We use ICW around Hilton Head quite bit. For the part from Beaufort SC to Savannah, just follow the channel markers, all clearly marked. If you are outside and need to duck in near Hilton Head, I would use the Port Royal Sound at the north end of HHI, not Calibogue Sound at the sound end near Harbor Town. Port Royal is deeper and marked.
If you go south from Hilton Head on the ICW, the only area where you need to be extra careful is entering Fields Cut. If going south on the ICW, at the entrance of Fields Cut, you will pass G-47 on your port side, and G-48 on your starboard side. You will then see R48A that will appear to be about 50 feet from shore. You must then pass R48A ON YOUR STARBOARD SIDE going south. It looks out of place, it is not. See attached picture. My vessel's starboard side going north at Fields Cut is about 60-70 feet from shore. Look at all the water off the portsde of R48A - hopefully link works. https://connect.xfinity.com/appsuite/api/image/mail/picture?folder=default0%2FINBOX&id=323221&uid=IMG_4258.JPG&scaleType=contain&width=1024"]https://connect.xfinity.com/appsuite/api/image/mail/picture?folder=default0%2FINBOX&id=323221&uid=IMG_4258.JPG&scaleType=contain&width=1024