I spent a summer cleaning hulls down in Discovery Bay, CA (freshwater). I just used my regular set up.

If you are staying shallow, as you do when cleaning hulls, a hookah system that provides you with surface supplied air allows you to stay down much longer than an air tank. Even though you are shallow, because you are working, you can burn through the air in a tank relatively quickly.

The initial cost of a hookah system will be greater than renting or buying a tank, so it depends how much and how often you are going to clean hulls.

Hookah systems are often used by working divers who are spending a lot of time working at a shallow depth. For example, golf ball divers use them. Eventually, they pay for themselves, but you can rent a lot of tanks for the cost of a hookah system.

Be careful. Hull scraping can be dangerous work. Marinas tend to have dirty, murky water and people tend to toss fish scraps and other garbage over, making marinas hangouts for the notoriously aggressive, man-eating bullshark. At least that is the case down on the Texas coast. You could not pay me to dive a marina on the Texas coast.

Also, do not use a brightly colored or silver colored scraper. Some fish, like barracudas, have been known to be attracted to the back and forth scraping motion of a silver scraper and bite the scraper (including the diver's hand.) While barracuda attacks on divers are very rare, in a marina, the low visibility can make for honest mistakes.

If the water is dirty or polluted, I recommend a drysuit and full face mask.

As a sailor, and a diver, I vote for pulling the hull out if you can. A fresh coat of bottom coat will pay for the hassle and cost. No bottomcoat and the marine life will be back in a matter of months, if not sooner...

If you have to scrape the hull, regular gear is much preferred to snorkel, and a hookah is the best option.

Echo the marine life warning...my worst fish attack was a bunch of Sgt. Major fish while cleaning a boat in the Caymans.

Plus you'll get for a bit of ribbing from friends at the bar if you come in complaining of fish bites while cleaning bottoms.....

I use a hookah system with a built in powered hull scrapper that I built from some military surplus and a couple of old Briggs & Strattan paint compressors. For backup, I have my homemade rebreather/scrubber system that employes coffee canisters filled with peat moss.

The whole thing cost me less than $200. Unfortunately, the committee at the Lake Elephant Butte Yacht Club refused to let me set up shop on their premises, so I did not get to try it out on a commercial basis.