Radar Beam - cooking zone

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I have been thing about radar (Garmin 18 HD) placement a lot lately for my 22 cruiser. I am trying to do all the electronics install myself and that, combined with the lower profile, had me thinking about the direct to cabin top, forward install.

My understanding of the radar is the beam spins 360 degrees and the danger zone is 12.5 degrees below and above the horizontal.

So if that is true, and looking at pics of 22 cruisers with this install, a person in the aft dinette seat and someone in the cockpit are directly in the danger zone. If this is true it may be fine for single handers and couples cruising , but not for fishermen fishing in the fog.

Does my thinking make sense or am I missing something?

Oh, and Merry Christmas!
 
This was discussed back in November at : http://www.c-brats.com/viewtopic.php?p=251471

Generally if you put the radar up a little, you will be perfectly safe. The amount of radiation to a person is minimal with the modern radars. The most vulnerable part of the body are eyes (cataracts) and gonads. The radar pulse is very fast and since the scanner turns in the dome at either 24 or 30 RPM, the horizontal beam width of 5 degrees, is only hitting any object for a short period of time. The amount of energy at 10 feet is 1/100th of the amount of energy at one foot.

If the radar center of the beam were flush with the top of the boat (which it is not), at 6', the lower edge of the beam would be 1.33 feet below the top of the boat--and that would clear most people;s head entirely in the seat.
Lets go back to 12 feet, and there your beam is 2.66 feet below the top of the radome, but the energy is less than 1/100th at the dome, even though their heads may be in the beam.

Normally the radar is mounted with a down slope of 4 degrees, and this brings the beam at the aft point to be only 8.5 degrees. With this assumption and also that the people would be about 10 feet in back of the beam the beam would be 1.49' below the top of the roof.

To be entirely safe you can mount the radar 1 foot off the roof, with a 4* wedge--as most of us do, and all heads should be clear, or at the very bottom of the beam--and there should be minimal if any risk.

I don't know how far foreword you are going, but there is a down slope on the forward part of the top. I have put my radars just in back of that downward slope, which is in back of the helm position. This also decreases the chance of radar hitting the person. Even if you go flush, the beam center starts at about 6" off the top of the cabin.

I don't know if you have looked at what has been referred as the commode mount: Using household water closet PVC pipe fittings. This is simple, cheap and can be any height you want.

IMG_0558.sized.jpg
 
thanks Dr Bob,

I think I will go on 5" pedestal at the back of the cabin top then I can put the dingy on top, and rout the wiring along the top of the windows.

How did you do the flanges on your PVC mount?


Stefan
 
The flanges are standard water closet mounts from Home Depot. As I recollect the PVC pipe is standard 3" for the inside of the flanges or 4" for the outside. We have made all of these out of 3" pipe. There are several negatives for the flanges and pipe, but these can be remedied. We are now filling the other holes in the flanges with epoxy and fairing, then painting all of it with "Fusion" for Plastic by Krylon spray paint. This seems to last well. We did the first one of these about 8 years ago, and it is still in use on a trawler which did the loop and has been to the Bahamas several times.

We made the platform for the radar out of Starboard (or other High Density Polyethylene plastic. You can easily put a second piece and use a belt sander to make the 4* wedge.

Just be sure that the dinghy does not have an aluminum piece to re-enforce the transom for the outboard. The radars don't shoot well thru this. If you have this, then raise the radar above this. There are several options for the Radar cable--but along the inside of the top of window is one of the best.
 
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