That being said everything on this boat so far has been in the budget category. Cutting edge boat tops leaning post, 4" garmin sounder, Bimini instead of T-top,etc.
I bought a 8" Pantech Element tablet for 89.99 shipped. It has internal GPS,Wifi,HD video, and 4g sim card capable on AT&T.Search ebay for either a refurbished unit or used. This is an older tablet but has a dual core processor and is reasonably snappy for this application.
I have an ipad but I don't want it on the boat. For the price of a lifeproof case I bought this tablet.
I bought the software on sale for 19.99 a long time ago but think its 34.99 currently. It allows you to download any maps nationwide and gives great detail. You download the maps at home and they stay on the unit itself.. no data needed.
Ok back to the Pantech. It is rated for submersion for 30minutes @ 3.3ft. The catch is the ports for the unit must be closed to achive this. after a few outings with the unit on 24/7 I wanted the unit to be able to charge and stay water resistant. It has great battery life but I'd say limited to about 5-6 hours with the screen constantly on.
I removed the port cover on the USB side of things and used Plastidip to secure a USB cord semi-permanently(can be removed easily). This allows the unit to be waterproof and be charged. I also bought a mount from amazon for like $10 shipped. Its the suction cup style which I hate so I just screwed it to the dash. I also added velcro to the back of the Pantech and the mount. If you do this don't use the 3" industrial velcro if you want to be able to remove it easily. You could also just velcro it to the dash directly. Mine isn't the correct angle so I didn't.
Another bonus would be that the element records 720p HD video and pictures. The video is HD but marginal at best but the pictures turn out okay.
The cons are
Hard to see with polarized glasses
When wet the screen goes nuts... this can be a problem when you have wet hands.

Modification to USB port with plastidip

Soaking in the tub


Sample Video from the Pantech
http://vid181.photobucket.com/albums/x1 ... -03-29.mp4