Parts-Syllabus
Part B
EM201 Advanced Navigation and Maritime Cyber Security
Magnetism.
Marine Magnetic Compass adjustment:position of equilibrium;

Marine Magnetic Compass adjustment:position of equilibrium;

Of course. This is an excellent and fundamental concept in marine magnetic compass adjustment. Let’s break down the “position of equilibrium” in a clear and structured way.

1. The Simple Definition

In the context of a marine magnetic compass, the position of equilibrium is the final, stable direction that the compass card (or needle) points to after all the magnetic forces acting upon it have balanced out.

In simpler terms, it’s where the compass needle actually settles and stops moving. This direction is what the helmsman reads as “Compass North,” and it forms the basis for the “Compass Course.”

2. The Forces at Play

The position of equilibrium is not determined by a single force, but by the resultant (the combined effect) of several magnetic forces.

There are two main categories of forces acting on the compass:

  1. The Directing Force: This is the force we want the compass to follow. It is the horizontal component of the Earth’s magnetic field, often denoted as ‘H’. On a perfectly non-magnetic ship, this would be the only force, and the compass would point directly to Magnetic North.

  2. The Deviating Forces: These are the forces we need to correct for. They originate from the ship’s own magnetism. This magnetism is a combination of:

    • Permanent Magnetism (Hard Iron): Magnetism “built into” the ship’s steel structure during construction. It acts like a permanent bar magnet attached to the ship.
    • Induced Magnetism (Soft Iron): Temporary magnetism induced in the ship’s soft iron components by the Earth’s magnetic field. This force changes as the ship changes its heading.

3. Equilibrium: The Tug-of-War

Imagine a tug-of-war.

  • Team A is the Earth’s magnetic field, pulling the compass needle towards Magnetic North.
  • Team B is the ship’s combined magnetic field, pulling the compass needle in a different direction.

The position of equilibrium is the final direction the rope (the compass needle) points when the two teams’ pulling forces have reached a balance. This final direction is almost never exactly Magnetic North on an unadjusted compass.

The angle between where the compass should point (Magnetic North) and where it actually points (the position of equilibrium) is called Deviation.

Position of Equilibrium = Compass North Deviation = The angle between Magnetic North and Compass North

Marine Magnetic Compass adjustment:obtaining and explaining the approximate coefficients A, B, C, D and E;Marine Magnetic Compass adjustment:principle of the deflector method and its limitation;