The only restriction for the rails would be that it fits within the maximum width as allowed by the class, 2.3 meters. The class rules can be found at www.usaca.info. Many of the newer boats have canted hulls causing the boat to be wider at the bottom of the hull than the top. To make up for this width loss rails can be added. Many times the manufacturer offers this as an option. If the boat still measures within the 2.3 meters there is no penalty, if not the boat is not an A-cat.