PA you're assuming that your wife's mind CAN be changed. More typically you give up the dream or get a divorce. A cheap 40' boat is still going to cost you over $50k no matter how you slice it, and no matter how many nights and weekends you abandon the wife to work on it. Most women want a nest, safety, and security, and a boat just ain't it.
If you can get her to enjoy daysailing, if you can upgrade that to enjoy cruising, if you can convince her the finances aren't lunacy, I'd say you still have a five year project swinging her opinion around, half of that minimum.
If the finances alone don't cause a divorce, and she can tolerate "dad's hobby working on the boat"...you might get her to see the rest. But the odds are probably about 100:1 against you converting her. And that's optimistic.