Brian posted:" ...Many of these (displacement) boats could be run more efficiently at a lower RPM by using larger diameter props. But you must remember that by doing this you will lose the ability to utilize all the power available from the engine. Comments: (a) I've often heard this, but have wondered if the extra loading at the now lower cruising RPM results in equivalently long engine life. In other words, are you trading off low RPM for higher load and gaining or losing engine life? (b) Assuming its good and economical, you can also achieve the higher loading (reducing top RPM) by increasing pitch, adding props with more blades, and or by cupping blades. These strategies are especially useful if diameter is limited by underwater configuration. I had some blades on a prior boat moderately cupped and it reduced my top RPM a few hundred revolutions. I did not care since I never ran anywhere near top RPM anyway. Rob Brueckner 1972 Hatteras Yachtfisherman