I believe that even when the electricity is created by 100% coal, it is still cleaner to charge an electric car with that electricity than to burn a gas engine. However, electricity is rarely generated by 100% coal. In Ontario, we have (or are about) shut down all of our coal plants.
As for boats, I think that if Tesla and others can make a compelling mass market electric car, boats will follow soon. Or at least, they can run on clean biofuel.
Wait, I just had a brainstorm: For a dedicated ski lake, I wonder how much a battery would weigh and cost to power an 8 pass set? Imagine if you arrived at the lake, with your ski and a briefcase sized battery, got on the boat, plugged it in and skied. After your set, you yank the battery and recharge it while getting ready for the next set. The boat could be kept very light with just a small backup battery and motor. It would probably weigh less than a current ski boat.
Hmmm... A 240volt outlet, running at 80 amps (I have one in my garage) for 1 hour could completely charge a 19kwh battery. That can drive a Tesla 100km. Could that power an 8 pass set?. That's about $2.50 in electricity. Optimistically, at $180/kwh, 20kwh battery would cost $3600. I have no idea what a battery like that would weigh. My initial calculation is 80kg with a power density of 250 watt-hours/kg. That could be a problem.