I see a lot of 'tech' ideas to get around. If you want to be fuel efficient as the topic suggests, there is really only one answer. Today's sailboats can get you around in any direction at adequate speeds. Some of these suggestions assume oil will be plentiful and available; and I suppose reliable. A 55 foot mono hull sailboat can get from Newfoundland to Ireland in 8 days. A good catamaran can do it in less. Most decent designs can do 200-240 miles per day. How fast do you want to go? The fastest cats can do better than 60 mph. Somewhere in between should be fast enough.
I building a 49 foot catamaran houseboat to live on (I also think housing in a sea-stead should be mainly your own boats, too---so you don't have to be a millionaire to live there---rents pay for the fixed platforms where manufacturing, business, retail, and farming is done) that I expect 180 mile days using fiberglass (for UV resistance) junk-rig sails. Mostly plywood, and covered with a thin (12 oz) layer of fiberglass, and for less than $75,000. Lots of redundancy if everyone has their own boat. Put together, they could even pull the fixed platforms back to 'station' if it got loose.
Maybe I'm old fashioned, but high tech assumes a lot of things stay just the way they are now---and I don't think that will be the case.