This paper shows a practical application of genetic algorithms (GAs) for compensating the local magnetic perturbation produced by a ship, while moving in the earth's magnetic field. The compensation is achieved by modifying the number of turns and the current magnitude across the so-called degaussing coils distributed along the ship. A GA scheme for automatic optimisation of these parameters is used. A new objective-function strategy, called a boundary method, is proposed. It is shown that the convergence of the GA is greatly improved when the new objective function is used. Different selection mechanisms, objective function strategies, and scaled methods are revised in this paper. The results show that GAs can be efficiently used to reduce drastically the magnetic field levels of real practical ships. © 2005 Wiley Periodicals, Inc. Microwave Opt Technol Lett 47: 281–287, 2005; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.21147