Is it possible to split the quarantine period? Specifically, start in a certified villa on Day 0, check out the morning of Day 4 and get the Day 4 test on the way to the boat, then sail to an approved anchorage while waiting for the results on Day 5. Thanks for your input

No you would be required to go to the boat on day 5 once you have been cleared , as the driver picks you up on day 4 for your test and takes you back to the same location and you are not free to move till you get cleared, sorry.

Still, for a two-week vacation, it might work - 7 days on land and 7 on the boat. cheers

We considered doing Day 0 to Day 5 in a villa before going to the boat, primarily because a few people may have to work and the wifi in the villas would be better that in the quarantine anchorages. We've scrapped that plan now and will be on the boat for the duration.

Does anyone have any suggestions on wi-fi in the quarantine anchorages? Do you know how you would get your Day 1 and Day 5 notifications if you don't have cell phone coverage and the wifi doesn't work?

There are now multiple ways to get Internet in the BVI. You should not have any real issues. Get a international plan for one or two of your cellphones. They can be set up as hotspots. The boat will likely also have onboard WiFi. Between the two you should not have issues. If you do get in a dead spot moving the boat a short distance should fix it.
G