As I was told back in the day, when Yamaha entered the outboard market they started rating them at the prop. Evan rude had to switch for some reason so that they could compare the motors I guess. Pretty sure the 83 is at the crank but I'm not sure because that's right about the time that things started changing. As far as the 30 and 35 goes like the man said above it will probably be very similar when driving the boat.