We have not done the Culebra trip since COVID began. There are some resources at
https://www.discoverpuertorico.com/info/travel-guidelines and
https://www.travelsafe.pr.gov/. These protocols state that you can enter PR without testing if you are vaccinated. However, their travel declarations are quite limited and do not accommodate the cruiser.
Returning to the USVIs, you still either need a recent COVID test. If you were vaccinated in the USVI and have proof of vaccination then you do not need the COVID test. Why? the USVI is seeing a high rate of fraudulent vaccination credentials and test results from outside the territory. Governor Bryan has stated that the USVI will accept vaccination records from outside the territory once the CDC issues secure vaccination credentials.
Cheers, RickG