His question has stuck with me though, and given our pattern over the past few years I would say if I HAD to make a choice, I would likely pick an AIS receiver.
We have used Radar a LOT, but that was mostly back when we traveled at night when we were on the Columbia River. It was a great complement to the chart plotter - being able to look at shorelines. And it also allowed us to keep track of tugs and their pushes, as many of them would 'Turn off that darn AIS' once they crossed under the I-5 bridge. (Was told by one captain that AIS was not required above the bridge...)
To be honest, it is mostly the Ferries we look out for, as they are FAST. And even when they are not moving we can pull up the detailed screen for them and see when their SOG moves away from 0 - then we KNOW they are getting underway.
And the times in the Fog we have used the Radar we have noticed:
- We already knew where the Big Boats were via the AIS
- We knew where the shoreline was via the Chart plotter
- It was all but useless for small -fast- boats.
Yes, we use AIS a lot. And with a low cost ($200) receiver that integrates into our existing PC based chart plotter - if I was forced to make a decision I would likely pick AIS over Radar.
But even with our experience of Radar in the Fog, given that a quick check on Ebay shows a couple of 1731 units with bids under $300, I still stand by my original Both comment. If nothing else, it is a great backup to the AIS / Chart Plotter for land and big ships!