radar schmadar
If the equipment is installed and functional, radar should be turned on whenever it can provide additional information to the watchkeeper which will enable her to keep a proper lookout. Unfortunately, most recreational boaters who have radar, do not have the experience or training to properly use it. It's a good policy to leave it on even in great daylight conditions to learn how to adjust and interpret the images. At the very least, read the manual carefully and understand the use of all the adjustments. Get as much experience as possible so that when you really need it in fog or at night, it can help you. Modern low end radars have a lot of the software which was originally developed for military units and can do amazing things, like track multiple targets, warn of impending collision, etc.... but adjustments are still critical. So practice, practice.