I have read articles by 'experts' claiming that dissipators don't work. I don't recall the author of how he reached that conclusion.
I also recently read that a one foot square plate should be attached to the underwater surface and grounded to the engine and only the engine. Bonding the metal fittings together, the article said, only increases the oportunity for lightning to blow a hole in the boat.
I'll see if I can find some research on the topic. I'd like to know.