Being from Maine and cruising from Maine to Canada I find this statement from Raymarine rather ridiculous.
I have had radar mounted on the mast, a Questus back stay mount and a pole. I currently have it on a pole and HATE IT for performance reasons. Even when I had it on the mast, on three other boats I've owned, I could pick up my boat neighbors in the mooring field with no problems.
Even in Maine, where fog was invented, I have yet to find more than 4 or so days out of the last 20+ years where the visibility was less than 75 feet. If you have not acquired a target by the time it gets that close you're just not doing your job.
As someone who has spent literally thousands of hours operating radar in the fog, as both a commercial fisherman and a pleasure boater, there is NO question that a mast mount, 22-25 feet up, would be my preferred placement. Eventually I will remove my pole and place my dome on the mast but the boat came this way and the radar pole has been painted around with Awlgrip. I clench my teeth every time I am in 6+ foot swells, and fog, and keep loosing targets and having to re-aquire them due to the low dome height when in a trough. I rarely if ever had this problem with domes mounted on the mast.
If you only sail in protected foggy bays with no swell or chance of a sea a pole mount can suffice but if you venture into the open ocean, at night, or in the fog, a higher dome placement will track and keep targets on screen far better.
It's not all just about radar either.....
Things to do when in fog to be a good boater and to be courteous to others.
= BUY ONE AND USE IT!!!! Just because you choose not to have radar does not mean you should choose to be invisible or nearly invisible to the rest of the world who may be practicing good collision avoidance.
= USE IT and by that I mean turn the darn thing on and monitor VHF 16. PLEASE! The rest of us don't have your cell number on speed dial. "Vessel rounding 2KR what are your intentions, over?........." Silence..........=dumb
= When the visibility drops USE THEM! They do help and can add another 50-100 feet of warning.
= For Christ sake Wal*Mart sells sports air horns for $6.00. Please get one and use it properly.
Slow Down =
A single sailboat traveling at 6 knots is covering 10.1 feet per second. In 100 feet of visibility the collision time to a fixed object is roughly 11 seconds from your first physical sighting. Of course you should have aquired this target LONG before 100 feet!! Now take two sailboats converging, each traveling at 6 knots, your collision time in 100 feet of visibility, from your first physical sighting, becomes just 5 seconds. You had better aquire your targets LONG before the stated by Raymarine "close in performance" even matters or you'll be in a heap of trouble..
A power boat traveling 30 knots, on a collision course, will collide with a sailboat doing six knots, at 100 feet of visibility, in under two seconds from the first sighting! You will NOT have enough reaction time to avoid a collision with a clown like this other than to have radar and been tracking him far ahead of the "close in performance". Think people don't go fast in the fog? Think again..
Some photo examples of what these reckless boaters look like:
There really is a boat here 200+ feet off my stern. No radar, no reflector, no running lights, no horn signals and not even a VHF response. "Dumb dee dumb, sailing awayyyy, dumb dee dumb, doh', a boat, how'd that get there?"
Here's a radar shot of that boat when it was actually showing up. It's the red spec just above the 18 foot spot off my stbd stern quarter. The two targets ahead and to port and stbd were two J Boats traveling together both of which had reflectors when they went by. SOME BOATS JUST DO NOT SHOW UP ON RADAR!!! The guy behind me owns one!
1st class clown (see speed above), no radar, no lights, no horn signals, no reflector and also not showing up well, and not monitoring VHF!
For reference this is 400 feet of visibility from a few weeks ago (400 feet is generally fairly decent vis for Maine fog):
And here's the screen shot with the cursor just over the closest radar image at 411 feet (upper left corner measures distance).:
It scares me how many people are just plain dangerous and have no clue they are being so reckless. If they succeed once they do it again only this time with a greater level of comfort and confidence.
So in summary I'd still opt for mounting the dome on the mast..