Those that use the Navionics iPad app... Wondered how often the maps (BVI region, specifically) have typically been revised in recent years. It may well be on as 'as needed' schedule, but thought you long-time users may have developed a feel for whether it's typically been annually, monthly, etc. I wanted to get it for an upcoming trip but wanted to wait until I'm fairly sure the rev I buy will still be the latest when we leave the dock - rather not buy maps twice. Thanks in advance!