We took a diesel engine class last weekend. It was only a one day class so for the most part it was an introduction to diesel engines and maintenance. We'll definitely be taking a more extensive hands on class when it's offered later this year. The main thing we took out of this class is that we've been babying our motor. Every diesel has a continuous RPM and horsepower that it's rated at. For us this is 30hp @ 2600 RPM. If you don't run ever run it that high you run the risk of getting soot buildup inside the motor. Normally when we've been motoring I'll put it at 1900-2000 RPM and get 5.5-6 knots out of it. I kind of felt that was running it hard, but I guess not. So we took the boat out and I incrementally moved the throttle up to the stops, where the motor hit 2600 RPM, we made hull speed, and nothing blew up.
We've actually sailed the boat at 7.5 knots, so it's not a speed record for us or anything but it's nice to know we can motor at 7 and not suffer and adverse consequences!