Thanks Chuck,
I have a pretty good handle on electrical hazards except for your distinction between fresh & salt. Isn't saltwater a better conductor? Being in the water you will be grounded. If the boat is wired improperly there is a chance of current flow from any bonded item (zincs, steel hull, running gear) to ground. If a diver (encased in wet neoprene) touches one of these "hot" surfaces the likelyhood of electric shock should be minimal as current will follow the path of least resistance. I would expect that to be the surrounding water not the wet neoprene.
I do see the risk of coming in contact with defective wiring or fixtures while exiting the water.
If you have one foot in the water and grab an exposed hot wire you are definitely in trouble!!
So, there is my "textbook" understanding. What is it like in the real world?
As to the marketing side. I have seen people placing doorhangers advertising services on boats in a marina down in Santa Monica. I expect that this is quite common. I think that offering something special to first time customers and showing them when you perform the service that you provide a superior service. The question would be: what to offer that will set me apart from the others (in a good way) ??
As to the Brownie's unit. It uses a tank secured to a kayak. No noise. I thought the kayak may make a good staging point for tools etc.
If I can clean a 40' boat hull & gear in two hours and charge $150 I would need to average about 40 boats a month to cover supplies, insurance, office overhead(minimal), marketing and make a reasonable wage. Maybe even throw a little into the cruising kitty.
I am currently living in NW Arizona. Not a huge amount of potential business here. Nor is the diving & sailing that great.

We do have 3 lakes in the region with marinas that are anywhere from 20 minutes to 2 hours drive from here. I have my home for sale and when it finally sells I am headed for the ocean. Most likely either Southern California or Seattle area. Anybody want to buy a house in AZ??
I am thinking that I may try to find someone who is offering these services in my area and offer to work for free one day a week to learn the ropes.