JR says... in answer to RYYC queries..... 2-bladed and 3-bladed fixed props do not perform equally, and so this inequality would in itself favour some boats  over others and thus the one-design status is compromised at this level  alone.... The Contessa 32s take a more general view that no two boats are  exactly alike anyway, so all propellers are treated equally, but there was a  lot of discussion over it before this sensible approach was adopted.   Classes evolve as equipment improves.