Course feed

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The course loading , also course conversion, is a conversion method used in the navigation of sea and aviation . A magnetic compass heading read from the magnetic compass is corrected with errors resulting from the difference between the geographic and magnetic north pole (magnetic declination ), deflection by magnetic fields on the ship ( deflection or deviation ), drift due to wind and drift due to current. This will actually be on pointing right (north geographically) is calculated based course or bearing values Nord. So the map course can be determined. Conversely, the map heading can be converted into the compass heading to be steered on the magnetic compass in this way. The term “course loading” comes from seafaring . The term "course conversion" is also used in aviation. The course loading is part of the nautical training at the nautical schools and various sports boat driving license exams.

Overview

Course (navigation) .svg

The graphic shows the relationship between the various courses of a ship:

1 - True North (rwN): true / geographically north
2 - true course (rwK): the direction in which the ship is pointing
3 - magnetic north (MgN): true north - declination
4 - compass north: true north - declination (6) - deviation (5)
5 - Deviation (Abl, DEV), due to the ship's own magnetic field
6 - Declination (Mw), due to the earth's magnetic field
7 - Compass course (MgK, CC), without correction of declination and deviation
8 - Magnetic course (mwK): Compass course corrected for deviation, but not with declination
9, 10 - drift due to wind (BW) and electricity (BS)
A, B - course over ground (KüG, COG).

Terms

German English meaning
MgK Magnetic compass heading CC Compass course Angle between Magnetic Compass North (MgN) and the ship's right orientation
Oj deflection DEV Deviation Angle between magnetic north (mwN) and magnetic compass north (MgN)
mwK magnetic course MC Magnetic course Angle between magnetic north (mwN) and the right alignment
Mw Magnetic declination DEC Declination Angle between true north (rwN) and magnetic north (mwN)
rwK right course TC True course Angle between true north (rwN) and the ship's right-hand alignment
BW Wind loading Angle between the true course (rwK) and the course through the water (KdW)
KdW Course through water Angle in relation to the water between the course and true north (rwN)
BS Charging by electricity Electricity-induced displacement from a cast to a true place
KüG Course over ground COG Course over Ground Angle between true north (rwN) and the direction of movement of the ship over the ground

Declination / magnetic declination

Since the magnetic poles of the earth do not coincide with the geographic poles, the magnetic field lines do not run exactly to the meridians that determine the north-south direction. In addition, certain geological formations divert the compass rose from the exact north-south direction. Because of the magnetic declination (Mw), a course taken from the map must not be steered directly on the compass. Likewise, a course read on the compass may not be transferred directly to the map.

Deviation / distraction

In addition, the compass needle is deflected by metallic components and magnetic fields on the ship. For example, from the engine below deck, from metallic superstructures, from the ship's hull itself, or from speakers that are mounted close to the compass. This influence is called distraction or deviation. Since these influences usually remain the same over a longer period of time, they can be measured and recorded in a distraction table. The deflection is taken into account in the course loading in the same way as the declination.

Loading with wind

see drift and wind triangle

Charging with electricity

In seafaring, the course charging is supplemented by charging with electricity in order to enable precise navigation. See current triangle .

practice

From compass to map

To put it simply, the course read on the compass is the magnetic course mwK. After filling the formula with the declination Mw, the correct course rwK is calculated from top to bottom while maintaining the sign , which can be entered on the map.

The deflection due to declination in the east is given a positive sign (+) when calculating the course. 

  mwK   45°
  Mw  + 12°      mit richtigen Vorzeichen von oben nach unten gerechnet
  rwK   57°

Accordingly, the magnetic declination in the west is given a negative sign (-). 

  mwK   120°
  Mw   -  4°     mit richtigen Vorzeichen von oben nach unten gerechnet
  rwK   116°

From the map to the compass

If a course is to be taken from the map and steered on the compass, it must also be converted taking into account the magnetic declination. Here the calculation is from bottom to top to determine the magnetic course or compass course. The opposite sign is now used for the calculation. 

  mwk   257°
  Mw    + 3°     mit umgekehrten Vorzeichen von unten nach oben gerechnet
  rwK   260°

Or: 

  mwK    85°
  Mw   -  6°     mit umgekehrten Vorzeichen von unten nach oben gerechnet
  rwK    79°

Simple memo scheme for conversion

In nautical charts, the declination is often represented graphically by an arrow on the compass rose:

  • ↗︎ eastern magnetic declination
  • ↖︎ western magnetic declination

The imaginary repositioning of this arrow pointing north ? leads to the compass heading.

Card course arrow Magnetic declination Compass heading Explanation
(True) (Var, Decl) (Compass)
057 ↗︎ 012 E 045 ? from map ↗︎ to compass ? -12 degrees

from compass ? to map ↗︎ +12 degrees

116 ↖︎ 004 W 120 ? from map ↖︎ to compass ? +4 degrees

from compass ? to map ↖︎ -4 degrees

And vice versa: The imaginary movement of the arrow from north ? to the magnetic declination (↖︎ or ↗︎) leads to the map course. The compass deviation (deviation) can of course be taken into account with the same scheme.

literature