flipflopper

Until I can relocate to Florida, I always try to do back to back cruises to save on airfare costs, but Covid may overly complicate my cruise calendar ☹️

I'd add this: I'll argue there's 99.9% chance that at start-up, to board, you'll require proof of vaccination or a negative COVID test possibly both. CLIA announced back last fall that all member lines had agreed on a requirement for COVID testing prior to boarding for both passengers and crew members. Several lines have announced all crew-members will be vaccinated. One line has announced all passengers and crew must be vaccinated. You may be able to use a post-sail RAPID Antigen test from your first cruise to board your 2nd cruise. But it gets complicated. See below.
It is less certain whether the requirement for testing will be a PCR test or a RAPID test or even required if proof of vaccination is required. I've read several articles on governments, mostly in Europe, struggling with how to implement "vaccine passports." One of the technical issues identified in the public domain, among many that Europeans working on this are dealing with is that new variants, capable of re-infecting vaccinated people, are out there. I want to emphasize that whether you can acquire a variant after vaccination AND transmit it is far from certain. There is anecdotal evidence that can happen but (1) such re-infections are rare and (2) symptoms have been mild and that implies low viral loads possibly not transmissible at all. Lots of truly unknowns here that we'll learn more about in the next 3 months.  
if it is required for boarding, there is plenty of uncertainty and an equal amount of confusion regarding terminology even among infectious disease experts. For example, what kind of test, how far in advance can you get it, will it be provided by the cruise lines in the terminal at check-in, will there be an added cost to you from your cruise line. Again, lots of unknowns that are being called "technical issues." Regarding terminology review this here - its from the CDC and IDSA (Fauci's home and in this case he's precise). These are US Government official terms but you may not find them being used routinely if you ask a clinic, for example, what should be a simple questions, "what kind of testing do you do. You may or may not get the answer you need.  https://www.idsociety.org/covid-19-real-time-learning-network/diagnostics/rapid-testing/  
Where are you sailing from? Port Everglades in Fort Lauderdale and Port of Miami have nearby, no appointment needed COVID testing clinics offering both kinds of RAPID COVID Tests. A Google search around the port you are leaving from will tell you what you need to know if you need to get a test on your own. The short of it from the link above is that there are both RAPID Antigen tests (results in 15-30 minutes) and RAPID Molecular tests that don't use the same Reverse Transcriptase Polymerase Chain Reaction (RT-PCR) process but have the same diagnostic reliability as a test done using the RT-PCR process have. It's the RT-PCR process that takes up to 72h for results. RAPID Molecular tests that ID the same COVID RNA that RT-PCR tests do with the same reliability produce results in around 30 minutes. They should both be acceptable, hihg reliability, diagnostic tests. Terminology caveats apply. I've seen these advertised. Compared to a RAPID Antigen test that costs $50-100 and Medicare covers them (as well as the RT-PCR tests), the RAPID Molecular tests cost upwards of $250. Medicare probably doesn't cover these. Commercial insurance might.   
Sorry for this long post but none of this is simple and it deserves thorough explanation so you've got some of the facts on the question you asked available to you. 

I just went back through a live blog from the Quantum sailing in Singapore in December. The writer was sailing a back to back and was required to have an onboard PCR Covid test on the last sailing day of the first cruise as well as a rapid test the day of debarking/embarking. That does give me some reassurance that I won’t have to find my own PCR test in port somewhere.

I just went back through a live blog from the Quantum sailing in Singapore in December. The writer was sailing a back to back and was required to have an onboard PCR Covid test on the last sailing day of the first cruise as well as a rapid test the day of debarking/embarking. That does give me some reassurance that I won’t have to find my own PCR test in port somewhere.

I just went back through a live blog from the Quantum sailing in Singapore in December. The writer was sailing a back to back and was required to have an onboard PCR Covid test on the last sailing day of the first cruise as well as a rapid test the day of debarking/embarking. That does give me some reassurance that I won’t have to find my own PCR test in port somewhere.