I remember having the same problem 2 or 3 years ago -- sailing on SMP for more than a minute or two makes you more and more out of sync with the server, so you're prone to "crash" on beaches or squids that you thought were 20 blocks away, because the server thinks you're somewhere else. Super annoying to constantly break your boat with no warning, or to have to log out and back in every 5 minutes just to know where you actually are. /rant