Alfredo Contaldo · video

What this video covers

Navigating beyond 12 miles requires converting a true course plotted on a nautical chart into a compass heading by accounting for magnetic declination and deviation. Magnetic declination represents the angular difference between true north and magnetic north, which varies by location and year. Deviation is the error introduced by metallic objects on the vessel, which can be corrected using a deviation table or a professional compass compensator.

To convert a true course to a compass heading, subtract the declination and deviation from the true course. To correct a compass heading back to a true course, add these values. A simple mnemonic involves a three-step scale: true course at the top, magnetic course in the middle, and compass heading at the bottom. Descending the scale requires subtraction, while ascending requires addition. Annual updates to declination are calculated by multiplying the annual variation by the number of years elapsed since the chart's publication. Proper navigation requires using current, updated nautical charts rather than outdated editions.

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