The compass is the boat’s most essential navigation instrument, designed to work reliably even when everything else fails. Therefore, there should always be a compass on the boat that is independent of a power source, along with nautical charts to avoid grounding and find your way.
What is a compass?
A compass is a navigation tool used to determine direction or heading relative to the magnetic North Pole. It operates using a magnetic needle suspended within a movable housing or casing, allowing it to move freely in all directions. The magnetic needle is typically marked with an N (north) and an S (south), and it always points toward the magnetic North Pole.
The compass doesn’t stand alone!
On a boat, a compass is usually used in combination with a chart so that the sailor can determine their position and heading concerning the desired destination.
Compass direction is a critical factor in navigation and sailing because it helps sailors avoid hazardous areas, find the shortest route to their destination, and maintain their course.
Different types of compasses
There are several types of compasses, but they all have in common the ability to tell us the course we are steering. Among the various compass types available are magnetic compasses, electronic compasses, and gyrocompasses, which use different technologies to determine direction.
How does a compass work?
A compass operates by utilizing the Earth’s magnetic field. The Earth acts as a large magnet, and the magnetic North Pole attracts the magnetic needle in the compass, causing it to point north.
In a magnetic compass, the magnetic needle is suspended on a pivot and can rotate freely. The needle is magnetic, so it always points to the magnetic North Pole.
As the compass is rotated, the magnetic needle continually adjusts its position to point north. This means that a sailor can determine their direction by observing where the needle points in relation to the compass’s markings. The compass can also be used to establish the heading if the direction to the destination and the current position are known.
Why does a compass point north?
A compass points north due to the Earth’s magnetic field. The Earth’s inner core consists primarily of molten iron, which is in constant motion. This movement generates a magnetic field around the Earth known as the geomagnetic field.
A compass functions by harnessing the Earth’s magnetic field. It contains a magnetic needle, which is a magnetic material capable of free movement.
How to use a compass?
Using a boat compass is straightforward. The compass is securely mounted and displays the direction the boat is heading.
When you want to read the direction, simply look directly down at the compass; the direction you are heading is indicated in degrees relative to north, which is zero.
What is a compass heading?
A compass heading refers to the direction that a boat or vessel is following, as determined by a compass. It is the direction read on the compass in degrees or points.
When specifying a compass heading, a commonly used reference is an angle relative to the magnetic North Pole or the compass’s magnetic rose. For example, a heading may be given as “heading 270 degrees” or “westward heading.”
Variation and Deviation
Variation and deviation are both factors that can affect the accuracy of compass directions and, thus, navigation and sailing.
Variation refers to the difference between the magnetic North Pole and the true North Pole, also known as variation. This difference is due to the Earth’s magnetic field and changes over time and location. Variation can be adjusted using a variation table that specifies the current variation for a specific area and season.
Deviation is another factor affecting compass direction. It is the difference between the magnetic North Pole and the direction the compass actually points when mounted on a vessel. This difference occurs due to magnetic disturbances on board the vessel, such as engines, electronics, or metal objects. Deviation can be corrected by performing compass adjustments that account for the vessel’s magnetic disturbances and adjust the compass accordingly.
Taking both variation and deviation into account is crucial during navigation and sailing to determine the exact direction and heading accurately. A precise compass heading is essential for avoiding hazardous areas, finding the shortest route to the destination, and maintaining the course.
Where can you buy a compass?
All boat supply stores sell compasses for pleasure boats.
Boat Compass Maintenance
Maintaining a boat compass is crucial to ensure its accuracy and reliability. Here are some essential points to consider:
Clean and protect: Regularly clean the compass to remove dust, dirt, or salt deposits. Use a soft cloth or sponge moistened with freshwater to gently wipe the compass. Avoid using chemicals or solvents as they can damage the compass. Also, make sure to protect the compass from direct sunlight, which can affect its accuracy.
I’ve had success using the product “Ultra Gliss” on a compass that had become matte and, therefore, hard to read.
Check the mounting: Periodically inspect the compass’s mounting to ensure it is stable and level. Make sure that mounting brackets are properly secured and that there are no loose or damaged parts. Any vibrations or shaking can affect the compass’s accuracy.
Adjustment: Over time, compass heading can be affected by variation and deviation. Learn how to calibrate your compass and periodically check if it is showing correct readings, cross-referencing with an electronic compass if necessary.
Check for magnetic disturbance: Examine your boat for any sources of magnetic interference, such as electronic equipment, engines, or metal objects. Try to position the compass in a location that minimizes such disturbances. If necessary, install a compass demagnetization device to reduce any magnetic disturbances.
Safety check: Regularly inspect the compass’s buoyancy and mobility. If you notice any leaks or air bubbles, get it repaired.
Spare parts: It can be a good idea to have some spare parts for the compass, such as mounting accessories or adjustment screws, in case they get damaged or lost.
Questions and Answers about the Compass
Who invented the first compass?
The magnetic compass as we know it today was developed in the 18th century and cannot be attributed to a single inventor. However, the first compass is believed to have been invented hundreds of years before the Common Era in China.
Can I rely 100% on a compass?
A compass is a reliable tool for determining directions, but it can be influenced by magnetic disturbances and deviation. It’s essential to calibrate and adjust the compass correctly and be aware of external factors that might affect its accuracy.
Can a compass be used to determine one’s exact position?
A compass alone cannot determine your precise position. However, it can be used in conjunction with other navigation methods such as chart reading to ascertain your position.