Test Quest: http://zctut.com/raft.qst
(BTW, don't take the raft unless you're using 1137 or greater, you'll get stuck)
Basically, it seems that Link is capable of walking a full tile away from the shore before drowning. This is regardless of Z3 movement or where he walks from, or in what direction.
If you walk halfway out (that is, so you've just got your feet wet), and turn to the side, you'll drown. Same if you walk all the way out (1+ tiles out).
EDIT: Arrgh!!! I hate it when I post stuff in the wrong place. 😞(( I thought there was an option to delete a post...