hello @Kingdw , 1 word - GAIA GPS APP FOR IPHONE, ok that's 5 words, but I just checked and they have USACE river charts, and NOAA charts, as a map download.  As well as all the functions of a GPS unit.

The big plus is, you're looking at your phone screen, which has much more visibility than most GPS unit windows, and you don't have to have another device to carry, charge up, etc.

good luck