Bill, you could be correct about the capacitance and inductance theory..
But there is my take on things.
Lightning is a transient event.
When we protect electronics from transient currents, one of the methods used is to INCREASE the capacitance on circuit nodes. Capacitance will limit voltage transients caused by current transients. For example, if I inject some amount of transient current into a circuit node (such as the DC input), it will cause a voltage transient depending on the impedance. If the impedance is high, the voltage transient on the node can then breakdown semiconductor devices causing damage. However, if the capacitance on the node is increased, the voltage transient is reduced - which is a good thing if you don't want damage. You generally cant just add capacitance to any node as this will affect the way the rest of the circuit works - but additional capacitance is a good thing from a circuit lightning protection standpoint.
Also, if I charge up a capacitor - it doesn't just arbitrarily discharge.. It will simply remain charged until some impedance discharges it. My opinion is that any sort of capacitance on a boat is going to be BETTER for reducing lightning damage as capacitance will reduce voltage transient amplitudes.
Regarding the inductor or choke between the mast mast and the keel (if i understand the idea correctly) - I think this is the wrong thing to do.
While a capacitor will limit voltage from a current transient, an inductor will do just the opposite - it will create voltage transients from a current transient (v = L * rate of current change).
Not considering electronics, what lightning protection on a a boat is trying to do is prevent side flashing inside the boat. The heat generated by an ionized path is huge compared to the heat generated by the same current in for example a 4 gauge wire. Ionized current going through a fiber glass hull - also obviously not a good idea.
So what will happen if you have an inductor between the mast and the keel? If the mast receives a strike, you now have a big transient current in the mast. When this current "goes through" the inductor between the mast and the keel, a large transient voltage is developed at the mast. This is a bad thing as the transient voltage on the mast is possibly going to arc using ionized air over to the nearest water surface - ie, generate a damaging side flash.
I think what is a much better idea is to minimize the inductance between the mast and the keel as this also minimizes the chance for a side flash. Note that this only effective in salt water as the keel also needs to look like a low impedance path to discharge in the water - which is apparently sort of true if the keel is large enough and the water salty enough. If the keel doesnt look like a low impedance (such as in fresh water), you can still get a large voltage transient on the mast - and the possibility of an ionized air side flash.
Another point about inductance - you will hear about attempts to protect a boat by just attaching a wire to a shroud or chainplate. This also is likely not adequate because the shroud forms a fairly large inductor back to the mast. As discussed, the inductor will allow large transient voltages due to transient currents. So trying to "ground" at a chain plate could still allow the mast voltage to get very high - and then side flash - which of course is bad.
I also just don't see any benefit to a isolated / insulated mast from lightning. Electrolysis is another separate issue... but I don't think it makes much difference to lightning. However, I don't think an insulate mast hurts anything and that a spark gap can be used in the transfer of energy to ground.
