Having c-in and out in 14 countries recently from Greece
+ almost all Caribbeans countries, all I can say that every country has different rules and even every port officers in the same country may have different approach to every case.. In Italy
in theory you need to visit a number of offices. Not the case at all, if you go to any marina you give an ID, insurance
and the boat papers. Noone has ever checked my passport or visa. (I need a visa for any Schengen country) They take a photocopy and giving you back. That's it..
The smaller and less developed the country the more buraucrotic they become. In Jolly harbour Antigua
two boats have had serious problems (5.000 ECD fine if I recall
correctly) as the wifes touched the land (to the bathroom in the same jetty of the custom office) before the husband hit the custom..
However many of these islands do not have a cost guard or whatsover to check it out. So if you anchor
in one of these places and hit the ground for drink or dinner , most likely you get away with it. The trouble is if you are involved in any trouble or get caught in some way you are deep S..T.
with few exceptions (Portugal, certain part of Greece) you can easily go on shore until business day if you arrive on weekends or after working hours.
Well for the US, don't even think of it