I have a Samsung Galaxy Tab 2 10.1 running Navionics and it is incredible to use.
100km offshore and it works superbly.
The only issue is I am having trouble finding a waterproof case for it.
There seems to be some good ones around for the Apple gear but not for Android units.Most that are available are mostly splash proof.
I use the Railblaza tablet mount with a starport base and so far it has been really good offshore in some horrible conditions.