I use both a Raymarine 7212 chartplotter at the helm, which interfaces/displays and overlays everything on the boat except the engine - wind, depth and speed transducers, compass, GPS, radar, AIS, satellite weather - and provides useful real-time information I find difficult to get from my iPad. It is my primary navigation instrument, and I update the chip every two years.
I also supplement that with my iPad, which I can carry anywhere on the boat, do planning ahead of time from anywhere, and which ties into a Yacht Devices NMEA 2000 wi-fi gateway which allows it to pull information off of the boat such as AIS. It really doesn't seem to pull the other data off the system reliably such as wind and depth. It will NOT pull the radar or satellite weather, and only AIS gets reliably overlaid on my iPad charting software. I use a couple of the common apps - Aquamaps, and Navionics mostly. The iPad has a GPS chip in it.
I find they both have their uses, but my view is they're complementary:
- The chartplotter allows me to selectively overlay things to get a real-time picture of multiple streams of information (e.g. chart and radar at night so I can be sure I'm not following a chartplotter onto land; AIS and radar so I can see the boats WITHOUT AIS as well as those with it). Its charts are out of date the day you buy the new chip.
- The iPad is so much more portable and intuitive I find I use it for a lot of things don't want to be at the helm for, or fiddle with nested menus. The charts are updated constantly - some are crowd sourced, depending on the application. But it does need to be recharged, and its not screwed down on the boat, so Murphy sometimes rules.
Last data point: I crew on a boat for a friend who owns a Hinckley 42 Sou'West. He's sailed it across the Atlantic, and on all the Bermuda races for many years. I've sailed on it up the East Coast offshore into Maine and up to Nova Scotia, and back from Bermuda three times. The owner is absolutely meticulous about his boat, and racing. He has a dedicated PC below with chartplotting software that he uses to plan and track each trip. But he uses an iPad in the cockpit - no chartplotter. We found it especially useful when navigating at night when trying to find the next lit buoy because we could sit forward with the autopilot control (wired) and steer from on top or just under the dodger while having the best view over the bow of the boat.
Anyway, see what works for you.