I have used both the iPad and an Android based Nexus 7 for navigation. I use Navimatics for the iPad and MxMariner (loosely affiliated with OpenCpn) for the Nexus 7. OpenCapn is not available for the iPad or the Androids.
Both are basic, simple navigators without all of the bells and whistles of OpenCpn
or the heavier duty commercial
programs. But they both work fine. I never use routes and on full featured chartplotters rarely use single
waypoints. Both are available on these products but I can't tell you how they work.
But I just point the course arrow where I want to go, or alternatively find the necessary bearing to get where I want to go and adjust the boat's actual COG to match.
I can't recall
how the iPad does charts
, maybe it downloads them as you go because the iPad with built in GPS is also the one with 3G so internet
connectivity is (almost) always there.
MxMariner on the Nexux 7, having only wifi
connectivity, allows you to download one or more NOAA chart regions so that the cartography is always available. It takes a fair amount of memory, about 300 mb per region, so you may want to buy the higher memory Nexus 7 if you want to use it up and down the east coast
I like them both, they work well and both are great backups for installed chartplotters or stand alone navigators for casual use.