DougPaul
Well-known member
It would work, except that I don't bring a chart table and parallel ruler with me when hiking...KayakDan said:
(They do work nicely when sailing, however.
)Doug
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true north compass deviation?
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(They do work nicely when sailing, however.
)Doug
Mac
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Magnetic North
Interestingly, the magnetic pole located in the Northern Hemisphere is soon leaving (or has already left) northern Canada heading for Siberia.
Interestingly, the magnetic pole located in the Northern Hemisphere is soon leaving (or has already left) northern Canada heading for Siberia.
>>On a somewhat related tack,why don't land maps use a "compass rose" as used on nautical charts? <<
What Doug said (chart tables).
In some ways, one DOES use the meridian lines printed on land maps in more-or-less the same way as one uses the "compass rose" on the nautical chart.
That is... one aligns the compass capsule with the meridian lines and then aligns the compass base with direction of travel. Take the bearing from the compass and then add (or subtract if you're out west) declination to get magnetic course.
That's a similar process to using a compass rose - particularly if one is charting with one of those wheel-doo-hickies with the ruler attached (forget what they're called), rather than the divider type thing-a-ma-bobs (don't remember what THEY'RE called, either).
Gotta say... there ain't NOTHING as cool as a good set of nautical charts. Those things are wonderful.
What Doug said (chart tables).
In some ways, one DOES use the meridian lines printed on land maps in more-or-less the same way as one uses the "compass rose" on the nautical chart.
That is... one aligns the compass capsule with the meridian lines and then aligns the compass base with direction of travel. Take the bearing from the compass and then add (or subtract if you're out west) declination to get magnetic course.
That's a similar process to using a compass rose - particularly if one is charting with one of those wheel-doo-hickies with the ruler attached (forget what they're called), rather than the divider type thing-a-ma-bobs (don't remember what THEY'RE called, either).
Gotta say... there ain't NOTHING as cool as a good set of nautical charts. Those things are wonderful.
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dougb
New member
KayakDan said:
I think it's because the maps were developed to be used differently. Nautical maps are (historically?) used by rolling them out on a chart table. Land maps are more likely to be folded up, and are usually smaller to start with. The detail on the land map would get covered up by a large compass rose. With a land map, you can orient the map to north by setting a compass on it, where it's time consuming to spin the ship around so you can get your lubber line parallel with to map.
DougPaul
Well-known member
The whole process is even easier if you have a protracter compass with automatic declination.linehant said:
Map to world:
Just line up the compass edge along the bearing of interest on the map and rotate the compass dial until the N-S lines are parallel to a N-S line on the map. Then sight away.
World to map:
Take your sight (rotate the compass dial into the correct position). Now rotate the compass as a unit until the N-S lines are parallel to the N-S lines on the map and slide the compass around until the edge touches the reference location.
No numbers, no arithemetic, and no compass roses. You do, however, have to set the correct declination on the compass.
Doug
sardog1
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Well, I hate to do this, 'cuz it will reduce the working opportunities for my dog.
If you cannot remember (or decipher) any of the various mnemonics, and you don't have (or cannot decipher) an "automatic" declination adjustment on your compass, there's an easy way to avoid the whole issue. Any map that's useful for foot navigation should have a diagram of an angle representing the magnetic declination from true north.
Use that diagram and a long straightedge (e.g., a foot long ruler) to draw parallel lines that point to magnetic north. Now you can use those lines to orient your mapping compass (aka an orienteering compass, aka a "Silva-type" compass.) This is what's done on orienteering maps, as described above, to facilitate quick navigation and avoid errors under the stress of "cunning running." (Be sure you're using the angle between magnetic north and true north, not grid north and true north.)
If you're still using a lensatic compass, put it on the shelf where it can be stored safely until it's passed down to your heirs as an antique. Go out and buy the other type described above. Don't worry, your boot camp instructor will never know the difference.
If you're still using just a ball-type compass, your heirs might be getting your compass pretty quick. Or at least carry some dog treats for when we find you.
If you don't carry and use a compass at all, put the dog treats in an accessible outside pocket, along with your final wishes.
If you cannot remember (or decipher) any of the various mnemonics, and you don't have (or cannot decipher) an "automatic" declination adjustment on your compass, there's an easy way to avoid the whole issue. Any map that's useful for foot navigation should have a diagram of an angle representing the magnetic declination from true north.
Use that diagram and a long straightedge (e.g., a foot long ruler) to draw parallel lines that point to magnetic north. Now you can use those lines to orient your mapping compass (aka an orienteering compass, aka a "Silva-type" compass.) This is what's done on orienteering maps, as described above, to facilitate quick navigation and avoid errors under the stress of "cunning running." (Be sure you're using the angle between magnetic north and true north, not grid north and true north.)
If you're still using a lensatic compass, put it on the shelf where it can be stored safely until it's passed down to your heirs as an antique. Go out and buy the other type described above. Don't worry, your boot camp instructor will never know the difference.
If you're still using just a ball-type compass, your heirs might be getting your compass pretty quick. Or at least carry some dog treats for when we find you.
If you don't carry and use a compass at all, put the dog treats in an accessible outside pocket, along with your final wishes.
DougPaul
Well-known member
Can I leave a trail of dog treats behind me?sardog1 said:If you don't carry and use a compass at all, put the dog treats in an accessible outside pocket, along with your final wishes.
Doug
Nessmuk
Active member
This is the method I have used and taught for years. Foolproof and simple, fast to use in the field. It has the advantage of allowing you to do a little map study while you are drawing the lines. If your compass is so equipped, make sure the declination correction adjustment is set to zero for this method.sardog1 said:
One cautionary note... do not simply extend the MN line from the little diagram in the legend. USGS will tell you that the angle represented there in the diagram is just an approximation of the actual declination, plus trying to extend an inch long line across the entire map just wouldn't be very accurate.
Get yourself a cheap grade school type protractor, the semicircle kind with a 6 inch straightedge, and place it on the edge of the map at the correct angle (your compass can also provide this function if you think about it). You now have a 6 inch straightedge at the correct angle that you can better extend across the map. Now you can use a longer straightedge like a yardstick laid against the protractor to transfer the parallel lines.
When you are finished you should have a series of parallel MN pointing lines, spaced an inch or two apart across the region you expect to be traveling. In trying to figure out how to use the protractor and draw lines, you only have to keep in mind that you are simply recreating the exact angle represented in the MN/TN legend picture by drawing the angled lines on the map. Look at the diagram and you won't screw up with a grossly wrong +/- angle. In regions of the USA to the east of Chicago the lines slant NW/SE, to the west of Chicago they slant NE/SW. No math involved.
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uberturtle
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Now, here's the quiz, is there a sailor out there who'll tell us the opposite memory aid for True, Variation, Magnetic, Deviation, Compass?[/QUOTE]
True Virgins Make Dull Companions After Weddings
True Variation Magnetic Deviation Compass (Add West)
Funny, I've always remembered this one better.......
True Virgins Make Dull Companions After Weddings
True Variation Magnetic Deviation Compass (Add West)
Funny, I've always remembered this one better.......
NYBRAD
New member
Us jar heads used this to keep it stupid simple......
"LARS"
Left add, Right Subtract......
"LARS"
Left add, Right Subtract......
DougPaul
Well-known member
NYBRAD said:
Which direction? (Looks like map-to-compass to me.)
Doug
