anti-ventilation plate

I need information for the anti-ventilation plate.I build a 25 feet hard chine 7 degree transom boat with 50 hp inboard. I had no information about anti ventilation plates when building. My rudders end is 10 cm out of transom. I see air bubbles behind the boat and decreased the pitch of the propeller for probable cavitation effect but still air bubbles exists and I see a increase in rpm but very little effect on speed improvement so I wonder if this is because of missing anti ventilation plate. And does this effect the trust or is the anti ventilation plate just only effective when monuevering.