Crazy Woman Boat Driver
Join Date: Apr 2004
Location: Heading south down the US east coast to the Bahamas
Thanked 17 Times in 14 Posts
Rep Power: 14
Operating a diesel engine with no load or constant low RPM is bad. I believe what happens is called wetting in the cylinders. As to your question of a high output alternator that depends. How high and what size engine you have? Most small engines under 36 horsepower the biggest alternator one can put on without major modifications is 100amps. Over that amperage, one needs to put on a double pulley system or two alternators opposite of each other. One will lose about 3 Horsepower on the engine for high output alternators. 3 horsepower is not a big load on the engine.
Having said all that, charging the batteries using only the engine can be done. One has to remember that max output on a alternator is not achieved until around 80-90% of engine RPM. So running at that RPM is better for the engine than idle or low RPM. Second, I would recommend run your engine under full load (motorsail) for a time afterward to clear out any wetting process that takes place. If most of your hours on the engine is charging the batteries I would find another way to do that i.e.; generator, solar panels.
Catalina 445, Hull #90