If you want to donate just to be generous to a worthy organization, that's great and there are many reputable charities that would be happy to take your donation.
If you want to donate because you're having a hard time selling and you're hoping to make out good financially, you won't. Most charities auction off their donations and what they get (usually well below market value) is all you can deduct from taxes. Let's say your boat has a market value of $5000. When all is said and done, the charity will probably be lucky to get $3000 at auction, which means you can only take a $3000 tax deduction. If you are fortunate to be in a high income tax bracket, you will only see about $1000 in tax savings.
So bottom line, financially, you are better off having a fire sale on your boat and getting rid of it before you incur any more expenses.