As long as it isn't American-flagged, a boat can visit Cuba for years without being subject to importation duty. But a Tourist Card, the Cuban equivalent of a visa, is valid for only 30 days. It can be renewed once, a process that can take an hour or three days. After that, you have to leave.
When the Tourist Card expires, one option to reset the clock is to take a break from Cuba, whether a weekend buying spare parts in Cancun or an entire hurricane season in a cooler climate.
The catch is that someone has to pay a marina for the entire duration of the proposed absence. In advance. That might mean hundreds or thousands of CUC. (While Cubans might want to accept American-bank credit cards, the only place I have seen it work was Cayo Largo.) To leave without paying is to risk confiscation of the “abandoned” boat.
According to the Cienfuegos Guardafrontera, the boat isn’t supposed to be on the hook while you’re out of town, either. This is becoming problematic as charter vessels occupy more dock space there, leaving the marina with fewer than ten slips while dozens of boats anchor out.
The one loophole is a service known as Guarda y Cuidado. A captain can contract with the marina and a marinero, one of the highly-qualified Cubans who are allowed on foreign vessels. The marinero takes responsibility for the boat, its contents and any work being done. The marina gives the captain another kind of break — thirty percent off the dock bill — along with peace of mind.