Magnetic Compass: Essential Questions for MCA Orals
Welcome to your go-to resource for Magnetic Compasses in MCA Orals preparation! This page is dedicated to providing comprehensive links and materials focused on the essential topic of magnetic compasses, designed specifically to help Officer of the Watch and Master Mariner candidates excel. Make sure to check back frequently as we continuously update with new questions, detailed answers, and valuable resources to support your study journey. Your success is our priority!
What is a magnetic compass and how does it work?
A magnetic compass is a navigational tool that shows direction relative to the Earth's magnetic poles. It consists of a magnetized needle or card that aligns with the Earth's magnetic field, pointing towards magnetic north.
What is deviation in a magnetic compass?
Deviation is the error caused by magnetic influences within the vessel itself. It varies with the ship's heading and must be corrected using correctors.
What are quadrantal spheres and their function?
Quadrantal spheres are soft iron balls placed on either side of the compass to correct quadrantal deviation, which occurs due to the interaction of the ship's magnetic field with the Earth's magnetic field at different headings.
Define semi-permanent magnetism
Semi-permanent magnetism varies with the ship's heading and environmental factors such as latitude and temperature. It requires adjustable correctors for compensation.
How do you use a deviation card?
A deviation card lists known compass deviations for various headings. It is used to correct compass readings by adding or subtracting the listed deviation from the compass heading
What are the steps to take if the magnetic compass becomes defective during a voyage?
Use alternative navigation methods such as gyrocompass, GPS, or celestial navigation. Report the defect to the bridge and follow the ship's safety procedures to repair or replace the compass as soon as possible
How do you use a gyrocompass in conjunction with a magnetic compass?
The gyrocompass provides true north, which can be cross-referenced with the magnetic compass to identify and correct deviations. It is especially useful in high latitudes where magnetic variation is significant
How does the Earth's magnetic field change with latitude?
The magnetic field's inclination varies with latitude, being more vertical near the poles and horizontal near the equator. This affects the vertical component of the ship's magnetism.
What are the main components of a magnetic compass?
The main components include the magnetized needle/card, pivot, damping fluid, and compass rose. These parts work together to provide accurate directional readings.
How do you calculate compass error?
Compass error = True Bearing - Compass Bearing. Measure the bearing of a known object, check the true bearing from the chart, apply the local variation, and subtract the compass bearing to find the error.
Explain the term 'heeling error' and how it is corrected
Heeling error occurs when the ship tilts due to wave action or turning. It affects the vertical component of the ship’s magnetism. It is corrected using a heeling error magnet placed below the compass
Why is it important to perform regular compass swings?
Regular compass swings help identify and correct deviations, ensuring the compass provides accurate directional information for safe navigation
How do you determine the magnetic variation for a given area?
Magnetic variation is found on nautical charts. It shows the annual change and current variation, which should be applied to true bearings to convert them to magnetic bearings.
How can you verify the accuracy of a magnetic compass?
Cross-check compass readings with known landmarks, celestial bodies, or electronic navigation aids. Perform regular compass swings and maintain an up-to-date deviation card
Describe the procedure for taking a bearing with a magnetic compass
Sight the object through the compass’s sighting device, align the compass card, and read the bearing. Correct the reading for deviation and variation to determine the true bearing.
Explain how a magnetic compass is aligned during installation.
Align the compass with the ship's fore-and-aft line, ensuring it is level and free from nearby magnetic influences. Perform a compass swing to check for deviations and adjust as necessary.
Explain the term 'variation' in the context of a magnetic compass.
Variation is the angle between true north (geographic) and magnetic north. It varies depending on geographic location and is indicated on nautical charts.
What is the purpose of the Flinders bar?
The Flinders bar is used to correct induced magnetism in the vertical plane. It is adjusted based on changes in the Earth's magnetic inclination, especially when changing hemispheres.
What is permanent magnetism and how does it affect the compass?
Permanent magnetism is the magnetism retained by the ship due to construction processes. It affects the compass consistently and is corrected using permanent magnets placed around the compass
What is the role of a compass adjuster?
A compass adjuster is a qualified individual who calibrates and corrects the compass by adjusting correctors and performing compass swings to minimize errors.
Explain the importance of damping fluid in a magnetic compass.
Damping fluid stabilizes the compass needle, preventing it from oscillating excessively. This ensures a steady and readable compass card, especially in rough seas.
What factors can cause permanent magnetism in a vessel?
Factors include the construction process, welding, and alignment with the Earth's magnetic field during the build. Permanent magnetism affects the compass and requires correction using permanent magnets.
Explain the impact of cargo on magnetic compass readings
Certain cargoes, especially those containing iron or steel, can create localized magnetic fields that affect compass readings. Ensure that cargo is stowed in a way that minimizes its impact on the compass
What is the significance of a ship's magnetic signature?
A ship's magnetic signature is the total magnetic influence it has, including permanent and induced magnetism. It affects the accuracy of the magnetic compass and must be regularly monitored and corrected