It's not going to be easy I know, and I give you the advice very matter of factly, and sometimes relationships are not very matter of fact, but far more emotional. If you really care about someone, it becomes difficult to confront them, for fear of losing them, but you have raised children, and unfortunately there are times when you will have to approach your relationship in the same way. If you don't open a dialog with him and get all of this stuff on the table, then you will start to resent him, and he will probably be doing the same thing next year. Can you imagine? Being in this exact same position a year from now? Because he is basically ignoring it, that tells me that unless something happens to put him on a different path, he will continue to ignore it.
As for the boat...I'm not sure to be honest. My thoughts are basic math.....sell the boat for what he owes, plus the storage fees, and that's it. Maybe that's wishful thinking....since the economy is so bad, and I don't know if the boat is worth what he owes.
The second choice would be to get caught up on the storage fee, so that he could sell it. If he sold it for 15k, then he would owe the additional 3k, but that beats having to pay the whole amount.
The third choice would be to sell it for less than the 18k and have the buyer pay the storage fees and deduct the storage fee from their payment. Again, he loses money, but not 18k.
I would pay that storage fee as soon as possible, especially with them adding late fees, or eventually they are going to wind up owning the boat, and he's going to have to pay over 20k between the boat and the fees.
Widen your selling options, put an ad in the paper, put an ad on craigslist.com, put a listing on ebay if you have to (through and auction house might be best, XXXXX XXXXX sure it goes thru ok).
Let me know your thoughts about this. (I'm not worried about you paying, you've always accepted in the past :)