MAGNETIC COMPASS

Magnetic Compass:

 

Is a vital instrument used to determine the direction a vessel is traveling relative to the Earth's magnetic field. It remains a crucial tool for navigation on the open seas, especially when electronic navigation systems (like GPS) fail or when operating in areas where GPS signals are weak or unavailable. Magnetic compasses are often used as a backup to more advanced systems and provide reliable, accurate heading information under most conditions.

 

How a Marine Magnetic Compass Works:

A magnetic compass uses the Earth's magnetic field to point toward magnetic north. It consists of a magnetic needle or card that is suspended or mounted on a pivot or gimbal system, allowing it to freely align itself with the Earth's magnetic field.

 

Magnetic Needle/Card: This component is made of a magnetized material and aligns with the Earth's magnetic field.

 

Card: The compass card, which is often marked with degrees (360°) or directions (N, S, E, W), rotates as the vessel changes heading.

 

Gimbals: These are pivoting rings that allow the compass to remain level regardless of the ship's movement, keeping it horizontal and stable even in rough seas.

 

Types of Marine Magnetic Compasses:

 

Standard Magnetic Compass:

 

Description: This is the simplest form of a magnetic compass. It consists of a magnetic needle or card, with a basic housing to protect it from the environment. It’s often used on smaller vessels.

Advantages: Simple, low cost, no power required.

Uses: Small boats, recreational vessels, backup system on larger ships.

Disadvantages: Can be affected by nearby magnetic interference from electronics or metal objects.

 

Fluid-Damped Magnetic Compass:

 

Description: This type of compass is similar to the standard magnetic compass but is filled with a fluid (such as oil or alcohol) to dampen the oscillation of the compass card. This helps in stabilizing the needle and providing smoother readings.

Advantages: Smoother and more stable readings, less affected by the movement of the vessel.

Uses: Recreational boats, yachts, and medium-sized vessels.

Disadvantages: Still susceptible to magnetic interference, fluid can leak or evaporate.

 

Steering Compass (Card Compass):

 

Description: A steering compass is a more precise, larger type of magnetic compass designed specifically for use in the wheelhouse to provide accurate heading information for steering. These compasses often have a large, easy-to-read dial.

Advantages: Provides very accurate heading readings, suitable for steering a vessel on long journeys or in difficult conditions.

Uses: Commercial vessels, larger yachts, and ships.

Disadvantages: Larger and bulkier, more expensive than basic compasses.

 

Gyrocompass:

 

Description: While not strictly a magnetic compass, a gyrocompass uses the principles of a gyroscope to find true north (as opposed to magnetic north). It’s widely used in modern navigation systems for its high accuracy.

Advantages: Provides true north, unaffected by magnetic fields, more accurate than magnetic compasses.

Uses: Large commercial vessels, military, and high-end leisure vessels.

Disadvantages: Expensive, requires power supply and maintenance, not a "magnetic" compass per se.

 

Navigator Compass (Fluxgate Compass):

 

Description: A fluxgate compass is an electronic compass that uses a magnetometer to measure the magnetic field's direction and strength. It provides digital output and can be integrated with other navigation systems.

Advantages: More precise than traditional magnetic compasses, often used in automated systems, can be integrated with GPS, autopilot, etc.

Uses: Commercial vessels, large yachts, advanced navigation systems.

Disadvantages: Requires power, can be affected by nearby electronic devices.

Factors Affecting Marine Magnetic Compass Accuracy:

 

Magnetic Deviation:

Every vessel has magnetic materials (like steel, motors, or electronics) that can create their own magnetic fields, which interfere with the Earth's magnetic field. This causes magnetic deviation, where the compass reading is inaccurate due to the vessel’s internal magnetic influences.

Correction: A deviation table is created by adjusting for known deviations at different headings to help correct compass readings.

 

Magnetic Variation (Declination):

The Earth's magnetic field doesn’t align exactly with the geographic poles. This creates magnetic variation or declination, the angle between geographic (true) north and magnetic north.

Correction: Mariners need to apply the local magnetic variation to get true headings, which changes depending on the vessel's location.

 

Gyroscopic Precession (in Gyrocompasses):

Gyrocompasses, although more accurate, can suffer from precession (the gyroscope’s slow drift), which requires periodic adjustments or recalibration.

 

Top Brands of Marine Magnetic Compasses:

 

Plath:

Known for high-quality, durable compasses used in commercial and recreational vessels.

Popular Models: Plath Master Compass, Plath Gimbaled Compass.

Features: Fluid damped, easy to read, highly accurate, and resistant to magnetic interference.

 

Danforth:

One of the most popular brands for recreational boat compasses, especially on smaller vessels.

Popular Models: Danforth Constellation Compass.

Features: Fluid damped, highly visible, reliable, and affordable.

 

Ritchie Navigation:

Ritchie is one of the most well-known brands for both recreational and professional marine compasses.

Popular Models: Ritchie PowerDamp, Ritchie Voyager, Ritchie Helmsman Series.

Features: Excellent durability, fluid damping, and large, easy-to-read dials.

 

C. Plath:

A German manufacturer known for making high-precision, durable compasses for commercial vessels and yachts.

Popular Models: C. Plath Master Compass, C. Plath Yacht Compass.

Features: Fluid-damped, shockproof, high accuracy, and often used in luxury yachts and large vessels.

 

Suunto:

Known for producing reliable and compact compasses, used in both marine and land navigation.

Popular Models: Suunto SK-8 Compass (compact model often used for smaller boats and backup purposes).

Features: Durable, highly accurate, and often used in smaller vessels.

 

Kongsberg (Norway):

Kongsberg offers advanced solutions for marine navigation, including gyroscopic and fluxgate compasses, along with magnetic compasses for large vessels.

Popular Models: Kongsberg Marine Compass Systems (mainly for commercial and military ships).

Features: Precision, integration with other navigation systems, and robustness.

 

Binnacle Compasses (Various Manufacturers):

 

The Binnacle compass is often used as a central navigation instrument on the bridge of a vessel. It’s a larger, mounted compass housed in a binnacle (a structure designed to protect the compass).

Features: Offers large, easy-to-read dials with fluid damping, and can come integrated with more advanced systems.

 

Conclusion:

Marine magnetic compasses are essential for safe navigation, especially when technology or GPS is unavailable. The right compass depends on the type of vessel, its size, and the complexity of its navigation system. Smaller vessels can rely on simple, fluid-damped magnetic compasses, while commercial ships often need more precise, large, and robust compasses like steering compasses or gyrocompasses.