Sundrop is right. The shoals and sandbars move around too much to rely on any inexpensive GPS or even depth finder. You'll be on a sandbar before you even realize it. I have a 17' skiff and I had to walk mine off plenty of times before I learned where all the "danger areas" were. If you stay in the channels between the markers you'll be OK but around shackleford and the sound and harkers island and North River areas, your depth finder will go 18...15..12..10..2..1 in about 30 seconds.
Outside the marked channels you'll have to literally drive with your eyes constantly on the depth finder, especially in the sand dollar island area and horse island and shackleford area until you learn where the sandbars and shoals are *supposed to be* even though they shift around. If possible I like to schedule my boating trips on the low tide so I know I got water coming in if I soft ground.
And if you like to anchor close to the beach and swim, mind the currents thru the area. At Shackleford and sand dollar Island you'll want to beach on the downward-current side of the sandbar. I learned very quickly that the tides move in or out with a lot of force and beaching on the up-current side of the island or sandbar will push you up on the beach and ground you. I got stuck like that one time and the harder me and my dad tried to push it back into the water, the more the currents and wake from passing boas beat us back onto the sandbar. My skiff was light enough we were just able to lift it up and "get some water under it" and get it back off. If I hadn't noticed it and cauht it before it got closer we would been screwed.
I saw a guy last year with what was probably a 22 foot boat and he had beached on the up-current side with his family to swim and play on the sandbar and the currents thru the sound had pretty much pushed him up onto the sandbar and he was literally on dry ground. He was trying to push it off himself and I stopped to help him but I knew we had zero chance of pushing it back into the water. Felt bad for the guy and he didn't have seatow or boatus so the pirates probably raped him for the ungrounding.