I also had heard the ropes connection. This is supported by Dave Wilton. See http://www.wordorigins.org/wordort.htm#Three Sheets to the. The notion is not one of clear sailing as suggest by inselpeter's "going full speed ahead." but rather lack of control. This is expanded upon by the Word Detective here http://www.word-detective.com/back-p.html#sheets wherein he contends there was a full up hierarchy of lack of control culminating in "four sheets to the wind" specifying unconsciousness.