Yanmar 4JH3-TE: What are the long-term effects of being overpropped?

Have about 350 hrs. Seems to run good. Per Yanmar, this engine has a max. rpms under load of 3800. I can only reach about 3700-3750 according to the boat tach. under load. This is the best that I have ever done. Comparison with a hand-held photo laser tach at 3800 rpms in neutral, the boat tach is reading about 150 rpms higher than the hand held. Therefore, I need to gain at least 200 rpms in order to reach 3800 max rpms under load. I usually run the engine (in small power boat) in the range of 2000-2500 and try to run at least 5 min. or so at 3000 rpm whenever I am out. I know that I am over-propped and should probably for next season have the pitch reduced an inch or so to gain 200+rpms or swap the prop out with another. Question: What damage or long-term effects does being over propped have on the engine given how I currently operate it? Just how critical is it to achieve max rpms under load? I never get any black smoke just white smoke at times at idle. Please advise. Thanks, Jim

Based on discussions with others (prop shops, Mack Boring, etc.) and my own research on this question I have determined that the long-term effects of being overpropped will be a (unnecessary) strain on the engine throughout the rpm range. This is not good. To remedy this problem, I had the pitch on my prop reduced by 1.25" by a local prop shop. This should (hopefully) now allow me to reach max rpms of 3800 under load which I previously have not been able to do. I will confirm this once my boat is launched next Spring 2011. Hope this helps others who have interest in this issue.

Jim