****It depends on how often you seek out the customs people to present them. They don’t “ask,” they don’t know you are within a thousand miles until you walk up to some office in a city and tell them.****
That might change if the SHTF, but I don’t believe the governments of the world are going to be expending many resources scouring the ocean for strays. Getting to know where to get supplies with minimal contact from other people sounds easy enough with some experience.
Borders are funny. 99% of people associate international travel with TSA lines, passports, shots, visas, customs officials etc, all done in an airport or possibly a cruise-line terminal. But in any case, in a big hall surrounded by armed cops etc.
That is NOT what crossing a border is like from the sea. It’s virtually on “the honor system.” There are no foreign “coast guard cutters” guarding the coasts. You just sail in anywhere and drop anchor in any port, that is physically what can be done. They only know you have arrived in their country when you seek out their customs office to “report in.” They don’t find you, you have to find them! Otherwise, nobody knows. Naturally, you would be breaking the law if you failed to “report in.” But hey, that hasn’t stopped 20 million illegals from coming to America and living openly but illegally.