A nautical compass is a fundamental navigation tool that has been used by seafarers for centuries. It's primarily known by sailors as the compass, which can also refer to the magnetic compass, used to find direction, and the lubber's line on the compass rose for indication of ship's heading.
However, in broader maritime usage, the term 'compass' can encompass several variations, often distinguished by their design and function. For instance, the binnacle compass is the kind of compass typically affixed to the ship's bulkhead or console, whereas the magnetic compass is an ancient marine navigation instrument that uses the Earth's magnetic field to indicate direction.
Types of Nautical Compasses
The most common nautical compass, the magnetic compass, utilizes the Earth's magnetic field to point north. However, other compass types are employed for specific purposes:
The Binnacle Compass, a common fixture in the wheelhouse or navigation station of ships, is the primary navigation tool, mounted in a small cabinet called a binnacle. It's specifically designed to keep the compass spaced and easily readable, offering an accurate course reading.
Deck Compasses
Deck compasses are partially idiot-proofed for convenience and quick reference. They're typically placed on the wheelhouse deck or on the ship's bridge for nautical adventurers to quickly check their heading.
Deck compasses often feature an index line, a line or series of dots to help align the compass with the direction of the ship's motion. This helps confirm the lubber's line, which shows the ship's current direction, is correctly set.
Celestial Compasses
Celestial compasses use the position of stars and planets to determine the vessel's direction. Some, like the Davis Dial, can provide accurate readings when perpendicularly observing a celestial body through the device's sights.
The sextant, another celestial compass, uses the reflection of two images in its lens to find the angle of elevation from the horizon to a celestial body. With this information, one can formulate their position using the Nautical Almanac.
Care and Maintenance of Nautical Compasses
Proper care and maintenance is crucial for nautical compasses to function accurately. Regular recalibration is necessary to prevent the compass from becoming de-magnetized over time.
Environmental factors such as metallic objects, electrical currents, and magnetic influences can affect compass readings. It's important to minimize these influences around your compass and follow standard procedures to care for and maintain it.
De-Clinating the Compass
To ensure accurate navigation, it's essential to account for the magnetic variation, or deviation, of the compass. De-clinating the compass involves noting the magnetic north's direction versus true north to avoid accuracy alternations in the compass's influence.
A good safety tip is to correct such variations every time you navigate in a new magnetic environment. This can be done by analyzing a magnetic exploration map or the 'declination' entry in the almanac, providing local magnetic north's angle re-true north.
Calibration
Calibration is a periodic check to ensure the compass maintains proper accuracy. It ought to be done at sea, with the vessel static and away from magnetic distractions, and often enough to protect against the effects of natural magnetic permutations.
Calibration can be carried out using a known fixed point or by deducing a reference direction from landmarks or star sights. Usually, recalibration is necessary when any significant magnetic condition changes, such as geographical position or weather conditions affecting the Earth's magnetic field.
Understanding your compass, its varied types, and how to maintain it is crucial for safe navigation. It's a slips rule of thumb that good seamanship still depends heavily on regular drills and continuous education on your compass and other essential navigation tools.