Read Webb Chiles's recent articles, as he is based out of Opua, NZ. He has done five circumnavigations, including an aborted one that was about 11/12's complete in two open 18' Drascombe Luggers. He did this in two boats cause the first one was confiscated by the Egyptian government, and he was sent the second one so he could continue.
A lot of this depends on the boat... a better boat will take care of its crew... a bad boat will get its crew killed. A lot of this depends on your skills. There have been many who have thought of doing something like this but didn't do the proper preparation and failed miserably. Ken Barnes, David Vann, Heather O'Neill, and Ronnie Simpson come to mind.
Ken had a fairly decent boat, but IMHO wasn't prepared, and the boat wasn't prepped properly. In his one knockdown, the batteries (4Ds IIRC) went bouncing around the cabin and smashed out hatches and such... IMHO, the boat was too big for him.
David Vann, who thought of Barnes as a role model, was an idiot that didn't have a clue about how to design a proper trimaran and his faulty design started to break up in 2' seas with 15 knots of wind or so....
Heather had a great boat—one of the last Flickas built—but she didn't prepare herself or shake the boat down properly and aborted her voyage basically one day after leaving. She managed to get herself locked out of the cabin in heavy weather and had to hack a hole in the boat to get back in IIRC. She failed her boat, not the other way around.
Ronnie Simpson was more concerned about his media capabilities and timed his departure, not to a weather window, but to make the evening newscast. He bought a fair bit of HD video gear to document his voyage, but couldn't be bothered to get a 40-something year old boat surveyed or inspected....
Donna Lange, on the other hand, was a sailing novice in her early 50s when she bought her Southern Cross 28 IIRC. She gradually worked her way up from daysailing to a full-blown circumnavigation. She was one of the boats that responded to Ken Barnes and went through much the same weather systems as he did, in a much smaller boat, yet had no issues... because both she and her boat were prepared properly.