When we took the ferry to Uruguay from BA three years ago we got an exit stamp from Argentina then an entry stamp from Uruguay, right at the ferry terminal. It's when Argentine Immigrations about had a fit...I paid my $140 fee, got that stamped, and then got my baggage and cleared Customs. There was no actual entry stamp into Argentina!
Two years ago we took a cruise from Cartegena to Aruba, LaGuira Venezuela, Curaçao, Panama City Panama, and returned to Cartegena all in 8 days. As I understood it any and all fees WRT entering one of those ports were included in the cost of the cruise. Generally for cruise ships the visa requirement is either waived or stamped in your passport...