I tend to find a light layer of green growth... something that can be removed with just a hand passing over it or a rag. No brush required. During the summer months, this growth tends to be heavier on the south (port) side of the boat, and right at the water line.

Now my speedo paddles are another story. I don't quite get it, but little crusty worms seem to want to nest in there, and within just 2 weeks of a cleaning, I will find such critters lodged in there.

The sides of the docks, on the other hand, are a "zoo" by comparison... and rather dangerous to casually brush up against. I have seen the marina staff knocking off the heaviest growth in some slips. (is it a "plume" when it just falls straight to the bottom?)

I find that a one month schedule works just fine.

The boat I race on also has a one month schedule, but the skipper also calls the diver before races.