Tons of people will let you charter thier boats for any length of time. Often times people get these boats with the intention of making up part of the cost by chartering htme out to people, cause they won't be using them all the time. If I were going to take a RTW trip I this would definitly be my preffered way of going. Assuming you are interested in boating under sail, this
site is a good resource. They focus on the boating scene in Northern California.