As long as you are out of the direct beam of the scanner (so its above your head) i think you are ok with it on, the beam is very narrow obviously, as it is ommited from the rotating scanner, but at its highest strength. The stupid thing is, most of the radar arches on flybridge powerboats are designed so that when a radar is mounted, they line up directly with your head! People I know with them will not run with them powered up and guests on the flybridge for fear of frying them!!
If you go into most marinas and especially locks such as port solent on the south coast they all have signs requesting that your radar is turned off whilst there. I guess if you are exposed all day to the level of radiation that is emitted by radar then it probably would start to take effect. (not good if you work on a lock and have radar passing you all day at waist level! - probably end up with fried nutts
I hang around the other side of the kitchen even when the microwave is on! - I sure wouldn't risk a radar scanner at 5 foot away for 2hours (or longer if you're looking to cross the channel or something and you need it)
If you can't mount it a good 1-2 foot above your head at standing on a rib (so a good 7 or 8 feet above sea level), I wouldn't bother - the range and sea clutter would be so poor most of the time crashing around in a rib it would hardly be worth bothering with anyway - not to mention the damage it could do to your health! what i'm swinging at is, I think everyone knows someone who has been effected by some sort of cancer - I think the massive increase in the disease in the last 10 years is due to the amount of electrical devices, phones, antennas and radars that all give off some sort of radiation....It can't be good for us, but because we rely so much on the technology now, theres no going back (says me who is typing this on a wifi laptop with the antenna 10 inches away from my crotch