Stay out of the entire charity drive and contribute nothing. Let the charity auction committee make all the promises. When the original sailing agreement isn't held up by the committee (probably because they forgot to schedule anyone and lied about it) you find who won and give them all a call to join you as you are a nice guy. You haven't made any promises to any institution or committee so you should be safe with just friends aboard.

Damn, I wouldn't do it. It's just too easy to get into trouble.

But, we did support a local charity funded organization (The Ocean Institute) by just purchasing something at auction. It's easier that way and we have something special (to us old surfers in Southern California) for a couple of years before we put it up for auction again.