Following on from a couple of threads on the "should we - shouldn't we" anti-foul our hulls I would add my recent experiences.
My boat has been berthed in Portsmouth Harbour for 4 months, it was waxed before it went in and subsequently dived on three times and beached (not literally) for a brush/spong a couple times and after a three week break in tlc it was covered in weed and 4mm barnacles. Speed and fuel usage had both suffered dramatically.
As it is going to have a continued hard summer I took it out, cleaned it right back, primed, undercoated and anti-fouled using Blakes Hard Racing (recommended by a great many racers in our area) as I wanted to be able to burnish it smooth.
Being an impatient b*****d I launched the boat without a burnish for a session last weekend and have immediately got 99% of the performance back INCLUDING the top speed, thus exposing the "it will knock 10% off your speed" myth. Fuel consumption was also back within it's usual parameters.
I have now burnished it. It is about as smooth as a painted surface will ever be without taking it off (I have had a LOT of practice burnishing racing yachts!) and have seen the performance come back to being identical to pre-treatment and pre-weed!
Obviously it now needs to stay in the water (currently 23.5degC in the Marina!) for a while to see the effectiveness of the treatment but assuming that it stops growth then I can safely say that I can see no reason whatsoever (environmental issues notwithstanding!) NOT to antifoul a rib if it will be spending prolonged time in the water. (It also looks sexy as f**k as I did it in navy to go with the white and navy theme of the topsides!!!!)