Protection of naval systems against electromagnetic effects due to lightning

This study investigates possible lightning threats to naval crafts, especially those sailing in the shallow waters of tropical oceans where thunderstorms prevail throughout the year and Far-East Asian region where dangerous positive lightning is a signiflcant characteristic in winter thunderstorms. It is empathized that sea water acts as nearly a perfect conductor thus lightning electromagnetic transients propagate over the sea with almost zero attenuation of amplitude and high frequency components intact. The ratio between the peak electric flelds at 5km from the lightning channel, after flelds propagate over dry soil and over sea water is 0.75. The ratio between the peak electric fleld derivatives under the same conditions is 0.1. Such small ratios are observed in the magnetic flelds and their time derivatives as well. Apart from the conductivity, the topological irregularities of the plane over which propagation takes place also contribute to further attenuation of flelds and their time derivatives. This makes marine naval systems more vulnerable to lightning induced efiects than their ground-based counterparts. The paper discusses in detail the lapses of existing naval standards in the defense of electrical and electronic systems against both direct lightning currents and induced efiects of nearby lightning. Consequently we propose the development of a dedicated standard for the lightning protection of naval systems, with the inclusion of several signiflcant recommendations specifled in this paper.