[Ozee Adventure]

"Get comfortable with the concepts of variation & deviation!!!"

I'm not asking anyone to do my homework for me - I'll be searching for a paragraph & picture for each thing I have to learn (14 week course) – that’s how I do best.
I'll leave it here for others who are learning too.

[Ozee Adventure]

Compass error is the combination of error caused by magnetic variation, and error caused by magnetic deviation.

Variation is an effect of the Earth's magnetic field at a particular location, which causes a compass needle to deflect relative to true north, or to an angle to the meridian.

Deviation is the magnetic influence on a compass caused by the construction materials of a vessel and installed equipment, and varies with the vessel heading.

[mad]

What qualification do you get when you finish?

[Ozee Adventure]

mad, on Feb 14 2008, 07:29 PM, said:

What qualification do you get when you finish?

RYA Day Skipper so I can get on with the coastal stuff - there are some basics I need to know to be a pirate!

[mad]

14 weeks for day skipper???

go straight for your coastal, its easy

[Ozee Adventure]

mad, on Feb 14 2008, 07:36 PM, said:

14 weeks for day skipper???

go straight for your coastal, its easy

3 hours a week - they wouldn't let me go straight there - I need my basic nav stuff

[savoir]

You can come and turn my compass anytime.

If you know all about deviation does that make you a deviate ?

[mad]

Ozee Adventure, on Feb 14 2008, 01:40 AM, said:

3 hours a week - they wouldn't let me go straight there - I need my basic nav stuff

Fair enough, just remember, no television till you've done your homework

[Ozee Adventure]

mad, on Feb 14 2008, 08:38 PM, said:

Fair enough, just remember, no television till you've done your homework

:lol: Happy to plod in some ways but I want to know stuff ready to play on the VO 60 in January!

[Ozee Adventure]

VARIATION
This is the name given to the error caused by the difference in position between the true and magnetic poles. As its name denotes, it varies from place to place across the world, but it is accurately tabulated for the navigator's use. It can be described as follows:

Variation is the error in the compass caused by the Earth's magnetism. It is always named E or W according to which direction the card is deflected away from true north.

TO FIND VARIATION ERROR
On every chart there are a number of compass roses as described in next paragraph below. In the centre of each compass rose is listed the variation for that area and the amount it is likely to change in one year, which is usually fairly small

THE COMPASS ROSE
Since most navigation on a chart involves the use of the compass, a reproduction of a compass card is printed at strategic points across the face of every chart. These are termed compass roses and their positioning is such that there is always one close to hand no matter where on the chart the navigator is working. They are graduated in three-figure notations from 0° to 360° and contain details of the variations in force in that area.


 comrose1.jpg (39.18K)
Number of downloads: 7

[Ozee Adventure]

DEVIATION
The second of the two errors which affect the magnetic compass, deviation, is caused by the magnetic influence of anything near the compass needle. Someone placing a metal knife alongside the binnacle, for example, will cause a deflection of the compass needle and result in deviation error. Steel in the construction of the ship, electric circuits, motors, and so on, can all affect the compass and create a deviation error. It would be safe to describe this error as follows:

Deviation is the error in the compass caused by the ship's magnetism. It is always named E or W according to the direction the card is deflected from true north.

TO FIND DEVIATION ERROR
This is not so easy. To begin with, new fittings, new stores or new equipment placed on the ship can add to the error of deviation. Providing the new products are not too magnetic and they are kept at least 1 metre away from the compass binnacle, they should not have too much effect, and this is worth remembering when fitting out a ship. The deviation can be affected with each change in the ship's direction, which creates another problem. Finally, the ship itself, particularly if it is of steel construction, will have become a magnet in its own right during its building period and, as can well be imagined, this will play havoc with the accuracy of the compass in the binnacle.
The best way to find the deviation error is to engage a professional compass adjuster (Certified Compass Engineer) and have him attempt to eliminate the error or, if it cannot be eliminated, tabulate it on what is known as a deviation card.

THE DEVIATION CARD
When a ship is checked for deviation it must be checked on all headings since, as mentioned, deviation varies according to the course being steered. The Compass Engineer will swing the ship through the major compass points and determine the deviation on each point. The Compass Engineer will then list the deviation error on each heading on a deviation card. Thus the navigator can, by referring to this card, determine the deviation error on whatever course is being planned


 devcard.jpg (8.27K)
Number of downloads: 12

[Lazy Guy]

Ozee Adventure, on Feb 14 2008, 01:32 AM, said:

RYA Day Skipper so I can get on with the coastal stuff - there are some basics I need to know to be a pirate!

Do you have to get wet for that?

:P

[GybeSet®]

savoir, on Feb 14 2008, 09:12 PM, said:

You can come and turn my compass anytime.

If you know all about deviation does that make you a deviate ?

you 'swing' compasses, well unless the other side has another method ?

[fastwhenwet]

Here is a little saying to help in the math when uncorrrecting from true to compass:
T rue
V irgins
M ake
D ull
C ompanions

add W hiskey

[Ozee Adventure]

fastwhenwet, on Feb 15 2008, 07:49 AM, said:

Here is a little saying to help in the math when uncorrrecting from true to compass:
T rue
V irgins
M ake
D ull
C ompanions

add W hiskey

I'll take this one back to school & see what response I get!!!
Thanks :lol:

[Ozee Adventure]

fastwhenwet, on Feb 15 2008, 07:49 AM, said:

Here is a little saying to help in the math when uncorrrecting from true to compass:
T rue
V irgins
M ake
D ull
C ompanions

add W hiskey

Now I can correct & uncorrect!
C adbury's
D airy
M ilk
(tastes)
V ery
N ice

[mad]

hows the homework?

Need help with your lines