I don't know of a city ordinance that addresses that, so it may be a Home Owner's Association rule.
Click here for city ordinances about your property:
http://www.louisvilleky.gov/ipl/Prop...ter156.htm#052
I would not go off the deep end over the issue - I would talk with the neighbor and discuss the issue and find out what her real problem is with your boat in the driveway. You're better off to try and compromise with the person who has the issue than to fight it. It's the whole catch more flies with honey kind of deal. I'm sure if you look around the neighbor's yard, you probably could find some infractions that you could report as well...but nothing good comes from playing that game. If building a fence gets her off your back, that would be far cheaper than building a garage or paying a storage building fee.
I live in an area of Louisville that is under HOA regulations. I am on good terms with my neighbors. They don't care what I do, and I don't care what they do - it's just a friendly mutual understanding. I've had multiple boats in the back yard in the grass for months at a time, and no one has said anything. There are also others in the neighborhood that have blatant violations, but aren't made into a big deal by surrounding neighbors so they get away with it.
I would recommend that you try and get involved with the local HOA. So many people have little interest in it that you can make major changes that go unnoticed, like repealing the boat in your driveway rule, or at least amending it. Junky little uncovered eyesore jon boats and the monster cabin cruisers that block out the sun are the reason for the rule - I wouldn't want to see those in the neighborhood, but have no problem with covered 18 - 22 ft boats sitting in the drive.
HOAs are all about maintaining the integrity of the neighborhood and keeping property values up. They are a safety net to keep the trash out, or at least suppress them if they get in. They do far more than you probably realize, and are a good thing. My HOA membership fee of $25 per year keeps the street lights on at night, and the roads plowed during the winter snow storms. When I bought my home, HOA membership was a requirement, and I considered that a bonus and added value. It's a valuable tool, if you choose to embrace it and play by the rules.