Marine Magnetic Compass adjustment:use of the Kelvin deflector;

Of course. Here is a detailed explanation of the Kelvin Deflector and its use in marine magnetic compass adjustment.

Marine Magnetic Compass Adjustment: Use of the Kelvin Deflector

The Kelvin Deflector is a specialized instrument used for adjusting a ship’s magnetic compass, specifically for correcting semicircular deviation, without the need to “swing the ship” (i.e., turn the vessel through 360 degrees). It is a clever, time-saving tool, though it has specific applications and limitations.

1. What is the Kelvin Deflector?

Named after its inventor, Lord Kelvin, the deflector is a device that fits precisely on top of the compass bowl. It consists of:

• A pair of small magnets: Housed within the instrument, these magnets can be moved closer to or further from the compass needles by turning a graduated knob or drum on the side.
• A graduated scale: This scale indicates the position of the internal magnets, allowing the user to apply a known, repeatable magnetic force.
• A prism or sighting vane: This allows the user to accurately observe the compass card while the deflector is in place.

The fundamental principle is that the deflector introduces a known, artificial magnetic field to the compass. This artificial field is used as a reference to measure and then cancel out the ship’s own magnetic field.