I highly recommend the Womens Sailing Organization Women-Only Diesel Workshop. I took it a couple years ago, and my confidence working on my own diesel sky-rocketed. They're holding another one in Massachusetts this February over a weekend.
Before anyone flames on about womens-only-anything, I have a long career racing cars and building my own gasoline engines. However, the shared experience of a group of about 15 women learning together about diesel engines was priceless, and I am not normally a big fan of women-only-anything. (I mean, come on! How are we ever to meet interesting men if we engage in women-only activities?
The big benefit of the workshop was that no one was afraid to ask a question, no matter how "dumb" it might be, everyone shared knowledge and experiences freely, and everyone had a chance to get their hands dirty actually working on the motors. That is not something I find available in a mixed-breed workshop.
I can't recommend the Mack Boring Womens-Only class highly enough, if confidence in working on the mechanical aspect of the boat is your goal.
Now, can anyone PLEASE recommend a similar way of learning about the electrickery? I have a definite mental block and scaredy-kat mentality when it comes to things that spark and go boom, or worse smolder and burn when you're not looking....