwards of 80% of the spammers making it through the registration process.

[Raven68]

Moderators can you close this thread please?

[=Mac=]

The American Practical Navigator (colloquially often referred to as Bowditch), originally written by Nathaniel Bowditch

Quoting: (emphasis mine)

 

625. Variation And Deviation

 

Variation is the angle between the magnetic meridian and the true meridian at a given location. If the northerly part of the magnetic meridian lies to the right of the true meridian, the variation is easterly. Conversely, if this part is to the left of the true meridian, the variation is westerly. The local variation and its small annual change are noted on the compass rose of all navigational charts. Thus the true and magnetic headings of a ship differ by the local variation.

 

As previously explained, a ship’s magnetic influence will generally cause the compass needle to deflect from the magnetic meridian. This angle of deflection is called deviation. If the north end of the needle points east of the magnetic meridian, the deviation is easterly; if it points west of the magnetic meridian, the deviation is westerly.

 

626. Heading Relationships

 

A summary of heading relationships follows:

 

1. Deviation is the difference between the compass heading and the magnetic heading.

2. Variation is the difference between the magnetic heading and the true heading.

3. The algebraic sum of deviation and variation is the compass error.

 

The following simple rules will assist in correcting and uncorrecting the compass:

 

1. Compass least, error east; compass best, error west.

2. When correcting, add easterly errors, subtract westerly errors (Remember: “Correcting Add East”).

3. When uncorrecting, subtract easterly errors, add westerly errors.

 

Some typical correction operations follow:

 

Compass Deviation Magnetic Variation True

-> +E, -W

358 5 E 003 6 E 009

120 1 W 119 3 E 122

180 6 E 186 8 W 178

240 5 W 235 7 W 228

+W, -E <-

 

I'm not sure that table will come out right in this forum.

 

Use the memory aid “Can Dead Men Vote Twice, At Elections” to remember the conversion process (Compass, Deviation, Magnetic, Variation, True; Add East). When converting compass heading to true heading, add easterly deviations and variations and subtract westerly deviations and variations.

The same rules apply to correcting gyrocompass errors, although gyro errors always apply in the same direction. That is, they are E or W all around the compass.

Complete familiarity with the correcting of compasses is essential for navigation by magnetic or gyro compass. The professional navigator who deals with them continually can do them in his head quickly and accurately.

[Sharpe_95]

Mods please can we lock/move/delete this thread? Even IF it was an official update/news it no longer is.

Please remove/lock/delete.

-Sharpe