sometimes to track hazardous traffic at night or in fog, sometimes to track another boat I am "racing" (because it will tell you your speed difference). Mine is a Raymarine 2KW dome from 2007. You need a fast heading rate sensor (usually the autopilot). It works better on a big target that appears on every scan, and also better when your heading isn't varying a lot. That means it does' work very well (for me anyway) in a big seaway and weather: return is not as reliable, high yaw rates make it hard for the Marpa to track the azimuth. AIS works a LOT better, for boats that have AIS.

I am about to ebay the 2KW dome and install a 4KW HD dome in its place, that might make it work better?