Attempts, yes -- there was the 767 that was hijacked and ran out of fuel off East Africa. It attempted to ditch and sank

http://www.airsafe.com/journal/issue6.htm has a whole lot of information, including the fact that there were actually some survivors from this incident, and a couple of other ditchings.

[This message has been edited by marlborobell (edited Mar 04, 2004).]