For serious sailors, this is a great app – Wärtsilä iSailor Review

I have 35 routes around Savannah, Georgia which I use on a motor boat at 25 knots. Easy to follow. I just completed a 900 nm passage from Tampa, FL to Savannah, offshore in the Gulf and Atlantic. All the planning and onboard navigation was done on an iPad with iSailor (with considerable prudent backup that was unneeded). This included three unanticipated ports of call which required rerouting while at sea. Excellent accuracy, even in tight quarters. (However, pay attention to expected GOS accuracy). The skipper said “the nav job was fantastic.” There is a reasonable learning curve to iSailor because this is a sophisticated, prosumer-level product. There are numerous app-purchase chart packs and instrumentation add-ones. If you just want to go around the lake, the app is overkill.
Review by short tack on Wärtsilä iSailor.