Yeah, On your cat where you have an acre of roof for solar I would agree with you. On a J boat where would you put that many panels? Almost impossible; unless of course you add the jungle gym and use solars for awning / bimini material.

And of course you're talking about sunny days. Sometimes one might go a day or two or god forbid three days with very little Sun. Then you're into running (in your case) the generator, or in the case of a J (I doubt much under 40') they would have to run the main engine or else find a place and a cost for putting a small generator.

Go Slow
Sail Far
Stay Long