A lot of people think they're checking out when the decide to set sail. You'll find it's not so--the requirements of traveling country-to-country mean the cruising boat will be dealing with not just one country's bureaucracy, but that of many countries. Money is something needed to clear in and out of country and you will need to carry your own weight in terms of having money for your own clearance as well as sharing in the costs of food aboard ship. Rarely will it be a barter-ride for crew unless that crew is unusually skilled (read "sailor") and bringing a lot to the ship besides a friendly attitude.
For the best results, suggest you learn how to sail locally (volunteer to crew for some of the racing boats at the local yacht club for example or take some lessons --you may have to pay for the lessons with real money though
) and then you'll have some skills that a cruising boat might be interested in having you aboard for. Those local sailors will know people traveling and they can hook you up with a reference as well.
Further, if you make some friendships with those racing skippers, you might find yourself invited on a few little overnight or fortnight trips. On those trips, you might learn if you get seasick or have other problems that will make your dream of hitchhiking the oceans less of a good idea.
Remember when you're out there trying to get sailing experience (local at the clubs at first or with a cruising boat) the whole conversation is about what you can offer to the team or boat--not about what you want to get from it.
So think long and hard about what you can really offer and what would be valuable to the skipper. You need to become a desirable hand to have aboard any boat. If you have no idea of what those things are--think about cooking skills, mechanical fix-it skills, athletic ability (going up the mast, even if someone is winching you up in a harness is not easy), strength, good health, ability to get along with ANY other crew members, ability to take orders and do what the skipper tells you to (the boat is not a democracy), a personal nature that is clean, neat, organized but yet doesn't care if the other crew members are slovenly or less than ideal. Ability to stand watch, ability to navigate (another thing you can learn with a class before you set out so you'll have skills to offer).
If you don't have a big ego, are particular enough to learn new skills and do things properly but yet have the laid back nature needed to not let oddities of other personalities get under your skin, you'll have a great time crewing.