There is no tax benefit for transferring ownership of your boat to your ex-wife as part of the divorce settlement.
Did you actually transfer ownership of the boat to your ex-wife, and then she, as the new owner, sold it? Or did you remain the owner and your ex-wife arranged a sale from you to the purchaser? You said that she paid a title transfer fee. Was that for transferring the title from you to her, or for transferring the title to the purchaser?
If you transferred title to the boat to your ex-wife as part of the divorce settlement, there is no tax effect for you at all. You do not report the transfer on your tax return. But if you still held title to the boat until it was sold, then you were the seller. If you sold it for more than you paid for it, you have to report the sale on your tax return and pay tax on the profit. (If you transferred title to your ex-wife and she was the seller, then she has to report the sale and pay tax on the profit, but that's not your concern.)
The appraised value of the boat is irrelevant. What matters is how much you paid for it and how much it was sold for.
(Just a comment: If you gave your boat to your ex-wife because the divorce settlement says you would, I wouldn't exactly call that voluntary. But as far as taxes are concerned, if it was part of the divorce settlement, it doesn't matter if it was voluntary or not.)
