I had a marine aerial and like Tarbat, found that my Discone mounted outside on the chimney, at half the specialist aerial cost, is far better on AIS. I'm 12 miles inland, but can see to the 40 mile radius, i.e. 25 - 30 miles out to sea under flat conditions, and sometimes as far as Rotterdam under a lift! I don't use an aerial amplifier, that picks up every thermostatic blip and corrupts the data. I do use top quality coax though, UR67 when I bought a 100m. That has been superceeded with lighter, and no doubt a more user friendly replacement!