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The standardcompass error

determination  

2014 Laurentiu - Marian Vieru 

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• 1st  Chapter - Introductoryconsiderations 

• 2nd Chapter - Procedures ofdetermining the compass correction

• 3rd Chapter - Case study.

Structure

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I n accordance with STCW, Section A-VI I I /2 (Watchkeeping

Standards), rule 34.2 :

“The standard compass error is determined at least once per watch and, when

possible, after any major alteration of course; the standard and gyro compasses

are frequently compared, and repeaters are synchronized with the master

compass.”  

Significance

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 The standard compass error is obtained by

comparing bearings using the following relation:

Δc = B(T) –  B(C)

δ  = Δc –  d

Δg = B(T) –  B(G)

What does it mean?

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With Transit Bearings (one alignment)

∆g = Ra –  Rg

Rm = Ra –  d

δ = Rm –  Rc

Checking the compass with coastal observations

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With equal bearing difference

Ra1 –  Rc1 = ∆c' 

Ra2 –  Rc12 = ∆c'' 

Ra3 –  Rc3 = ∆c''' 

∆c = ( ∆c'+∆c''+∆c''')/3 ; 

∆g = ( ∆g'+∆g''+∆g''')/3 

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With a star at one height

With Polaris Azimuth

With the Sun/Moon at rise and set

Checking the compass with astronomical

observations

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Conclusions 

•   The standard compass error determination, represent the day by day activity for

an officer of the watch, in calculating  Δc .

•   The standard error for gyro compass,  Δ g is calculated at grater periods of time,when is possible to apply more precise procedures; usually the gyrocompass is checked

by comparing it’s indications whit those of the magnetic compass.

•   For having a very small lateral alidade lean error, it is necessary that the star

we choose to have a small altitude.

•   It is recommended to execute simultaneously the standard error determination

 for both magnetic and gyro compasses.

•   To avoid errors caused by the time necessary to physically move the Alidade

 from the gyro repeater onto the magnetic compass,the next procedure is recommended:

One observer reads gyro bearing and relative bearing simultaneously.

 In the same time, another observer reads the compass heading of the ship.

 ∆g  is calculated:

 ∆g  = Ra  –  Rg , Az can be Ra; ∆c is calculated:

 Rcd = Rci + 180º

 Rc = Rp + Dc

 ∆c = Ra  –  Rc

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The standard compass

error determination  

Thank you !