My Cal 34 has a prop that measures 16”, pitch unknown. Engine is yanmar 3GM30F. On a recent cruise I ran 2500 rpm and only made 4.5 knots in still water. Admittedly when I hauled it today there’s lots of barnacles on hull and prop. I’m thinking the prop is undersized. There’s a chart on Marine Diesel Direct that recommends for this engine and transmission either 2 blade 17x12 or 3 blade 17x11. Advice or recommendations?