Open cpn can also be put on andriod smart phone or tab with gps (note GPS on a samart phone/tab is not the same as network location... check in the location settings of the unit, dont take the word of a 'trained' sales person.)
Opencp maps are the NZ linz maps converted, the download is now a few yrs out of date.
There is another maxsea (?? think was called) been a few yrs since looked at that but very similar to opencpn.. again very basic LINZ maps converted.
yeah, I know about the webapp
cant do it for offline planning, which is what I want to do when away from coverage
If coverage or not, doesnt matter the navionics web app doesnt do the routes and tracks like the smart phone/ tab does.. its only about $20/ annum and $10 there after..
And doesnt require any coverage coverage .. other than gps to work...
It is like google maps, you can select and pre download huge areas for off line..
again it is location by gps, NOT the coverage by cell phone tower/ wireless to locate.. if the tab doesn't have gps, navionics usually tells you it is not compatible with the unit if you go to load it.
Navionics on a tab/ phone @$20/$10 is fare more uptodate, detailed cheaper than buying installing a laptop gps and out of date max sea/ opencpn maps.
I have run all of these, and a couple others on windows computers / android smart phones and still occasionally go back and check them out for significant changes every now and then over the last 7 or 8 yrs..
Basically I started with the same, and a couple more questions you originally asked.
Edit: opencpn has a habit of getting stuck and/or dropping the zoomed in Linz map sheets.. only way to fix is the reload the maps... and thats a pain if 1/2 way thru a project..