We keep Friday Girl in Brundall, where the water is brackish at worst and possibly nearly freshwater. Hence we don't bother with antifouling are all. She gets either a Summer Scrub (calm down, JanetAnne) or, on alternate years, is taken out for a few months to dry out on the hard. We do find a thin coating of slime but this quickly washes off. I've personally not noticed any degradation in performance as a result of not bothering about water level weed growth, other than to take a brush to her occasionally.