Been using AIS on my yacht for Three years - its a $200 receiver that hooks to my VHF antenna via a splitter and runs a 38400 baud RS232 output to my chart plotting computer.
AIS targets are overlaid on my charts and the time and distance of closest approach is computed in real time. Anything that looks like its closest approach is within my preset range ring appears in red.
Only issues - updates are every Two minutes. Vessels under 500 tons are not required to carry AIS class A tranceivers. At least half the merchant ship fleet don't give a f*** about anything smaller than they are, they work on the "big ocean" theory, set the autopilot and go to sleep.