1. Radar/Chart Plotter Overlay
Most GPS/chart plotters with radar have the ability to superimpose their radar picture right on top of the navigation chart. This gives you a living real-time picture of nearby boating traffic and other objects that appear around you. All you need to do is connect an electronic compass or heading sensor with a suitable output rate (from $600) to a plotter. In fact, in most cases the compass signal from the autopilot will do the job just fine without additional cost.