My Volvo Penta 2004 D-2 55 pushes my Bavaria 41 at 7 knts at 1800 RPM with existing 3 bladed Aluminum prop. I can push RPMs to 2200 and get 8 knts. Above that either hub or clutch begins to slip. The 55 specs suggest it should be maxing out at 3500 RPM, so I am not close. Even before slipping appeared, I could only get 2400 RPM max. The reason for the slipping is one question I would like to know. Prop re hubbed does not solve slipping problem. Boat runs fine if I don't push RPMs so I could leave it alone and run at 1800-2000 RPM with great fuel usage at 7 knts. I want to know if I need a lesser pitched prop to allow engine RPMs to increase. What is the 3 bladed propeller match (diameter and pitch) for this boat and engine sizing?? Anyone with experience on this question, both the prop match and slippage, which may be the transmission clutch. Any help?