A -GPS is Assisted GPS, it means the GPS receiver uses something else to help with the fix. It may be WiFi dat or cell phone provider data that would narrow the fix and speed up an accurate GPS fix. Lots of people here use tablets for navigation. For me, I use a mixture of paper charts & electronic. I have an android tablet and have loaded the free NOAA application and all charts from the gulf of mexico. The built in GPS of the tablet would be better if the application was a little more user friendly to plot a course on. I have a Garmin chartplotter that is super simple and the primary navigational tool I use. The paper charts consist of a mix of recent and older charts plus cruising guides.
There may be some complicated methods to interface a wireless tablet to ship's instruments, but a simple fish finder will be much easier on the pocketbook. You can't use a tablet to replace the VHF, but you may be able to interface a wired connection and deliver NMEA data to your VHF for DSC, but again, more trouble/money, and no doubt less reliable. If that's your intention, just get a relatively cheap handheld GPS and use that. The single best thing you can do for VHF performance is to put the antenna as high as possible. A typical VHf transceiver with antenna at the masthead will perform well.
I like not depending so much on a single device to do everything because when it fails, everything is failed. That's why I keep a tablet, chartplotter, two handheld GPS's. 3 VHF radios, cellphones, paper charts, cruising guides, compass & a sextant that I forgot how to use.
I rarely venture beyond sight of land and could generally get where I need to go without any of the above. I used to do it without as much on my H23.5, but I wasn't worried about running aground.
