never give up, to succeed in any aspect of life , takes a lot of hard work, especially going self-employed. Decide what skills adn interests you have and write them down on a sheet of paper, then see if you can possibly make money out of any of them. Once you have decided on something then think of a business name and get cards printed as that always looks professional. Always try to be presentable as sadly folks do 'judge a book by its cover' if it is going to cost them money.
A very simple business i set up a few years ago was a gardening business, i only did basic gardening cuttin lawns ectera , keepin the gardesn tidy but it was a good way to earn money. Living on a boat should be no obstacle as long as you prepare yourself properly and irecon you will get more good advice on here. Good luck with your venture and remember 'nothign ventured, nothin gained'