The jury is still out on the actual science of the lightning
strike--but I made my living fitting lightning protection to electrical
outside plant and I can tell you what works and what is a waste of time. Forget about "experiments" where high voltage generators discharge into buckets of water etc. They bear little if any resemblance to a lightning strike, a moderate one which has the power dissipation of the order of 10 to the power of 12 watts.
There is no practical size of lightning conductor able to conduct this magnitude of discharge to earth during the short few milliseconds of a lightning discharge without being vaporised--so all conductors, even those which do conduct significant portions of an initial and subsequent discharge to earth, have "bled" most of the charge before the air became sufficiently ionised to allow the balance of the discharge and any subsequent or consequent discharges to reach earth through the conductor itself. If you think of the steel-melting capability of a reasonably powerful arc
welder as being about ten thousand watts, you get the picture as to the metal-melting capability of the spark from a moderate lightning discharge.
It is possible for a yacht to be at sea with no discharge protection and not be struck, and the reason forn this is simply that they were not the point on the "capacitor plates" where the "dielectric" was weakest. Because the strength of this dielecttric is not a constant, and niether is the conductivity of the earth (the sea is pretty consistant though), variable factors something most of the experiments do not take into account, sailing without lightning protection or feel-good protection based on wishful thinking or tiny-tots sufrface-skimming experiments is like buying
lottery tickets where the prize is severe burns, death, and damage which might extend to loss of the vessel and crew.
Now--because the turbulent air does not have constant electrical
properties, there are rising and falling columns of air, air at different moisture contents and temperatures, and the potential lightning-forming charges in the air are not evenly distributed and are rising and falling in strength all of the time, tiny-tots experiments are a complete wank.
Some of the best labopratories have studied this phenomena, testing only one facet of the discharge sequence at a time because that is all that can be tested unless one goes outside and studies the real thing from satellite
photographs etc, and actual discharge sequences. Sometimes these are artificially initiated.
None of the outside plant to which I had fitted simple dissipative protection was ever seriously damaged by lightning after the protection was fitted, although unprotected plant was an expensive damage bill waiting for presentation.
People think of the earth and the charged clouds and moisture and dust particles in the atmosphere as though they were separate conductors, whereas it might be better to think of them as plates of a leaky and badly out of balance mega-capacitor, with the turbulent and irregularly insulative/conductive lower atmosphere as its dielectric. Make sense so far?
OK--some simple facts.
You do not have to use copper--going up a guage or two in aluminium works just as well and will not cause corrosion
if you wish to keep your electrode in the water while you are absent from the vessel. The last one I used was a plate of marine
aluminium alloy, about 6 mm I think, and it swung up and down on a pantograph between the hulls. It dropped into the water and could be used while sailing because the wires which suspended it also acted as lateral braces. It protruded below the hulls by about 300mm--but it would have made little difference if it had not. It could be hauled up out of the water by a lanyard and secured. To this was fitted an aluminium strap which I got from a power distribution company--which led to the base of the mast. The mast itself then became part of the dissipation path--and at the top of the mast was a single
rod sharpened to a point. Before this I had used the brush collectors--but the rod was simpler and had less windage.
Now--when there is the potential for a strike several factors have to be present. The air has to be ionised for the initial strike to occur--the air has to be moist to be able to become ionised easily, and the air has to be highly charged in order to create the electron flow and potential differences throughout the air mass between earth and sky for subsequential and consequential discharges.
Enter the earthed rod.
This plus the boat and her rigging
act as a huge discharge sink for electrons, which stream from the surrounding charged air on to rigging
and lightning rod. Sometiomes the discharge is so intense tht it becomes visible as streamers of white or blue, or sometimes blue flickers, the St Elmo's fire old salts used to sea on the wet rigging of sailing ships on the wool and tea routes through tropic seas and cold Altantic storm waters alike.
If you can bleed enough charge from the air surrounding the top of your vessel, you greatly decrease the likelihood of an initial strike. Even if you are struck--very unlikely, so much of the discharge will already have taken place that your damage may be significantly lessened, but I am only theorising here because I have never seen a strike of any kind on properly protected plant.
OK--the initial strike will ALWAYS occur where the dielectric strength of the atmosphere is at its weakness, but once there has been a change to the balance caused by the initial strike, the whole system changes and many other charged particles and areas of high charge density elsewhere in the atmosphere will opportunistically discharge into the same discharge path--greatly multiplying the effect of the initial strike.
Best you do not encourage that initial strike--because if that is what you think your lightning conductor is for--lotsa luck!!
A building is set up with several conductors, usually at least four, one going down each wall. The boat can be rigged the same way using the shrouds, and I have always done this. They do not have to be connected at the base--they collect and discharge via the top of the mast just fine.