What causes compass deviation?

What causes compass deviation?

• A. The weather
• B. The motion of the vessel
• C. Metallic masses on the boat which cause a magnetic compass to give false readings
• D. The depth of water

Answer: (C)

Compass deviation comes from the ship’s own magnetic field interfering with the magnetic compass. The boat’s iron hull, engines, cables, and other metallic or magnetized equipment create local magnetic fields that push the compass reading away from true magnetic north. Because this interference depends on how the ship is oriented and what gear is active, the deviation changes with heading, which is why sailors use a deviation table after swinging the compass to correct readings. That’s why the best answer points to metallic masses on the boat causing the compass to give false readings. Weather, the motion of the vessel, or depth of water don’t produce this kind of persistent, heading-dependent error.

Compass deviation comes from the ship’s own magnetic field interfering with the magnetic compass. The boat’s iron hull, engines, cables, and other metallic or magnetized equipment create local magnetic fields that push the compass reading away from true magnetic north. Because this interference depends on how the ship is oriented and what gear is active, the deviation changes with heading, which is why sailors use a deviation table after swinging the compass to correct readings.

That’s why the best answer points to metallic masses on the boat causing the compass to give false readings. Weather, the motion of the vessel, or depth of water don’t produce this kind of persistent, heading-dependent error.