Quite often we are asked if our Wi-Fi Gateway is compatible with the Navionics Marine app. The short answer is no, because of restrictions to the app imposed by Navionics.
Navionics makes most of its money through its chart cartridges, and needs to keep its dealer network happy, who make good money on chart cartridge sales but obviously nothing from users of the Navionics app. But Navionics needed a way to show their user generated content, and producing an app is the obvious route to do this. But they realised that many users would just use the app on a tablet if they could, instead of a much more expensive chart plotter. So, to prevent this, they have intentionally hobbled the app so it can only get position data from a built in GPS, which effectively restricts its use to phones as few tablets have a GPS in them. Also, the app won't link to an AIS or to any other source of additional data.
Of course there are other alternative navigation apps. If you like Navionics charts, then I suggest you look at iNavX (now available for Android as well as iPhones and iPads) - it also supports other chart formats. For Android users, OpenCPN is also worth looking at; it doesn't support Navionics charts but does support a number of others.