What is Degaussing?
Degaussing is the process of reducing or eliminating a magnetic field from a magnetic object. On ships, degaussing aims to neutralize the magnetic fields produced by the ship itself, which could trigger underwater mines designed to detonate when detecting a magnetic anomaly.
The concept of degaussing ships was first developed in the early 20th century, when naval mines that could be trigged by a ship’s magnetic field started coming into use. The British Royal Navy is credited with pioneering degaussing to protect its ships during World War I.
The purpose of degaussing on ships is to counteract and cancel out the magnetic field naturally generated by the ship’s steel hull and machinery. By installing degaussing coils around the hull of a ship and running electrical currents through them, an opposite magnetic field can be created that brings the ship’s total magnetic field close to zero. This reduces the risk of the ship triggering magnetically-fused mines and keeps the vessel and crew safe.
Sources: https://navymuseum.co.nz/explore/by-themes/technology-and-weapons/degaussing-2/, https://www.quora.com/What-is-the-purpose-of-degaussing-coils-on-ships
How Do Degaussing Systems Work?
Degaussing systems work by creating a powerful electromagnetic field around a ship. This field neutralizes or “masks” the magnetic field of the ship itself. According to Ontrack, “The physical principle underlying the degaussing relies on the polarization of the Weiss domains.”
Specifically, degaussing systems consist of electrical coils that are installed around the circumference of a ship’s hull, usually encased in fiberglass mounts. When activated, these coils produce a magnetic field strong enough to cancel out the magnetic field emitted by the ship. This process removes any residual magnetism and prevents the ship from triggering magnetic mines and torpedo detonators.
The coils are connected to a degaussing control station that allows operators to adjust the electrical current passing through the coils. This allows the magnetic field to be tuned precisely to counteract the ship’s specific magnetic signature at any given time. The degaussing system must be recalibrated periodically as ships accumulate magnetic fields over time from traveling through Earth’s magnetic field.
Types of Degaussing Systems
There are several types of degaussing systems used to reduce or eliminate unwanted magnetic fields from ferromagnetic objects:
Permanent Degaussing
Permanent degaussing, also known as “hard degaussing,” involves applying a strong magnetic field from coils mounted around the ship’s periphery. This induces a permanent magnetic field in the ship that offsets and neutralizes the ship’s inherent field (Wikipedia). Permanent degaussing provides continuous protection against magnetic mines and is commonly used on steel-hulled military, commercial, and private ships.
Transient Degaussing
Transient degaussing, or “wipe degaussing,” uses removable degaussing coils powered from an external electric power source to induce a reverse magnetic field and erase a ship’s permanent magnetic field. It is a temporary effect used when a ship needs to be degaussed quickly in response to immediate threats (Royal New Zealand Navy Museum).
Wiping
Wiping involves moving a degaussing coil over the surface of a magnetic storage device like a hard disk drive to disrupt and randomize the magnetic domains. This erases any data stored on the device (Wikipedia).
Comparison of Types
Permanent degaussing continuously protects ships from magnetic mines, while transient degaussing temporarily erases a ship’s magnetic signature. Wiping uses localized degaussing coils to erase data from magnetic storage media. Permanent and transient degaussing are used on ships and vessels, while wiping is used specifically for data destruction.
Degaussing System Components
The main components of a degaussing system include:
Control Equipment
The control equipment regulates electrical current to the degaussing coils to neutralize the ship’s magnetic field. This includes control panels, automatic controllers, and manual controllers to activate the degaussing system as needed [1].
Sensors
Fluxgate sensors located at strategic points on the ship measure the ambient magnetic field around the hull. They provide feedback to the control equipment to adjust the degaussing coils as needed to cancel out the ship’s magnetic signature [2].
Degaussing Coils
Degaussing coils are wrapped around the hull and positioned to generate magnetic fields that counteract the ship’s magnetic field. When energized, the coils neutralize the magnetic signature of the steel hull. The coils can be oriented vertically, horizontally, or in rings to optimize the canceling effect [3].
Power Supplies
The degaussing coils require a high-voltage power source, often rated at several hundred volts DC. This enables the system to produce the strong magnetic fields needed for effective degaussing while the ship is underway.
Installing a Degaussing System
Installing a degaussing system on a ship requires careful planning and execution. According to the U.S. Navy’s technical manual on degaussing systems, there are several key considerations when installing a degaussing system:
The degaussing coils must be located at specific positions along the length of the ship. The forward (“A”) coil is installed approximately 10% of the ship’s length from the bow. The aft (“B”) coil is installed approximately 10% of the ship’s length from the stern. The athwartships (“C” and “D”) coils are installed on the port and starboard sides amidships [1].
The degaussing system requires extensive electrical wiring throughout the ship to connect the coils to the control panel. Cables must be properly shielded and grounded to prevent interference. Degaussing cables follow separate routes from other electrical wiring and are specially marked for identification [2].
All connections between the degaussing coils, control panel, and power supply must be properly terminated and tested. Precise electrical phasing between the coils is critical for effective degaussing. The system is designed to precisely cancel out the ship’s magnetic field [3].
Proper installation requires coordination between electricians, technicians, and shipyard engineers. Once installed, the degaussing system must be calibrated and adjusted to tune it to the specific magnetic signature of the ship.
Operating and Maintaining Degaussing Systems
Proper operation and maintenance are critical for degaussing systems to function reliably. This involves regular testing, calibration, monitoring, and troubleshooting.
Degaussing systems should be tested and calibrated periodically to ensure they are operating within specifications. This may involve activating the degaussing coil and measuring the magnetic field to verify performance. Calibration keeps the system adjusted for optimal effectiveness.
While in use, the degaussing system needs ongoing monitoring to catch any performance issues early. The control equipment, coils, sensors, and power supply should be checked regularly for problems. Monitoring data like voltage, current draw, and magnetic field readings can indicate if something is amiss.
If erratic behavior or failures occur, troubleshooting is required to diagnose and fix the problem. Common issues include control malfunctions, defective coils, broken sensors, and power supply disturbances. The degaussing control logs and monitoring data help pinpoint the source of troubles.
With proper care and maintenance, degaussing systems can operate reliably for many years protecting ships from magnetic threats. Regular upkeep activities like testing, calibration, monitoring, and troubleshooting are essential to maximize uptime and performance. For complex issues, specialized technicians may be needed.
As noted in “Use and Care of Electromagnetic Degaussers” (https://www.semshred.com/explore/insights/learning-library/use-and-care-of-electromagnetic-degaussers/), factory authorized experts should service and maintain degaussing systems when needed.
Advantages of Degaussing
Degaussing systems offer several key advantages for naval ships:
Reducing Magnetic Signature
Degaussing reduces a ship’s magnetic field to near zero levels, which helps minimize its magnetic signature. This makes the ship much harder to detect by naval mines that are triggered by magnetic influence. It also makes the vessel less noticeable to magnetic anomaly detection equipment used to spot submarines. Degaussing is a key way that naval ships can become stealthier and less susceptible to enemy detection.
Protecting Against Mines
By reducing a ship’s magnetic signature, degaussing offers critical protection against influence mines, which are designed to detect a ship’s magnetic field and detonate when it passes by. Degaussing disables this triggering mechanism, allowing navies to navigate minefields more safely. This protects ships and crews from dangerous underwater explosives.
Allowing Safe Navigation
The ability to safely transit through mined waters or approach potentially hostile coastlines is essential for naval mobility and flexibility. Degaussing enables this by minimizing magnetic signatures that would otherwise alert mines or detection systems. This freedom of navigation allows naval ships to maneuver as needed for operations, without being constrained by magnetic threats.
Overall, degaussing provides major advantages for naval vessels in terms of stealth, defense, and operational maneuverability. This makes it an indispensable capability for modern navies.
Limitations of Degaussing
While degaussing is an effective system, it does have some limitations:
Degaussing does not remove a ship’s permanent magnetization. It simply reduces the magnetic field. This means degaussing does not make a ship fully non-magnetic. Residual magnetization will remain unless very strong degaussing fields are applied continuously.1
Degaussing systems require regular recalibration, known as swinging the ship, to ensure they are operating properly. This involves turning the ship in different directions to determine the proper compensation for the ships’ current magnetic state.1
Degaussing offers no protection against non-magnetic influence mines. These mines detect targets through acoustic, magnetic-acoustic, pressure, or vibration effects instead of magnetism alone.
Degaussing Standards and Regulations
There are several standards and regulations surrounding degaussing systems and technology:
The International Magnetics Organization (IMO) has published standards for degaussing systems, including IMO A.170 and IMO A.231. These specify performance requirements and test methods for degaussers intended for purging magnetic signature from ships.
The United States Navy has its own standards and specifications for degaussing warships, including MIL-STD-2042 and NSA/CSS 9-12. These outline requirements for magnetic signature reduction and measurement.
Degaussers must undergo rigorous testing and certification to verify they meet the required standards. Certification bodies like NSA Information Assurance evaluate and validate degausser performance before approving them for use in sensitive applications.
Compliance with degaussing standards is crucial for proper sanitization and ensuring no residual magnetic data remains on storage media.
The Future of Degaussing
Degaussing technology continues to advance as navies around the world look to counter new threats and use new shipbuilding materials. Some key areas of development include:
New degaussing technologies like high-temperature superconducting coils are being researched to create more powerful magnetic fields for degaussing. These new coils can operate at higher power levels and generate stronger counteracting fields than conventional copper coils (source).
As navies build ships out of non-steel materials like aluminum, titanium, and composites, effective degaussing gets more challenging. New methods are being studied to degauss these non-magnetic hulls and prevent magnetic signature detection (source).
Advanced monitoring systems are being developed to provide real-time feedback on a ship’s magnetic signature while underway. This allows the degaussing system to be dynamically adjusted to optimize the counteracting field for the conditions (source).