Re: I love stuff like this..
"Engineers are confidently predicting that a wind powered vessel 'could sail indefinitely, at 2-3 knots average, depending on weather conditions".
Last time I remember the "pinnacle of wind" - the steel hull, steel mast windjammers from the end of the 19th century outsailed with ease german cruisers at the start of WW1. Germans could not catch up even with the sorry hulk which was Cutty Sark by that time (it had a mast missing and had 1/4 of the crew it needed).
The speed of these 4-5 mast monsters was ~ 15 knots. That is in fact on par with most cargo fleet till this day (only ferries and some container ships sail faster and only on short haul). It was not speed or carrying capacity that terminated the windjammer fleet - it was a combination of the canals (Panama and Suez) and manpower costs.
The saddest part about attempts to reintroduce windpower in ships is that none of it gets even close to where we were 120 years ago. Parachute sails/kites my a**e. A proper "salty dog" rig of the kind which took the route around cape Horn to California or Cape Good Hope to Australia in the 1890-es can run circles around it any day.
The only reason for wind to be slower in the end-to-end play is that it requires different routes. You usually cannot sail straight from A-Z. That is why the canals decimated it in the first place. From that perspective, considering where the Suez/Middle East situation is going lately we will be considering wind again very soon (same as we did during the previous Suez problems).