Mast mounting radar

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Gluing hardware

Postby Michel » Fri Jul 10, 2009 6:43 pm

Gluing hardware to CF spars, that's interesting; we don't hear much about that here....can you enlighten us a bit, David?
Michel Capel, Freedom 44 #4 1981 'Alabama Queen', NED8188, cat ketch with wishbones, home port Enkhuizen, the Netherlands, 52*42.238'N 005*18.154'E.
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Re: Mast mounting radar

Postby Mike Holibar » Sat Sep 05, 2009 5:09 am

Hi guys, I hope your summer season is going well and you are getting in some sea time!
I note Geoffs comment re blind spot on Fyne Spirit and others wondering about radar performance around CF masts. Last summer sailing down the coast we had a contact/target astern and there did not appear to be much of a blind spot if any, perhaps 5 deg each side of the course line. On the other hand there appears to be a more noticeable blind spot of 4 or 5 degrees each way due to the fore mast. I wonder if the "rear view" is due to the scanner being of greater diameter than the mast, and the tip of it being able to transmit and receive effectively eventhough the mid part would be blocked by the mast.

Regards,
Mike Holibar
S/V Fyne Spirit of Plymouth (Freedom 39PHS-1989)
Lyttelton
New Zealand
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Re: Mast mounting radar

Postby Michel » Sat Sep 05, 2009 6:03 am

That could be the case. But we're becoming increasingly aware that CF masts do not reflect radar. One Freedom owner made a trip to Bermuda and was not noticed by the powerful on shore radar of the harbour authorities. He did not have his reflector up, I think. As yet, it's unclear what happens with radar beams transmitted from a scanner mounted close to the CF mast. It does not sound logical that CF does not reflect radar sent from afar and does reflect radar sent from close by. Anyone having more shreds of evidence in this discussion: please come in!

To start with, found this abstract of an article in the Journal of industrial textiles:
Investigation on the Radar Absorption Properties of Carbon Fiber Containing Nonwovens
Hua Zhu

College of Textiles, Donghua University Shanghai 200051, PR China, xbfyzhuhua@163

Jianchun Zhang

The Quartermaster Research Institute of General Logistics Department of the CPLA Beijing 100088, PR China

Pïng Chen

Department of Electronics Science and Technology Nanjing University, Nanjing 210093, PR China

Xiangcheng Wang

Institute of Chemical Defense Beijing 102205, PR China

Nonwovens containing pitch-based carbon fiber (PCF), polyester fiber, or wool fiber with thermo-bonding fiber 4080 as the bonding agent are fabricated by the through-air thermal bonding process. The volume fraction of carbon fiber in the nonwovens ranges from 0 to 1.5%. Radar wave absorbing properties of the nonwovens are investigated by the far-field RCS measurement in the frequency range from 8 to 18 GHz. Results of the measurement indicate that the radar-absorbing capacity of the nonwovens is closely related to the volume fraction of carbon fiber in the nonwovens and the thickness of the nonwovens, regardless of the types of fiber except PCF in the nonwovens. When the thickness of the nonwovens is 10 mm, radar-absorbing capacity of the nonwovens varies with the content of PCF and reaches the maximum around the PCF volume fraction of 0.036%. When the thickness of the nonwoven with the PCF volume fraction of 0.036% is 6 mm, there appears an absorption peak on the curve of reflectivity at the frequency around 11 GHz, and the absorption in the whole frequency range from 8 to 18 GHz is intensified. Electromagnetic parameters of the component fibers in the nonwovens are tested by the coaxial transmission line method andthe radar absorption characteristics of the nonwovens are explained on the basis of the electromagnetic properties of these fibers.

Key Words: pitch-based carbon fiber • nonwoven • radar absorption • reflectivity • electromagnetic parameters.

Journal of Industrial Textiles, Vol. 37, No. 1, 91-105 (2007)
DOI: 10.1177/1528083707078125

======================================================
Note the mention of an absorbsion peak at 11 Ghz, in the middle of the X-band radar frequency range (8-12 Ghz).


This is what I found on Wikipedia:

Radar Reflection

Electromagnetic waves reflect (scatter) from any large change in the dielectric or diamagnetic constants. This means that a solid object in air or a vacuum, or other significant change in atomic density between the object and what is surrounding it, will usually scatter radar (radio) waves. This is particularly true for electrically conductive materials, such as metal and carbon fiber, making radar particularly well suited to the detection of aircraft and ships. Radar absorbing material, containing resistive and sometimes magnetic substances, is used on military vehicles to reduce radar reflection. This is the radio equivalent of painting something a dark color.

======================================================
Here it says that CF gives a good radar reflection; this is contrary to our believes.
Michel Capel, Freedom 44 #4 1981 'Alabama Queen', NED8188, cat ketch with wishbones, home port Enkhuizen, the Netherlands, 52*42.238'N 005*18.154'E.
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Re: Mast mounting radar

Postby Cloud 9 » Sun Jan 10, 2010 5:27 pm

Hi All, Sorry it took so long to get this posted. I ended up having a machine shop fabricate a clamp type mount. No holes neccessary and it has withstood 100+ mph winds here in the FL Keys. Yes it's overbuilt, but I did not want this thing going anywhere. It weighs 20lbs and made from stainless steel. I used an adhesive conduit from Home Depot to run the wires down the outside of the spar to the display.
Attachments
radar front.jpg
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radar distant.jpg
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radar aft.jpg
radar aft.jpg (48.17 KiB) Viewed 3604 times
Last edited by Cloud 9 on Mon Jun 22, 2015 10:16 pm, edited 1 time in total.
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Re: Mast mounting radar

Postby captb » Mon Jan 11, 2010 4:48 pm

greetings from Tampa..
I will be putting radar on my Freedom 40 cat/ketch in a few years...
do you have a picture or specs on building it..
i do have an excellent machine shop here in St.Pete...owner is also a sailor, etc..
thanks..
Capt. Herman
come sail anytime... :!:
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Re: Mast mounting radar

Postby Cloud 9 » Mon Jan 11, 2010 6:11 pm

I received an inquiry as to it's height off the deck etc. So I'm posting it here for everyone. It's on my Freedom 35 (sloop rig) 19' off the deck. So it's about 23' above the water. When determining the height to mount it I raised the jib in zero wind and looked for the widest point between the leech and mast. This was done to cause the least interference when tacking and so far no problems. I also allowed an extra 1/8" inch of space in the diameter to allow for a rubber gasket to go between the mast and the mount. I didn't want any "hard" compression between the mount and mast. I felt this would relieve unneccessary stress. I was concerned if it was too tight the mast would snap right above the mount. I've included a full size photo below. In the photos you will notice there are three bolts on the front which compress the two halves together. Thus, the amount of compression is adjustable. I was in a big hurry to get it mounted and head south so I haven't had time to go back up and trim the excess rubber padding to make it look all neat and tidy.
The mount is a one of a kind. I just sketched a design and gave the dimensions to the shop and they fabricated it for me. If I had drawings it wouldn't be much use unless you were mounting it on a freedom 35 due to varying mast diameters. It does have enough "play" in it where I could move it up or down the rig at least 12-20 inches.

The back of the dome is roughly four inches from the spar and did not experience any blind spots. Even the best autopilot will not steer you in a perfectly straight line so blind spots are not an issue. One last note: you will notice a small horizontal plate along the front and bottom of the mount. This was added so I can mount a foredeck light in the future.
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deja vu.jpg
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Last edited by Cloud 9 on Mon Jun 22, 2015 10:17 pm, edited 1 time in total.
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Re: Mast mounting radar

Postby seadago » Tue Apr 09, 2013 5:49 pm

Hi, I'm also thinking possible mountings for a radome. I have a Hoyt 30 cat ketch with (at the moment) wraparound sails, so mounting anything on the mast, either mast, is not an option. Have looked at setups on a transom pole but they look somewhat awkward and in the way of too many other things aft. Did anywone think of a stand-alone pole mounting forward of the main? I though about the interference of the masts but when it comes to compromises, I'd rather have good viz of what lies ahead instead of behind me. Any ideas wellcome! Thanks
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Re: Mast mounting radar

Postby 1980raven » Tue Apr 09, 2013 9:43 pm

I have a f28CK with wrap around sails. I think that mounted on a freestanding pole in front of the mast is a great idea. Since i have not had Raven (my first sailboat) in the water yet; I am not sure how the radar would survive in a pounding sea. Maybe someone with more experience will weigh in.
Freedom 28 CK Hull# 14, centerboard, wrap around sails with WB booms
Narragansett Bay, RI
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Re: Mast mounting radar

Postby Freespirit » Wed Apr 10, 2013 9:37 pm

My boat came with a small radome mounted atop a stern mounted pole.
I chopped the pad off of the top and added an extension, leveling unit and a cross arm for the antennas.
Plus it gave me mini spreaders to hoist flags.
Image


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Chuck & Lauri
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Freedom 42 Hull #1
Somewhere in the Pacific
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