Spark Gap (surge or transient protectors) are most often utilized in an attempt to provide an AC, RF, and/or Lightning
ground connection; whilst maintaining Galvanic (DC) Isolation (to prevent electrolytic corrosion
of immersed metals) in bonding conductors. Often the Spark Gap is bridged with ceramic capacitors.
Many “home-made” Spark Gap devices are probably ineffective, and potentially dangerous.
The main downconductor (mast to water) is probably the last place I would install a spark gap.
Metal boats are frequently struck (by lightning), but the high conductivity of the large quantities of metal, with hundreds of square feet of hull
in direct contact with the water
, causes rapid dissipation of the electrical
charge. - so significant damage or personal injury are relatively rare.