This rule promoted the use of fin keels and blade rudders. The caudal peduncle is slightly compressed with weak lateral keels. The caudal peduncle is expanded laterally into strong keels. Caudal peduncle shows strong double keels on each side. The sides of the caudal peduncle are expanded into prominent lateral keels. Bilge keels are passive stability systems. She rolled badly until fitted with bilge keels. The dorsal scales are smooth and without keels. Four bilge keels were fitted to improve stability. Both completed ships rolled badly until fitted with bilge keels. The caudal peduncle is flattened from side-to-side and lacks keels or notches. The caudal peduncle has a couple of less distinct keels. It is smooth and has neither dorsal or lateral keels (ridges). "Macon" had a structured duraluminum hull with three interior keels. Models have been built with folding centerboards, wing keels and fin keels.