Good question
@rgranger.
Radar is a wonderful feature to improve your sensory awareness in vision limited environments like fog. Various things seem to appear out of the gloom and not all of them appear on radar.
May 4th 2017 this stealth boat showed up 75 yards from my starboard mid ships, doing 30 plus, out of the fog. Did not show on radar (basic analog, no dopler). Was not on the AIS.
That is my buddy
@LeslieTroyer with his Catalina 36 in the back ground. Thank God he was there.
Nothing will stop the fool not adhering to the Coast Guard ColRegs of slow speed, lights and a horn or bell when moving in limited visibiltiy. I was just lucky not to die and my boat only sustained minimal damage. Note the light on the fishing boats starboard bow. Yes it is missing. Ripped off as it struck my stern pulpit.
Sailing in fog is work. Your mention of the channel markers suprising you. I'd encourage you to not venture close to channel markers while in the fog. They are magnets for other boats with autopilots. They follow the channel markers as if they were white lines on a highway. Better to chart your course to give them some space so you are not on their line.
Radar is great to identify land masses (when tracking on a chart) and the bigger boats. It is the fleas that can bite you.