I've been using my old 3GS iPhone with navionics for navigation also my old Garmin gps map76 as a back up. I'm now considering a larger screen option because I now need glasses to view both...
I think that you should keep your gpsmap76 for rainy day use, and for dry conditions consider an iPad, though I'd also encourage you to consider other tablets (Win8, Android) unless you are 100% invested in iOS with your phone. Part of the benefit of using a tablet is the ease with which you can move route, track, and waypoint data between a computer at home (where I do the vast majority of my planning on the nice, big screen) and the tablet that you will use on the boat. IMO, iOS is too closed a system to move the data effectively. Win8 and Android offer you much easier options for sharing data via gpx files, for instance.
And daylight visibility is poor...
I agree that one needs to be careful to select a tablet that his strong backlighting and good gamut. But the brightest ones out there (iPad, Lenovo Miix2 8", Nexus 7) are equal to many turnkey chartplotters that I have seen. You can also purchase matte finish screen protectors, if reflections are a problem for you.
You should also install a 12v socket in your cockpit, so you can run the tablets at full brightness without losing battery life. I wired a 12v pigtail through my steering pedestal, back to my battery.
...the industry generally does a poor job supporting waypoint/route sync between different brands / applications.
I have had no problem transferring things between Android, Windows, and my Garmin handheld via gpx file format. I've also succeeded at transferring NMEA data via RS232, USB, Bluetooth, and WiFi.
Unfortunately, I have not been able to transfer any data in/out of my iPad. What I do in iPad, stays in iPad. Maybe other software would do better, but I moved on to more flexible options.
I am seeing fewer and fewer reasons to buy a chartplotter with every year that goes by...
I agree. Phones and tablets could make chartplotters obsolete just like they have done for dedicated car GPSs.
...AIS can be networked to a tablet with relatively inexpensive wifi multiplexer...
I would be interested in what mux you use. All of the ones that I have seen are pricey. I'd like to consider one if it's at the right price. Brookhouse's website has no price list, and my emailed request for quote has gone unanswered for over 6 weeks.
Up to now, I have avoided this issue by sending each instrument signal to my computer separately via multiple COM ports. USB/Serial converters are dirt cheap, so you can do a lot of them for very little money. Bluetooth/Serial converters (which I use) are a little more expensive.
These inexpensive options are vastly greater working with a Windows laptop, netbook, or tablet, because all the chartplotter software supports data inputs via emulated COM port. Most also support WiFi. iOS (iPad) severely restricts your options for this.
...The big advantages to a tablet are free or inexpensive chart updates, non-US chart add-ons are much cheaper, the screen size, and the multitude of other uses the device can have when not sailing. Also the price is a big advantage considering a chartplotter with a 10" screen costs as much as 3 or 4 4G enabled iPad airs...
SO TRUE. For US sailors, I also like the ability to use real NOAA charts, downloaded directly from NOAA's website, and updated for free as often as you want. This eliminates the delays and costs in updating proprietary chartplotters, and also the transcription errors when the chartplotter company copies over NOAA's information.
...I believe the only options for getting radar on a tablet are to either buy a wifi enabled chartplotter and link it to the tablet (which defeats the purpose) or to use a windows tablet running OpenCPN with a radar display plugin (which is not officially supported by the radar manufacturers)...
More and more I am hearing "that can only be done by using OpenCPN." That software just gets better and better, and has totally displaced Garmin HomePort and iPad Bluecharts for planning trips. And it's totally free! It is so nice to fire up OpenCPN on my big-screen home computer for planning, and transfer the routes to my tablet running OpenCPN in the cockpit. I also transfer them to the Garmin handheld, so I have the exact same routes on everything. And it's nice to know that my routes on the handheld were actually plotted using NOAA's charts - that eliminates most of the concerns that I have over Garmin's inaccuracies in their charts.
Ok so how do you get an ipad to recieve NMEA data from an autopilot or AIS and what's a wifi multiplexer?
Actually, you want to send data from the chartplotter to the autopilot, not from AP to tablet. The AP can use incoming route, location, and speed information to steer the boat.
The WiFi mux is about the only way to get the data into the iPad. For Windows or Android, you can get data in/out via Bluetooth. For Windows, you could do it by USB, as I described above (maybe Android too, not sure about driver support). The older NMEA 0183 standard is very easy to do on Windows, because it aligns very well with the old RS232 COM ports that Windows/DOC have supported for 30 years. Windows has adapted to USB and Bluetooth by emulating COM in the OS, which takes a lot of the headaches out of it.