My brother's boat, kept in the same marina was covered with growth in a year and a half.
So you're saying that nobody had a look at your brother's boat below the waterline for a year and half?
I don't care where your boat lives or what the fouling conditions are- that's playing with fire. You at least want to check your zincs a couple times a year. Not to mention cleaning the running gear, even if the hull doesn't need it. Wow.