I never seen anyone use floating compressors maybe there is a reason? If not then I'll have to find one. Compressor sounds like a good idea but I wanted an excuse to be certified.
I have never seen a hull cleaner using a floating hookah. I suspect the reason is that they are expensive, cumbersome and heavy, not to mention require fuel. The gear you use will depend on where you are working. Here in the East Bay Area, we have no mooring fields. That means all hull cleaning is performed at the dock. That means free shore power. Why pay for air or fuel when an electric hookah is unlimited free air? Not to mention lightweight, compact and inexpensive to buy.
I personally work out of a boat but still use an electric hookah. If you plan to service boats at anchor or on a mooring, of course you will need a gas-powered hookah (or an electric, run off a gas-powered generator.) But you should get certified regardless (he said, acknowledging that he has never been certified

) for the safety aspects, if nothing else. Plus, you never know when you might need to use bottled air for a job and, of course, you need SCUBA certification to get refills (but not to SCUBA dive).