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Old 12-06-2011, 07:31   #1
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Where to Mount Radar ?

I'm thinking of adding radar, and wondering where to mount the radome: on the mast, or on a pole coming up from the transom. I worry about drilling holes in the mast (weakens it?) and adding that weight up there, although it would be cheaper. The pole seems like I could make it super solid but does the mast interfere with the radar image? Any thoughts?
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Old 12-06-2011, 07:42   #2
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Re: Where to mount radar?

high up and gimballed
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Old 12-06-2011, 08:09   #3
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Re: Where to mount radar?

I have had mine mounted on the transom for 20+ years. Very simple manual gimbal arrangement for when on a tack works well. Also easier to maintain standing on the stern pulpit instead of going up and down the mast. Range is less than on the mast-usual rough estimate of horizon is sqrt(h) nm, where h is the radome height in feet. And you add the height of the target to get the total range capability. So at 25 ft vs 10 ft you get 5nm vs 3.1 nm. I rarely use the longer ranges, occasional large ship search has been replaced by AIS, and 3nm or less is most of the time. And you don't see the mast with conventional pulsed radar-it is in the blind zone (you can't receive while transmitting, so cant see anything within a pulsewidth of the transmitter).
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Old 12-06-2011, 08:33   #4
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Re: Where to mount radar?

This is where I put mine. Having it higher up only increases range a very small amount, and the extra windage and weight aloft make for more hobbyhorsing. I wouldn't go higher!

M.

BTW. In monohulls, ONE more pound at the top of the mast, requires 100 MORE pounds on the bottom of the keel, to counteract it! The "range advantage" of higher up, is only about 10%. IMO... It's not the ship at 20 miles that matters, it's the one at 3!
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Old 12-06-2011, 08:38   #5
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Re: Where to mount radar?

Quote:
Originally Posted by chrisferro View Post
I'm thinking of adding radar, and wondering where to mount the radome: on the mast, or on a pole coming up from the transom. I worry about drilling holes in the mast (weakens it?) and adding that weight up there, although it would be cheaper. The pole seems like I could make it super solid but does the mast interfere with the radar image? Any thoughts?
1) If you're planning on using the radar on blue water passages for collision warning and to detect weather, mount it high up on the mast for maximum range. If you want to use it for coastal sailing in reduced visibility, you can mount it lower down, on a lollipop pole or backstay.
2) Gimbal mounts get mixed reviews. Most people feel the cost/benefit ratio is too high. I have a Questus backstay gimbal mount, but only because I got a very good deal on a second hand unit with a radar thrown into the deal. While I'm happy with it, I don't think I would get it if I had to pay the normal price.
3) Since the cross section of the mast is probably much smaller than the antenna array, you should not expect much shadowing dead ahead.
4) The whole radome assembly for a small boat radar is going to be pretty light (~20 lbs). Unless you mount it really high up the weight should not be a problem. Position it so the radar mount and cable pass-through holes don't line up with any existing holes and it will be fine. Make sure that you have a guard rail around the base of the radome to protect it from getting whacked by your genoa.
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Old 12-06-2011, 08:38   #6
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Re: Where to mount radar?

The height of radar depends on the type of cruising you do. I moved mine from a pole on the stern higher up on the mast to expand range. I was also concerned about the health hazards of radar waves being too close to crew.

If you search the archives, you'll find a lot of discussion on this topic.
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Old 12-06-2011, 09:00   #7
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Re: Where to mount radar?

It comes down to the hassle of mounting it on the mast, windage and the potential of snagging things versus mounting it on transom and having less range.

The difference in range a ship can move in a matter of a few minutes plus the majority of ships now have an AIS transceiver. I am not saying to rely solely on AIS.

I would opt for the transom.
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Old 12-06-2011, 09:04   #8
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Re: Where to mount radar?

transom mount is difficult with a ketch---if you have a sloop, transom mount only makes brain fry a little...... mine is a ketch--is up mast and i dont fly a yankee......no problem ...
windage?? my radome is tiny and i dont care if there is windage--i have also freeboard, which many dislike, but helps with pooping seas...LOL
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Old 12-06-2011, 09:47   #9
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Re: Where to mount radar?

BTW, as far as shadowing, don't forget that the mast mount does increase blockage for targets approaching from astern. But even that is less important as you yaw a bit and the giant freighter gets close enough to honk at you. Go AIS!
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Old 12-06-2011, 09:50   #10
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Re: Where to mount radar?

Quote:
Originally Posted by sded View Post
BTW, as far as shadowing, don't forget that the mast mount does increase blockage for targets approaching from astern. But even that is less important as you yaw a bit and the giant freighter gets close enough to honk at you. Go AIS!
i have wooden masts--shouldnt be such an issue on mine.....so i have been advised.....and ais is part of my garmin should i ever feel like hooking it up..
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Old 12-06-2011, 10:34   #11
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Re: Where to mount radar?

One advantage in the higher mast mount is reduced blockage from big seas, especially when the boat is heeled significantly. Also at times it is good to be able to "see over" nearby obstacles such as river banks or wharfs.

And as to the above quoted " one pound at masthead equals 100 pounds in the keel"... I think there is one too many zeros in that ratio since typically the mast height is on the order of 10 times the depth of the keel ballast. One should of course minimize weight aloft, but as well one should minimize weight in the ends of the boat, so adding a mast and radar at the extreme stern is not without penalty.

There is no free lunch...

I have had both mast and stern mount, and overall I prefer the mid-mast position.

Cheers,

Jim
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Old 12-06-2011, 10:51   #12
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Re: Where to mount radar?

I have a Furuno half way up a 72' mast and a Northstar on a stout stern pole; have used both extensively.

No mast nor boom shadow on stern mount; much easier to service.
Much better range on mast mount.

Also very important.... where to mount the screen.
Mounted the first screen back at the helm; nice to have when helming but a PIA when the autopilot is steering and you are sitting in the front of the cockpit. Think you see something at night and you have to crawl around the helm to look at radar. Answer was to mount the second screen up under the pilothouse (would be front of dodger in foreward portion of cockpit in most boats) so you can see it from where you sit on watch with autopilot on.

Think about where you spend most time on watch and mount radar screen accordingly; we are usually not at helm if autopilot is on.

Fair winds,
Dr. Michele
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Old 12-06-2011, 11:52   #13
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Re: Where to mount radar?

Another option is pole/back stay mounted.
This takes a bit more care in the fabrication since the back-stay moves quite a bit...a flexible mount at the base is necessary.

One nice thing about this installation, that is shared with a stern pole, is the possibility to add horns and and install GPS, sat phone and other antennas.
I also put a light under mine...its real nice for lighting the aft deck.
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Old 12-06-2011, 12:09   #14
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Re: Where to mount radar?

Mine is at the first spreader from the deck. About 22 ft. off the water. This is where the PO installed it and when I put a new one up, I used the same mount. It is not gimballed, but then my motorsailer doesn't heel that much under sail. As for maintenance, it is very easily accessed with steps or bosun chair. Having said that, in the 25 plus years I have used radars I have never had to do anything to the radar dome except when changing it for a newer model.
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Old 12-06-2011, 12:34   #15
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Re: Where to mount radar?

Not sure the gimbal is worth the trouble. Mine have been about 20 feet up the mast. That got me plenty of time seeing freighters pretty far out. Always worked fine without the gimbal. Really just a matter of how far you want to see....
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