I use my iPad with a Dual (brand) WiFi GPS in the airplane. I carried paper charts for a long time. Now I pay $100 a year for all the charts instead of $100 every 56 or 28 days for a few charts.
The best thing is now my plane is geo-referenced on the actual chart (scanned) in by the company (wingX).
I don't know of there's a comparable app for boating, but there should be.