SailNet Community - Reply to Topic

   Search Sailnet:

 forums  store  


Quick Menu
Forums           
Articles          
Galleries        
Boat Reviews  
Classifieds     
Search SailNet 
Boat Search (new)

Shop the
SailNet Store
Anchor Locker
Boatbuilding & Repair
Charts
Clothing
Electrical
Electronics
Engine
Hatches and Portlights
Interior And Galley
Maintenance
Marine Electronics
Navigation
Other Items
Plumbing and Pumps
Rigging
Safety
Sailing Hardware
Trailer & Watersports
Clearance Items

Advertise Here






Go Back   SailNet Community > On Board > Gear & Maintenance > N hemispere binoc w compass not working in S?
 Not a Member? 


Thread: N hemispere binoc w compass not working in S? Reply to Thread
Title:
  

By choosing to post the reply below you agree to the rules you agreed to when joining Sailnet.
Click Here to view those rules.

Message:
Trackback:
Send Trackbacks to (Separate multiple URLs with spaces) :
Post Icons
You may choose an icon for your message from the following list:
 

Register Now

In order to be able to post messages on the SailNet Community forums, you must first register.
Please enter your desired user name, your email address and other required details in the form below.
Please note: After entering 3 characters a list of Usernames already in use will appear and the list will disappear once a valid Username is entered.
User Name:
Password
Please enter a password for your user account. Note that passwords are case-sensitive.
Password:
Confirm Password:
Email Address
Please enter a valid email address for yourself.
Email Address:

Log-in

Human Verification

In order to verify that you are a human and not a spam bot, please enter the answer into the following box below based on the instructions contained in the graphic.



Click here to view the posting rules you are bound to when clicking the
'Submit Reply' button below


Additional Options
Miscellaneous Options

Click here to view the posting rules you are bound to when clicking the
'Submit Reply' button below


Topic Review (Newest First)
08-09-2002 07:46 PM
fer@fer
N hemispere binoc w compass not working in S?

Hi Bulleye,

Some principles of magnetism should be discussed to better understand what the vendor tried to explain.

The force of attraction magnetic field is greatest at the poles of the earth and least in the area between the two poles. The perfect place to be: Equator. The magnetic field is formed by lines of force flow from each of these poles, bending around and flow toward the opposite pole. Points of equal variation connected by an isogonic line, are plotted on Isogonic charts . In our navigation charts, we get only magnetic declination for the area. As we now, primarily correction for this, is the magnetic variation. In some places this variation is easterly; other places it is westerly.

The lines of force in the earth''s magnetic field pass through the center of the earth, exit at both magnetic poles, and bend around to re-enter at the opposite pole. Near the Equator, these lines become almost parallel to the surface of the earth. However, as they near the poles, they tilt toward the earth. In the immediate area of the magnetic poles they dip rather sharply into the earth. Since the poles of a compass tend to align themselves with the magnet lines of force, the magnet within the compass tends to tilt or dip toward the earth in the same manner as the lines of force.

Because the compass is suspended to swing freely, it tends to align with the earth''s magnetic lines of force. If you happen to be at North pole with a Southern calibrated compass, you''ll see that the card of the compass rose will almost point downwards. (And of course will get stuck, and will not longer free rotate as you change rumb.

This is known as the dip error: the compass card tends to align itself with the earth''s magnetic field. At or near the Equator this causes little or no problem, but as the ship nears either of the magnetic poles, the dip error (vertical dip in the needle) may become significant. In some areas, it may happen that the needle just dug itself into the bottom and wouldn''t read anything.

That is the main error for a compass in a ship. (In airplanes there are other errors in turning and acceleration, which I will skip discussing at this Honorable Sailing Forum)

How are these dip corrections managed by compass manufacturers: in compass for the Northern Hemisphere, a small counterweight is placed on the south seeking end of the compass needle, allowing the needle being parallel to the earth surface. In the Southern hemisphere the opposite applies and the counterweight is positioned on the north seeking end of the needle. That is the reason they only work in one hemisphere.

But, good compasses allow for this by allowing for a fairly large vertical play in the needle. But, the simple, flat compasses don''t work well in this situation because the tip of the needle hits the surface of the compass.

I recall one of the racing Cats racing The Race, changed compasses after entering Southern Hemisphere, since the needle plate got stucked.

Sorry so long, Regards

Fernando



08-05-2002 05:05 AM
DuaneIsing
N hemispere binoc w compass not working in S?

bullseye,

I will admit to my ignorance here. At first, I was going to reply that there should be no difference. Before posting, I decided to do a google search (amazing what you can find) and discovered that YES there is a difference.

In general, it comes down to using counterweights on the needles in compasses to account for the force which pulls one end of the needle down (toward the earth''s center). The vertical forces are opposite in the hemispheres and so different balancing is used.

I did find, however, at least one manufacturer that makes a compass which is claimed to work fine in either hemisphere. Also note that most of the references did not speak to binoculars specifically, but apparently they are affected, too.

Thanks for postng that question; I learned something.

Duane
08-04-2002 10:17 PM
bullseye
N hemispere binoc w compass not working in S?

hi,
i was in a binocular shop today & the salesperson warned me not to buy a pair of binoculars from the northern hemisphere(im in the southern hemisphere)ie, over the internet from the US or europe. he said the compasses required in the north or south hemisphere are different,he said a northern hemisphere binoculor with compass,that the compass would not work at all!

he said this after i told him i could buy over the internet at much cheaper prices than his.
i found the compass thing not working a little hard to believe.

was he right?, or was he just trying to make a sale?
any advice please

 
Posting Rules
You may post new threads
You may post replies
You may post attachments
You may edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is On


All times are GMT -4. The time now is 08:36 PM.

Add to My Yahoo!         
Powered by vBulletin® Version 3.8.7
Copyright ©2000 - 2014, vBulletin Solutions, Inc.
SEO by vBSEO 3.6.1
(c) Marine.com LLC 2000-2012

The SailNet.com store is owned and operated by a company independent of the SailNet.com forum. You are now leaving the SailNet forum. Click OK to continue or Cancel to return to the SailNet forum.