HMAS Melbourne makes amend of her magnetic ways

Published on Mr Pup Elliott (author), CPO Sky McPhee (photographer)

Location(s): HMAS Stirling, WA

Topic(s): HMAS Stirling, HMAS Melbourne (F05)

HMAS Melbourne undergoes deperming at the Magnetic Treatment Facility at Fleet Base West, Garden Island, Western Australia. (photo: CPO Sky McPhee)
HMAS Melbourne undergoes deperming at the Magnetic Treatment Facility at Fleet Base West, Garden Island, Western Australia.

The next Royal Australian Navy ship to see service in the Middle East Area of Operations has undergone an important treatment in Western Australia before sailing for foreign seas.

HMAS Melbourne entered the Magnetic Treatment Facility at Fleet Base West in order to undertake deperming in the first week of September. The Magnetic Treatment Facility located at HMAS Stirling is the only facility in Australia capable of performing the deperming function.

Deperming is the minimisation of a ship's magnetic signature. The Magnetic Treatment Facility at HMAS Stirling provides the capability to reduce, alter and stabilise the permanent magnetism in steel hulled vessels, thereby minimising mine threats and magnetic detection.

Magnetic treatment involves wrapping large cables around the hull, forming a solenoid to induce a controlled longitudinal field into the vessel. The vessel is then berthed in the Magnetic Treatment Facility which also has a built in coil to generate a vertical magnetic field. By controlling the current (and hence the magnetic field) in both of these coils, significant reduction in the permanent magnetisation can be achieved.

The requirement for this process arose due to the evolving development of magnetic sea mines in World War II. Normally these fields are reduced by the onboard degaussing system, however, when the magnitude of the vessel's field is too large for the onboard system to compensate the vessel must undergo magnetic treatment.

Significant magnetic effects may arise in any object containing ferro-magnetic material. The strength of the magnetic field is determined by the shape and composition of the object, and the ambient magnetic field. For a ship or submarine, the field is complex and changes with heading and location. The measured field is three dimensional in nature and is expressed in terms of three mutually independent orthogonal components; being the longitudinal, athwartships and vertical fields. The total field is the vector sum of these components. Magnetic signature minimisation can be achieved by magnetic treatment (or deperming) and degaussing.

HMAS Melbourne is now enroute to the Middle East as part of Operation SLIPPER.