I have owned my boat for nineteen of its twenty-one years. My Yanmar 2QM15 has been a faithful friend through all that time. It is well cared for, has between 3,000 and 4,000 hours, and had a top-end rebuild last year. The mechanics confirmed that it was in generally very good condition. After reassembly, (we did not change rings or cylinder liners), there was some blow-by evident when we ran it with the oil fill cap off, but the mechanic felt this was not a big problem. I have two battery banks of 220 amp hours each, each bank consisting of two Trojan T105 six volt golf car batteries, run in series. My question relates to my choices of alternator. In 1987 I replaced the stock 35 amp Hitachi with a 55 amp Hitachi. When I started serious cruising in 1991, I added solar panels to help with charging, but found my system inadequate. Some years later I replaced the Hitachi with an Ample Power hi-output alternator.I use a "smart" regulator. The alternator will put out about 100 amps at 2000 RPM's (engine - the alternator RPM's are about double) when the engine is hot. Cold, it puts out more. However, when it was putting out its full capacity (I have a 1700 watt inverter from which I can run a two gallon water heater with a 1500 watt element), the engine was unable to turn more than about 2400 out of its normal 3000 RPM's. At that speed it was obviously laboring, although at 2000 it seemed happier. Eventually, I changed pulleys to diminish the alternator output by about 20%, but I am still concerned. An interesting symptom: Even with the reduced output, if the alternator is putting out to capacity, when the engine is in gear, oil pressure will drop noticeably when the engine gets up to about 2100 RPM. Out of gear, but with the alternator putting out the same way, there is NO drop in the oil pressure. This drop is not associated with a slowing of the engine...it occurs as the engine's revs are increased! To me, that is a sign that, for whatever reason, the engine doesn't like the alternator load. I am using one belt, by the way, and it doesn't slip. So, I think I have several options. The easiest, of course, is to revert to the Hitachi 55. But, I would like to get the charging ability of the big alternator, particularly if I am running the inverter. (Incidentally, my solar array now is about 370 watts, so I don't have to sit at anchor running the engine for charging purposes, under normal circumstances). So, my thought is to stay with the big alternator, put back the original pulley in order to restore its FULL output, and then operate in one of the following three modes:first mode...out of gear, charging both banks at a high rate. I figure the load to be 2 to 4 horsepower (calculating losses to heat and friction at 50%) at 2000 RPM. Second mode: in gear, under way, charging only one bank at a time. Unless very deeply discharched, the acceptance rate of a single bank should limit output to about 60 amps....no problem of the oil pressure dropping. Third mode....if, for whatever reason, I need full output underway (inverter load or charging both banks from a state of moderate to high discharge), I would not run the motor in excess of 2000 RPM's. The goal of all this would be to eliminate overloading the engine with the simultaneous loads of propulsion and max output from the alternator. Obviously, the little Yanmar is a bit undersized for a 33 foot boat and all the other tasks! So, it would basically work either for propulsion or as a generator. What do you think? Am I ruining the engine? Will the big alternator sufficiently load up the little motor when it is out of gear? Why does the oil pressure drop? Should I just go back to the Hitachi 55? (the easy, but less desirable answer!) Do not worry about the complications of my proposed procedure...I am the only operator, so the different procedures would be followed. Thanks for taking the time to read all this...and I will be eager for your opinion. I really want to take good care of the engine...maybe it will give me another twenty years! Regards, Tim