<Mike wrote: The range of AIS is not set in stone. 50 miles is a bit of a stretch under most conditions.> I understand all this, almost, as it's the same as a VHF radio. Offshore with the squelch almost wide open I've heard ships well over a hundred miles distant...never a thousand tho. I am curious about the range that folks are getting there AIS and with what type of installation. Seems that real world data is hard to come by when you push the manufacturers. This is why the question to Ice Dancer. I would like to have some reasonable basis to determine at what distance we should get a hit on a ship. The IMO seems to think 40 miles nominal, the USCG 30-50 miles or 30-40 miles or some other range depending on where you find it on the USCG or other government site. It looks like with a 23 db antenna at a base height of 15' or more is required to get this range if then. Perhaps the 80-100 ft height of the antenna farm of a big tanker! None of the manufacturers seem to think so if you read their info. "a 3db or 6 db" is generally the recommended antenna. I haven't seen any saying that to get the specified range you need a 9 db antenna at a height of so and so. As always YMMV, Cheers Dave & Nancy Swan Song Roughwater 58 Puerto La Cruz Venezuela