Older, longer P15, 16 and 18 rudders (37 inches tall) vs Shorter P18-2 and 19 square bottom rudders (35 inches tall). The smaller rudder in the photo has had some of it's lower end removed (probably dropped down while trailering). The Two and the 19 had smooth hulls and centerboards, so didn't need as much rudder surface area. Look elsewhere in this album for a picture of the yet-newer rounded-tip 19 rudders. The rounded ones came on the P19 MX, and resolved some steering issues with the MX's decksweeper-style jib.