Navagation

[charlieharper]

Hi all, just a quick question. Whilst in the Armed Forces I was taught to navigate by using the "Mag to grid get rid/ Grid to mag add" is this the same as this eastings and westings thing I keep reading about?

Thanks Charlie

 

[Mrnotming]

Hi Charlie,
Sounds like it is an adjustment for magnetic variation? So the marine chart will have this marked on the compass rose.Depending on where you are in the world, the correction could be plus or minus.Changes annually usually by a small amount.
Here is a link:
http://msi.nga.mil/NGAPortal/MSI.portal?_nfpb=true&_pageLabel=msi_portal_page_69&prodCode=02

 

[PuffTheMagicDragon]

"East is least, West is best"?

 

[Baddox]

Swapping between mag, true and compass bearings needs to adjusted for declination and deviation. So to answer your question, the difference between each reading could be either east or west. Then the rhyme “error west compass best (meaning biggest value)” and “error east compass least” works.

"Mag to grid get rid/ Grid to mag add" will only apply when magnetic north is west of true/grid north.

 

[lpdsn]

That mnemonic might be referring to the OS grid.

Anyway, you'll need to do something similar to convert between magnetic and true. The one I use, similar to PuffTheMagicDragon is if the Variation is West, Compass is best (i.e. add the Variation to True to get Magnetic) and if variation is East, Compass is least (i.e. subtract to get Magnetic)

 

[JumbleDuck]

"East is least, West is best"?

"Magnetic is ten more than true, near enough, and who knows or cares what the deviation is?"

 

[johnalison]

"Magnetic is ten more than true, near enough, and who knows or cares what the deviation is?"

I did when I mounted a fire extinguisher bracket next to the compass and got 14 degrees deviation for my sins.

I can't remember mnemonics; I just keep a mental picture of the compass grid in my mind.

 

[PuffTheMagicDragon]

"Magnetic is ten more than true, near enough, and who knows or cares what the deviation is?"

...especially since most people I know rely on their GPS.

 

[KAL]

Hi all, just a quick question. Whilst in the Armed Forces I was taught to navigate by using the "Mag to grid get rid/ Grid to mag add" is this the same as this eastings and westings thing I keep reading about?

Thanks Charlie

When I first learned to navigate a yacht, all my previous navigation experience was as a mountain leader and in mountain rescue, where we commonly used "Add for mag, get rid for grid" to convert between magnetic and true bearings, so that is what I used. It still works, although Baddox is right about W variation.

If the vast majority of your sailing is in local waters, then you should be fine as you are, otherwise swap to the west is best thing...

 

[capnsensible]

"Magnetic is ten more than true, near enough, and who knows or cares what the deviation is?"

Is this a troll? :nonchalance:

 

[JumbleDuck]

Is this a troll? :nonchalance:

Brutal realism.

 

[LadyInBed]

I was taught grid to mag add in the army, but the may variation has changed (decreased) a lot since then to the point at which they are the same or gone to the 'other side' of zero making the addage untrue.
See. https://www.ordnancesurvey.co.uk/resources/maps-and-geographic-resources/finding-north.html

 

[Daydream believer]

"Magnetic is ten more than true, near enough, and who knows or cares what the deviation is?"

Magnetic variation for Scotland ( discounting any exceptional local variation) varies between 2. ( around Peterhead)& 5 degrees( far west isles) to the nearest degree
So your 10 ( assuming you mean degrees) is somewhat out.
Unless you are referring to the swing to the Scottish communist party - Sorry I meant SNP

 

[awol]

"Magnetic is ten more than true, near enough, and who knows or cares what the deviation is?"

At 11'E per year that makes your charts about 27 years old. Maybe not too old in paleogeological terms but they've invented cardinal marks since then and all the black starboard hand buoys have gone.

 

[JumbleDuck]

Magnetic variation for Scotland ( discounting any exceptional local variation) varies between 2. ( around Peterhead)& 5 degrees( far west isles) to the nearest degree
So your 10 ( assuming you mean degrees) is somewhat out.
Unless you are referring to the swing to the Scottish communist party - Sorry I meant SNP

At 11'E per year that makes your charts about 27 years old. Maybe not too old in paleogeological terms but they've invented cardinal marks since then and all the black starboard hand buoys have gone.

They are indeed 27 years old. "Between five and two" is close enough to "zero" for me ... my life just got (even) easier!

 

[Daydream believer]

They are indeed 27 years old. "Between five and two" is close enough to "zero" for me ... my life just got (even) easier!

Yes, I suppose if you spend your life motoring up & down the Calledonian Canal then you should be OK
especially if you stay on Loch Oich & do not attempt any of those nasty Lock thingies

 

[JumbleDuck]

Yes, I suppose if you spend your life motoring up & down the Calledonian Canal then you should be OK
especially if you stay on Loch Oich & do not attempt any of those nasty Lock thingies

Who needs accurate compass work to get into a lock? It's much easier just to look.