Help with marine navigation!!!!!!!!!!!?

Question

iam studying star sights for college,after i have,truecompass,gyrocompass,error,varia... not sure whats the rule is for calculating deviation.

Answer 1

Mark has the right way for getting a Deviation Table.  

Deviation is caused by iron and steel in the vessel's structure and equipment.  

Magnetic Deviation is the difference between Magnetic Bearings and Compass Bearings. Deviation varies for every compass in the same location and depends on such factors as the magnetic field of the boat, wrist-watches, etc. The value will also vary depending on the orientation of the boat.

If you have a magnetic of 300 degrees and your compass reads 305 degrees you have a westerly deviation of 5 degrees.    

If you have a compass reading of 045 degrees and your deviation card says you have a 3 degree easterly deviation for that heading the magnetic would be 048 degrees.  

Good Luck and Boat Safe !

(btw I have sextant here that has not been out the case for years now that there is GPS)  

Answer 2

deviation is the error of your magnetic compass. The only way to correct that is to "Swing the compass" where a compass adjuster comes out and points the boat in all directions and notes the compass error as compared to an adjusted compass that he has. He then can try to correct some of this out with adjustments to your compass and also makes up a deviation table for your compass at different headings. Remember this saying: True Virgins Make Dull Company, or TVMDC. It means: True plus or minus Variation = Magnetic plus or minus Deviation = Compass

Answer 3

Lots of good answers on Deviation here, but your question mentioned star sights, so I'm assuming you're computing an azimuth or amplitude to a body and being asked to determine deviation from that. Given your True bearing (the azimuth, whether computed directly or derived from an amplitude) add your west Variation or subtract your east Variation (it will either be given in the problem, or printed on the chart in the compass rose) to obtain your Magnetic bearing. Compare this to the bearing to the object read on your steering compass, the difference is your Deviation, ON THIS HEADING. Once your deviation is known for this heading, on this heading use the same deviation for all bearings. Lots of USCG test questions try to trip you up on this.

There is no such thing as Deviation on a gyrocompass, that is a "distractor".

It's rare that I disagree with Captain Bill, but I take my sextant with me on any ocean crossing. GPS is great when it works, but when it doesn't I still want to get home.

Answer 4

TVMDC.

True

Variation

Magnetic

Deviation

Compass

(adding West variation and deviation)

This is the correction for getting your compass reading.  If you are uncorrecting (that is to get the true reading, you will minus the west variation and deviation)

If you know your compass reading, the true reading and the compass deviation (or error), you can determine the variation.  See example

True = 87 degrees

Compass = 72 degrees

Deviation (or compass error) = 4 degrees west

Variation = X (if positive, variation is West, if negative it is East)

87      True

+X      Variation

87 + X Magnetic

+4      Deviation

72      Compass

87 + X + 4 = 72

or

X = 72 + 4 - 87

therefore:

X = - 11

since negative the variation would be East 11 degrees

You can substitute for deviation the same way.  I noticed you had been looking for th ecompass deviation (error)

Answer 5

your back up gps ,ha ha just kidding.   I never learned it much mind bending.