You could just put the Navionics web map URL as a favorite in your phone. It's free but you need a cell signal to use it.
Start here:
https://webapp.navionics.com/?lang=e...y=cyeiGl%7CsrL
Or use
https://winnigas.com/gasmap and click the NauticalCharts button, but the Navionics link allows locations to be saved.