With the Navionics iPad app with added maps you are buying a one-year license with continuous updates during that time. You do need to kick the update off by going into the map menu and choosing "Update All". I have three maps - UK, Europe and US/Carib - I usually have about 100mb of updates per week that get downloaded.

The base Navionics maps are not changing. The user supplied Sonar Charts and user updates are what are changing. You need to decide for yourself how much you trust those.

For the BVI, I have seen new wrecks and buoys pop up within a day (Dawg Rock Buoy and the wreck last year off the Anegada Channel.

I certainly am not going to use the Sonar Charts as gospel, but they do give some interesting additional information to use for your pilotage.

p.s. need to fix that ticker at the bottom of the page - we are wheels up tomorrow!