i keep mine in for 11 months a year only really pulling it up if i go off on hols's or if extreme bad weather is forecast in the winter
i thought long and hard about antifoulling the 6.8 ribcraft i have....but after pricing it up and because i have the use of a crane i fitted lifting eyes for it and lift it out every 5-6 weeks and bleach it.
cost of eyes were £65 cost of the antifoulling and primer over £120 and then the elbow grease to sand off the hull ,loosing the shine to get the paint to stick...
i loose about 11-12 knots of top end after a month of growth..
another con' re antifouling is if you sell the rib at a later date...some people are suspicious of the covering of the hull...however on the plus side you can fair up the hull with isopon and then paint rather than using gelcoat filler and lots of wet and dry.
if you were to antifoul ,once the hull is sanded back ..make sure you degrease the hull as apparently wax from the moulding can still be present which throws the primer off....