Even as a European from the EU and from the Schengen countries, you will still need a visa in order to visit certain countries. Unfortunately, the USA is one country where everyone entering via boat still needs one, the normal "Visa Waiver Program" does not apply.
There is a website called
Noonsite which lists the requirements for most countries in the world and is a very useful resources and kept reasonably up-to-date by receving appropriate information from cruisers.
Almost every country has its own forms to fill out, often with several copies. As mentioned above, one flies the yellow "Q" flag upon entry and only replaces it when all formalities have been completed. It is funny to see huge freighters and other behemoths flying a tiny little yellow flag, but even they need to adhere to the same regulations. Usually the steps to clearing in involve immigration (who check the people), customs (who check goods), those who check the paperwork (to make sure the boat paper match and the clearance out of the last port is correct and timely). If you are lucky, these functions are all done by the same person and/or in the same office. As often as not, one needs to travel all over the port to different offices in order to complete the checkin process. And then, upon leaving the country, you need to do the rounds again in order to properly check out and be able to present those papers to the next country upon arrival.
I've cleared into countries in 10 minutes (USA,St. Barths) and others have taken hours (Nevis - but mainly because I had a broken toe and couldn't walk the 2 kilometers between offices very quickly).