My ballast, as an example, is completely encapsulated and not grounded to anything. Water from a hole in the hull down at the ballast does not get into the bilge anyway. I have proven this:-) All my metal parts are bonded well with what looks like #6 stranded copper back to a sintered plate by the engine. I think the bonding idea makes a lot of sense (if anything does in this lightning topic) in that if your boat and the surrounding sea all have similar electrical potential, lightning has less reason to be attracted to your mast any more than to the surrounding area as the shortest route to ground. Under those parameters, lightning has almost the same chance of hitting 50' from your boat as it does striking the boat. That is what the grounding system does more than attracting lightning to a safer route through your boat. Lightning is trying to get to GROUND, not the water. If the boat looks like the rest of the water, it has less reason to target the boat. The mast is a better conductor than air so the closer it can be to the potential of the sea, the better. Anyway, although counter intuitive, that's the way I've heard the grounding idea explained. If you have contradictory theories about this, would like to hear them. Once lightning actually makes a direct hit, all bets are off and you're just lucky if it doesn't travel in a direction which burns a big hole in the fg.
In theory this all sounds well and good but the existing data does not really support it other than for a very small edge to well bonded boats vs. un-bonded.
Beyond that people often lack the electrical common sense to realize that most every spar out there, with a VHF whip, is already at ground potential.
All one has to do is follow the shield of the VHF cable back to the VHF then to the ships ground which is engine/water/Earth. Take an OHM meter and put it on your mast now put it on the engine block or battery neg and you will have continuity. Why? Because the VHF shield is almost always bonded to the mast bracket which is rarely isolated from the spar. Mine is but this is a custom mount I made on my own. Most all masts are already at Earth potential whether bonded with heavy wire or not. Most boat owners simply don't understand their VHF whip is already putting their spar at Earth potential.. The heavy wire does not change the Earth potential beyond the small VHF wire but it can help to take the brunt of the strike to Earth which the small VHF wire does a horrible job at......
Just last week I was just talking with another member here who's boat was hit while on the hard. This makes it fully isolated from the Earth as in no connection at all. The lightning came down the spar into the keel and physically jumped the 12" air gap between his keel and the asphalt.... You don't even need Earth potential to be hit. However if your boats bonding wires are large enough that they can act as a "pass through" then you may just suffer less damage......
The heavy bonding wire is intended to minimize damage not prevent or minimize a strike. This is the area where I do see a large difference in damage results. Well bonded boats with heavy grounds suffer less damage, but they still get hit.