I do a lot of hillwalking and use Viewranger for plotting and tracking progress, which got me thinking on what's available whilst out on the boat.
I found Navionics....it seems good.
Plenty of info and live data, I'm guessing the live data will require an adequate signal though.
You get a free trial for 2 weeks so why not give it a bash. Probably an overkill for plodding about the coast but you can never have enough info!!