You will need a U.S. Visa to enter the USA via sailboat, ESTA is not sufficient. The best method is to apply for the visa while you are still in the U.K., the process can take a couple of weeks and will not only cost a pretty penny but you will also have to travel to a U.S. consulate for the personal interview. They are concerned with people entering the USA and then remaining, so the main thrust of the questions is having you show that you have "ties" to your residence, and they can ask for things such as rental or homeowners papers or employment
contracts or similar items if they think that there might be a chance of overstaying. The visa, once you get it, is valid for 10 years (it might be 15 years, I can't recall
and my passport is on the boat) and remains valid even if the passport it is in expires.
Here's a good link to information: http://yachtmaster.com/crew/visas