You can use Navionics Boating USA $10 for your phone or $49 for a tablet. Gives you everything a CP does plus MUCH more. Not weatherproof or sunlight readable but there are many workarounds for that. Get a long USB charge cable and a weather resistant case (or food storage bag) and you're golden.
The newest updates make it super powerful with auto-routing, wind/weather, on chart real time tides/currents, even the displayed depths change in real-time based on present tide level. Plus your charts can be auto-updated anytime you have wifi.
If I had to choose between this and my CP I'd choose the CP only because of the integration with my radar and AIS, but for navigation this beats any CP hands-down.