Just thought I'd spread the word about how impressed I am with the Digital Yacht ANT200 AIS receiver (pictured below) that I recently bought through Malthouse Marine for a very reasonable sub £200 price
(you can pay me in beers Mart
I'd been toying with the idea of adding AIS to my plotter for a little while now, more just for interest than any real necessity, but after a recent trip in bad vis/fog I could see the advantage of knowing the name and MMSI of nearby large/commercial vessels to be able to call them on VHF if needed. There's a load of different AIS units on the market, but the ANT200 was small and simple to install with literally two wires to connect to the plotter and two to power. It draws 0.09 amps from my bench power supply.
Seeing as my boat is out of the water for winter I set it up on the window cill at home to see what I could pick up (2 miles from the coast). The unit is advertised as having a 10 mile radius for reception, which I'm pretty sure is accurate. Pics below show vessels in harbour some 3 miles away and the Condor Clipper en route to Portsmouth some 8 miles from me. There was hardly any setting up required on the Garmin, other than selecting 'high speed' nmea input and you then get prominent red triangles for every transmitting vessel in range. You can control which level of zoom these will show up on by tweaking the plotter settings and you can adjust the length of the speed/bearing indicator line to suit so you'd have an idea of how far it will travel in your chosen timescale. The only downside is that it is nmea 0183 rather than N2K, but I think most plotters still have 0183 inputs available.
All in all, a simple additional bit of safety equipment, especially if you can't justify going the whole hog and getting radar. It's clearly not the same as radar, but it's a step in the right direction.