Radar: Pole or Mast Mount?

[neelie]

KA4WJA - Thanks for your link to the original discussion. This was what I was seeking.

I had not considered the possible increase in sea clutter.

You've sold me - it will stay on the mast.

Merry Christmas.

[rgleason]

We do not seem to have a sea clutter problem with a backstay mount at about 10 - 12'. Perhaps it is attributable to the gimbal which keeps the antenna horizontal. I will readily admit that we will not see kayaks from 8 miles, but they are not the problem. Tankers and fast ferries are and they provide a target well above the water, Hopefully if we cannot pick up a bouy (which has not been a problem) the chartplotter will show it. We have not felt limited by our 20 year old Raymarine Autohelm Radar RL7 except for size of screen and monochrome. Admittedly operation is in fog with little sea often or nightime in good weather. Our coastal use is perfect for the backstay mount.

I have used much more current installations at night in seas with mast mount at 32' and could do mapa on "contacts" 16-18 miles out. Even in seas of 6-8'. That was nice to know and anticipate. The choices get more real at 3-5 miles however, which happened to be when AIS started working, which is a huge help with identification and VHF dialog.

I imagine if or coastal cruiser were to be re purposed with a new radar, and goals more distant, we might want the advantage of picking up local weather with it on the mast, plus the weight of the thing would not be as citical, but the windage would still be an issue with these huge domes. All the excess cruise gear is what slows us up and changes polars.. Anyway I've not noticed problems with sea clutter or missing "contacts" with the backstay mount and I think the gimbal adds effective height as compared to fixed mast mount... don't know how much but it depends on heel.

I guess the two locations are good for different reasons.

Thanks for bringing out the differences.

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[Paul L]

Originally Posted by rgleason

Written some time ago


Our backstay mount radar is on a gimbal 12' above water. The maximum range for a similar height object is
1.22nm x sq root height of radar + 1.2nm x sq root ht of target
1.22nm x sq root of 12' + 1.2nm x sq root of 12'
1.22nm x 3.464 + [/FONT]1.22nm x 3.464
4.22nm + 4.22nm = 8.4nm
Therefore we will only be able to see about 8 nm Miles over the curvature of the earth!
PURCHASING a 24nm or 36 nm RADAR and suffering the added weight (aloft or on the stern), windage due to size, and battery depletion is pure insanity.


I wrote some time ago, the following:

Our backstay mount radar is on a gimbal 12' above water. The maximum range for a similar height object is
1.22nm x sq root height of radar + 1.2nm x sq root ht of target
1.22nm x sq root of 12' + 1.2nm x sq root of 12'
1.22nm x 3.464 + [FONT=Arial]1.22nm x 3.464
4.22nm + 4.22nm = 8.4nm
Therefore we will only be able to see about 8 nm Miles over the curvature of the earth!
PURCHASING a 24nm or 36 nm RADAR and suffering the added weight (aloft or on the stern), windage due to size, and battery depletion is pure insanity.


Sent from my SCH-I545 using Cruisers Sailing Forum mobile app

I don't buy either of these arguments. The difference between a Radar spec'd at 24nm vs 36nm in most cases is increased power and the increased antenna size. The important part is the larger antenna. A 24nm Furuno radar is 2.2kw, 19 in dome. It has a horizontal beam width of 5.2 degs. A 36nm 4kw radar is a 24in dome. It has horizontal beam width 3.9 degs. The lower horizontal beam width (smaller number) gives far better resolution close up and far out. It allows you to distinguish between blobs that combine together vs separate objects. It is somewhat analogous to the pixel resolution in a camera sensor.
With AIS prevalent and so inexpensive (and so low power), I can't see not having an AIS receiver onboard. It is a lot of bang for your buck. Because of AIS we don't use radar to track large ships, close or far off. On most cruising boats you won't be running radar full time offshore, as the power drains are too high. While AIS will be on and consuming very little. We use radar in low visibility situations, AKA fog and heavy rain. We also use it to track squalls. This is better done with 4kw radars, as they tend to punch through the rain giving you a better view of the squall line. We also use the MARPA on the radar to track some boats without AIS, typically fishing trawlers, that are making erratic courses.

The difference in price between a 2kw and 4w radar is low. In the Furuno UHD case it is US$200.

To the OP, I prefer to have the radar on a pole. This keeps the weight out of the rig - a good thing. The long distance radar I use is with squalls and these are seen just as well from a rig mounted vs pole mounted radar. It also reported that very close in imaging is better with a lower radar dome.

[rgleason]

our 20 year old Raymarine radar is listed at 16 nm. Not asking you to "BUY" ANYTHING. THERE
are not absolutes and each boat / sailor is different. Your opinions have been noted however. Glad they work for you.

I agree with much of what you say. We should get Ais. Do you think pole mount is just as good for weather storm front detection?

I like broadband features but not as good for weather. Like low power and quick on off. Have 32 britol so 24" out of the picture.

...but if 4w is available that is smaller that might be ok.

[OldFrog75]

I routinely sail a Beneteau 323 with a 135 genoa and a mast mounted radar.

The genoa hangs up on the radar when tacking. Bad for the sail and really bad for the radar mounts on the mast.

[Randyonr3]

Originally Posted by markpierce

I don't like the idea of my eyes/body scanned by low-mounted radar. Mine is on the mast.

With the area you motor around, and the blank spot, say 10 degrees dead off the rear, I would think you would be afraid of those barges or ships running up and down the river climbing up your tail in the middle of the night..

[markpierce]

That hasn't been an issue, yet, Randy.

[Pete the Cat]

I like my pole mounted radar. The main reason for radar here is to be able to differentiate targets close in, not 16 miles out. Putting the antenna lower helps define very near discrete targets which you will much appreciate if you are going through a narrow, fog entombed passage with traffic or trying to find a narrow opening or buoy. Some of the data here about range presumes that the antenna is at sea level. Obviously, that is not the case.

Please, for you own safety and that of others, do not think that AIS replaces radar if you come to Maine. Most of the small working boats and recreational boats are broadcasting nothing.

[neelie]

I'm the OP.

A close call, but I have decided to stay with the mast mount because:

1) the potential for sea clutter in 10ft seas.
2) the potential large shadow over the solar panels
3) cheaper because existing mounts are on the mast
4) no apparent loss of ultra low range performance.
5) I've succumbed to the herd mentality.

Trust every one had a Merry Christmas.

Cheers

[NorthPacific]

Mine is on a pole. About 15ft above the water. It is a 24 mile radar, 12 years old and works great. In fog and at night it is great. Out at sea I put it on a watch and it scans at a set time.

gps wonderful Ais wonderful. Radar actually sees things that go bump in the night.

As to mast mount. I am sure some can give you the math for the number of pounds on the end of a lever in a seaway at 20, 40 ft. Also the fact that the unit is gyrating so much can be a hindrance.

As to range as I said mine is a maximum 24 miles. My math takes into account that most land falls and vessels stick up from the horizon so that you pick up a target with ample time before going bump.

AIS is not to be scoffed at. However it is not the new wonder drug some would have you believe. Not all vessels run with it on. Mine is receive only. Navy ships and ships not wishing to be monitored. Some times someone does not switch it on or it is mistakenly turned off. Or in crowded waters when every yacht and row boat is transmitting it gets turned off because it is a pain in the arse. Or in many of the offshore cruising grounds few vessels use it and some do not carry lights.

20 years ago most sailors had no electronic aids, now us of the consumer generation are often judged on our seamanship by the number or electronic "stuff" we rely on.

[a64pilot]

One of the best uses I've had for Radar is tracking squalls, for that mounting height is irrelevant. Do head sails have a tendency to chafe on mast mounted Radars?