I've been cruising the past couple of months from northern
sweden, through
denmark and now
germany relying 100% on the
Navionics app for my
iPhone 5c. It has worked flawlessly. GPS is spot on every
single time, even without signal.
Make sure you get the 3G version of iPad, otherwise you don't have the built in GPS chip.
You will see your position live on the map as you sail along. Boatspeed measurement is also accurate.
I downloaded the Navionics for my
iPhone as well as my iPad mini (no GPS). I use the mini for planning where to sail next (check out the harbours, plan
route etc.) - If you're signed in with the same Apple ID on both devices you don't need to
purchase the maps twice. Best €40 investment I have ever made.
I would never consider
buying a fixed GPS device (garmin/simrad etc..) for my
boat. The app just works too damn well along with iphone/ipad.
Of course make sure you get a waterproof+shockproof case if you want to check your
route while sailing along. I have a Lifeproof case for my
phone so I can check my position no matter the
weather.