Radar Arch for CD 25

helm · Posted: Sat Jan 24, 2009 12:42 am Post subject: Radar Arch for CD 25

We are adding a Sitex MDS-9 radome to our CD 25 and think that a radar arch would be the ticket. What do you like about your current arch?
What would you change? If you could have the perfect arch what would it be? Who would you have build it?
Thanks
Eric

thataway · Posted: Sat Jan 24, 2009 12:38 pm Post subject:

One caution is to not make the total height of arch and radar low enough so there is no problem with bridges and trees. Some folks want to put the dinghy under the arch--and this usually requires 15 to 17" off the cabin top. Do you want rocket launchers? Are you going to re-locate the steaming light/riding light to the arch?

We have just gone with short pedistals (made of 4" PVC Pipe" on our C Dory 25 and Tom Cat. The Radar is located far enough foreward, that the dinghy goes aft of the radar, and the aft pontoons go on each side of the radome.

Doryman · Posted: Sat Jan 24, 2009 1:56 pm Post subject:

helm · Posted: Sat Jan 24, 2009 2:56 pm Post subject:

Warren and Bob
Both of you seem to think it best to just mount the radome on the cabin top. Aft or forward?
Thanks
Eric

JamesTXSD · Posted: Sat Jan 24, 2009 3:45 pm Post subject:

Hi Eric,

We have the tall factory arch on our 25. Works great with our dinghy on top. Knowing we'd have the camperback, we didn't want to have the radar at the forward part of the cabin... we put the dinghy on top from the bow and can just slide it straight back. If the radar was on a pedestal towards the front of the cabin, you would have to work around it with the dinghy. Besides the radar, we have our VHF antenna and GPS puck mounted on the arch. To keep things out of the cockpit when we're cruising, we have tied other stuff to the arch while at anchor (solar shower with the hose led into the head, fuel containers, spare anchor, fenders, etc).

Dr. Bob certainly has a point regarding height... I figure we're close to 13' on the trailer and I plan for 12' clearance when on the water. Neither of those has been a significant factor to this point, but it is something to keep in mind.

Hope that helps.

Best wishes,
Jim B.

thataway · Posted: Sat Jan 24, 2009 4:12 pm Post subject:

Warren, I have "shot through" dinghy's for some time. There is little loss of radar image, through the fabric or even wood. There can be some loss if you are shooting through metal, however, many sailboats put the radar dome on the aluminum mast. Again, there is little loss.

We make our Radar high enough to be above the metal of the air conditioner. We use "water closet fittings" on the top and bottom of the PVC pipe and bolt these to the cabin top and a piece of Starboard for the bottom of the radar dome. We have used this technique for over 9 years on various boats. The cost of this "radar mount" is less than $20.

The first photo is the Tom Cat and we have put the dinghy upside down over the air conditioner, radar and hailer at times. The second photo is the C Dory 25 which has only the radar in the center, and we can put the small dinghy aft.

Doryman · Posted: Sat Jan 24, 2009 9:47 pm Post subject:

matt_unique · Posted: Sat Jan 24, 2009 10:19 pm Post subject: Radar

I too suggest mounting the radar up on a pedastal. My preference was to mount it forward. My dinghy fits perfectly between the all around light and the rear of the radar pedastal. On the Tomcat the all around light is aft and would affect the position of the radar mount unless it were otherwise moved.

thataway · Posted: Sun Jan 25, 2009 4:58 pm Post subject:

We bring the dinghy up from the side. One hand on the dinghy and one hand on the cabin railing to steady each of us. Two pulls and the dinghy slides right up onto the cabin top.

journey on · Posted: Mon Jan 26, 2009 3:33 pm Post subject:

Here are a couple of thoughts about a radar arch and installing a radar.

First, the radar on top of your boat sends out the same type of microwave energy as a microwave oven. It seems to me that whatever the circumstances, avoiding that blast of microwaves would be desirable.

In addition, the higher the radar dome, the better one gets data, due to the earth's curvature and sea clutter angle. OK, when it's on a C-Dory, you can't get very high, but to do the best I can, I got the "high" radar arch.

So, once we selected the high arch, where do we put the radar transmitter so as to avoid the most energy? Well, the energy comes out of the antenna at ~+30 deg. So there's a cone of silence (sorry, couldn't resist,) directly below the radar dome. And that's where I mounted the arch and the radar dome. With the anchor light pedestal removed, I also have free access to the cabin top. If you don't want the arch up there, because of fishing pole holders, at least mount the radar dome up at the front.

Boris

thataway · Posted: Mon Jan 26, 2009 6:34 pm Post subject:

The amount of "range" on the radar on the top of a C Dory will not effectively change with the antenna being 2 feet higher. The radar horizon for 12 feet and 14 feet off the water is essentially the same.

The microwave energy of a recreational radar is of very short duration and relitively low power, and the beam is rotating. I suggest that people not put their eyes or genitalia within the beam. Most of us are outside of the 15 degree down cone of the radar (as Boris says the total beam width vertically is about 25 to 30 degrees). Most likely even the head will be out of the beam with the radar mounted on a low bracket on the aft part of the cabin top. As Boris, we mount ours close to the front of the cabin, and we are directly under the scanner, where there should be no danger of microwave radiation. The health risks of a high power military or air port radar is an entirely different story.

journey on · Posted: Mon Jan 26, 2009 8:13 pm Post subject:

When one reads this, one may assume that I don't have much to do today. You're correct. Company left. Next company due Friday.

Bob's correct as to range. Assuming that a C-Dory Cap'n is only interested in reasonable sized targets on the horizon (25' or greater,) the difference in range is <1/4 mile (actually 10.60 vs 10.76 for those that are picky.) And it probably doesn't give much of a better look angle at short range (sea clutter,) wave reflections.

Where I worry more than Bob is the cumulative effect of microwave radiation on humans, especially the thinking area (no, not that part, higher up around your head.) Having spent a lot of time around microwave transmissions, I tend to worry that the damage is cumulative, and thus will do anything to minimize it. 2' higher above my head sounds better than 1/2' to me. And 2 Kw is not a trivial amount of power.

And the arch leaves the cabin top clear, front or rear.

Fried Boris

lloyds · Posted: Tue Jan 27, 2009 11:16 am Post subject:

There used to be a fishing guide on the lower willamette river who fished a alumaweld guide model, about a 22 footer with an outboard. He had radar mounted on about a 2 foot post right on his flat bow. It was right at head height for he and his clients if they were sitting in the chairs. His nickname was "radar". Everytime I saw him on that boat I wondered how his faculties were doing, and those of his clients.