NC-PHRF sent out the new 2011 yearbook this month.  They are now allowing a whopping 12 sec/mile for a 2-blade vs. folding prop.   On my Pearson 30 (3cyl 20 hp Beta Marine 722 engine), the exposed prop could be a two-blade fixed vertically behind the keel turbulence when racing, and I'm guessing that's not that much more drag than my very effective Martec 14D, 11P.  I wonder what the smallest diameter two-blade prop would be that would move the boat effectively?  Is this worth considering?  Thanks.