Having managed a marina in the past and lived on a boat for years (though in the NE US) barnacles love fiberglass, wood, and metal equally. How many you get depends on how much the hull moves over a period of time - it's sitting where they hit hardest. I used to chuckle at the folks that would refuse to put copper bottom paint (I always used green as the copper content was higher - and cayenne) on their hulls because they were only going to be out for a couple of days here and there. They'd go out for a couple of weekends, anchor and be scraping when they came back. The paint would last me about a year with two coats, but did nothing to keep them off props, shafts, zincs and anything else not painted. Warmer water, more barnacles. More frequent movement in the water, less barnacles.