If you have a tablet (iPad or android) without GPS you can get an external GPS device and connect via bluetooth. I see the Bad Elf unit mentioned.

I use both Garmin and Navionics apps. Garmin base charts are better in some places and it has Active Captain integration. Navionics has Sonar charts. I use a RAM mount and a SUPCASE to mount at the helm. I have an external battery for passages. Works pretty well.

Cheers, RickG