Question: I recently bought a small sailboat that has no GPS. My close vision is no longer the best. Could you offer advice about what GPS would be best? I would need a large screen, pedestal mount, no need to connect to boat power, and SIMPLE TO OPERATE! As an alternative to dedicated marine GPS, what do you think of using a tablet with APP for marine charts and GPS?
Answer: For a GPS display unit, you have many choices - but there are limitations in what you describe. For example, almost all large-screen models do require more power and therefore need a connection to a 12v boat battery. These get more expensive the bigger they get. You can get smaller, portable units that run off batteries, but these usually have smaller screens. I've used small screens for many years and have no problems with them myself, since you can always zoom in for a larger picture of the chart where you are - but you need to judge this for yourself if you have near vision concerns. I recommend visiting a big marine store and looking at the different models to see how big a screen you actually need. The bigger, the more power needed, the more expensive... But even the smaller portable ones have mounts you can install on your pedestal.
There are many good charting apps that run on smart phones and tablets. And Android tablets with a 7-inch screen are affordable, but make sure the unit has built-in GPS (you can run off a separate Bluetooth GPS receiver, but that gets more complicated). Here's an article comparing 5 different Android navigation apps.
I have used two of these apps myself. The downside to using apps on a tablet is that most tablets are not waterproof (so you need a sometimes clumsy case for boat use) and they can be more difficult to mount at the helm. Their battery life is much shorter than portable GPS units - but you don't have to hardwire them into the boat's 12v system. And of course you have to have a smartphone or tablet with a good GPS receiver (some don't work as well as marine GPS units). These units can be quite good for limited use when most of your navigation is by paper chart, but I'd hate to depend on one for primary navigation.
Finally, you asked about simple-to-operate GPS units. Unfortunately, almost all have become very complex as they add more and more features every year. I would advise not making this your primary reason for choosing any model. Instead, get one that meets your size, power, and mounting needs (and that includes charts for your area), and then have someone teach you the very basic uses, such as how to see your boat on the chart. There may be dozens of functions that you'll never need to use - so just ignore them, and learn the one or two things you do want to use. You'll find those easy to use after just a little practice.