Mast mounting radar

Batteries, Generators, Solar, Wind and Electronics
Cloud 9
Posts: 11
Joined: Tue Jul 07, 2009 8:51 am

Mast mounting radar

Post by Cloud 9 »

Even though my Freedom 35 has a radar arch on the transom I'm considering mounting the radome on the mast about 10 feet off the deck. I know drilling holes are a big no-no so I'm designing a clamp on type mount which would require no holes. I'm buying the NorthStar broadband so radiation is not an issue and the cabling is a much smaller diameter than your typical radar (cat5 and 4 small wires) and will try an external conduit. If anyone has any suggestions or reccomendations I'd appreciate it.
Thanks, Gordon

Mike Holibar
Posts: 174
Joined: Mon Jun 01, 2009 12:41 am

Re: Mast mounting radar

Post by Mike Holibar »

Gordon,
Fyne Spirit has the radome screwed to the mast with an internal conduit leading the cable below. I too have picked up the message about being very cautious as regards drilling any holes in the mast and no doubt one of the very learned members on this site will correct me if I am wrong in expressing the following opinion. And that is that the higher up the mast you are working, the less localised stress there will be that could be aggravated by a hole. The working compression and tension loads must diminish with height. To take it to an extreme, ten holes 1 metre from the top of the mast would be unlikely to cause it to fall down, but the same holes near the bottom could be disastrous. My radome is about 6 metres off the deck.
Attachments
fs cove.JPG
fs cove.JPG (14.95 KiB) Viewed 19931 times
Mike Holibar
S/V Fyne Spirit of Plymouth (Freedom 39PHS-1989)
Lyttelton
New Zealand

User avatar
Michel
Posts: 546
Joined: Sun Dec 07, 2008 5:48 am
Location: Zaanstad, the Netherlands, EU

Re: Mast mounting radar

Post by Michel »

Gordon,

Drilling in CF is i.m.h.o. not such a problem as sometimes thought.

Here's how my radar is mounted on my mizzen with a standard Edson mast mount:
http://www.flickr.com/photos/alabama_queen/282285817/

It's been there with sustained winds of 70 knots. My radar is also about 6 meters / 20' up the mast, like Mike's.

The only caveat when attaching hardware on carbon fibre (CF) is never ever to use self tapping screws; they pry open the brittle CF laminate. Drill and tap thread and use locktite liberally. Or better, use large stainless rivets, but then you have a hard time removing the riveted piece of hardware lateron. If you use rivets, the securing 'blob' should be totally inside the mast, so measure the thickness of the laminate through the holes you use and take long enough rivets.

Good luck and don't be scared to make a few holes.
Last edited by Michel on Sat Jul 11, 2009 9:21 am, edited 1 time in total.
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.

User avatar
GeoffSchultz
Posts: 1135
Joined: Thu Dec 04, 2008 8:39 am
Location: BlueJacket: Guatemala
Contact:

Re: Mast mounting radar

Post by GeoffSchultz »

Gordon,

I don't have an answer regarding mounting the radome, but I will make a comment on NorthStar. I've owned 3 NorthStar units (951xd, 961x and now a 6100i). I must say that I am quite disappointed with the 6100i. The 961x, which I bought about 9 years ago had much more functionality and a better user interface than then 6100i has. I purchased the 6100i several years ago to act as a backup for a RayMarine C-80. Since then they've only come out with 2 software updates, none of which has added any real functionality. I was quite disappointed with this, as this was quite different from my experience with the 961.

Due to the fact that I was a very early adopter of the 961, I got to know the software and repair staff very well. One of the things that I learned was that they don't have common software code bases for their units, and as a result they don't share desirable features.

For example, when I bought the 6100i, AIS was just appearing in the consumer market. The 6100i has 2 NMEA interfaces, one of which runs at 38,400 bps, which is the data rate for AIS. I just assumed that they would implement AIS as the 6100i was their new flagship product. Did they ever do it? No!

I've found RayMarine much better for upgrading their older units with new functionality. Just be sure that the functionality of the Northstar has everything that you might want or need in the future, as what you see is probably all that you're going to get.

-- Geoff
BlueJacket
1997 Freedom 40/40
http://www.GeoffSchultz.org

AlanK
Posts: 127
Joined: Wed Dec 10, 2008 6:59 pm
Location: Freedom 33 Boston, MA USA

Re: Mast mounting radar

Post by AlanK »

My radome is on a standard edson mount riveted to my mizzen mast about 15 feet above the deck. Its taken a pounding at sea and their are no signs of stress cracks or movement there or at any other holes in the mast or the various attachment points (mast track rivets, gooseneck etc.).

Alan F-33 Hull # 51

User avatar
GeoffSchultz
Posts: 1135
Joined: Thu Dec 04, 2008 8:39 am
Location: BlueJacket: Guatemala
Contact:

Re: Mast mounting radar

Post by GeoffSchultz »

Before I get into a side conversation regarding my radar mounting issues, I'll ask a question regarding the proposed mounting location: To me it appears that mounting a radar in front of the typical Freedom carbon fiber mast will cause you to loose radar view of a relatively large angle behind the boat due to the mast blocking the radar beam. How wide is this angle and is this acceptable to you? I know that I can definitely see the radar shadow of the 3" pole behind my radar as well as the mast shadow, which is ~20' forward.

Now onto my own radar mounting conundrums...

This topic is actually something that I've been struggling with for several years. I think that it was back in 2005 that I purchased a Questus self leveling (gimbaled) radar mount and moved the radar from the "normal" mounting location which is on a radar pole on the stern of the boat. Here's a picture of a typical 40/40 setup:

Image

I machined a mount for the Questus which attached to the normal radar mounting plate and allowed it to rotate. However, this setup caused the radar to be dropped about 12-15". Here's a photo of the current setup:

Image

The problem is that on certain points of sail when the boom rises up, it blocks the radar's horizon. I may have had this problem all of along, but this setup certainly exacerbates the problem. So, the question is how to solve this. The problem is complicated by all of the antennas (Wifi, Sirius, 3 active + 1 spare GPS) which I also have mounted on the arch above the radar:

Image

At this point my thought is to chop off the top plate and install an extension tube which would be about 18" higher. I would bring an arm forward to which the Questus mount would attach. I'd also remove the current antenna arch and replace it with an arch which would mount on the Questus directly above the radar, keeping the antennas out of the radar beam. Alternately I could just have another arch built that attaches to the main pole, which would keep the weight off of the Questus. Any suggestions on this would be greatly appreciated, as I've struggled with this for years, and now that I'm home, I plan to solve it.

-- Geoff
BlueJacket
1997 Freedom 40/40
http://www.GeoffSchultz.org

User avatar
Michel
Posts: 546
Joined: Sun Dec 07, 2008 5:48 am
Location: Zaanstad, the Netherlands, EU

Re: Mast mounting radar -> Article from YM

Post by Michel »

Raydome mounting


In the May 2006 issue of Yachting Monthly, a reader's question about the position of a raydome is answered in brief by one of YM's panel of experts. Here is the full version of that question and answer.


I'm looking for some advice regarding where to fit a raydome on my yacht (an X-382). I'm planning to fit a Raymarine C series with an 18"
raydome and would like to mount it on the mast of my X-382. Due to the configuration of the rig - triple spreader with a baby stay and high pole uphaul - the lowest point on the front of the mast where it could be mounted without interfering with the rigging is at the level of the second spreaders, about 12 metres up. I'm not keen to put it that high because of the obvious problems associated with putting that much weight at that height and the amount the scanner will move around in even the slightest swell. I'm also not keen on putting a pole on the pushpit.
I have seen some people who mount their radar scanners on the side of their mast. Doing that would allow me to mount the scanner much lower, at around the level of the first spreaders. I would obviously expect some loss of performance on the side that the scanner was looking through the mast. I would be prepared to accept some loss but I don't want to mount the raydome and then discover that I can't see a thing. Any advice? Richard Clark, via email


Jason Sidaway, Raymarine's Senior Product Support Engineer Radome Scanner Installation replies: Mounting of the radome scanner on the mast is very popular and very much typical for yacht installations for 2 main reasons: 1) safety and 2) range, but there are important considerations to take in account when mounting the radome scanner on the mast.
In terms of safety, this offers an ideal location as the transmitter is well above head height avoiding mechanical danger (not so much for a radome scanner as it is enclosed) and electromagnetic contact removing the potential for compromising personal health on-board when the radar system is operated for long periods and minimising exposure to the crew.
With respect to range of the radar system, since radar basically operates at line-of-sight, the suggestion of higher the mounting position, the longer the range performance, but this is not always the case, remembering that a yacht will be moving and the boat will be 'heeling' . Therefore the radar antenna will be as well. Increased height will offer improved long-range performance but at the same time, increases the minimum short-range detection circle as well as exaggerate any rolling or pitching motion of the vessel.
Therefore, a compromise as such is necessary in attempt to mount the radar scanner as high as possible but take into consideration, the movement of the vessel... A simple equation can be used to calculate the distance to the radar horizon which is approximately 1.2 times the square root of the height of the scanner. For example, a scanner mounted 20' above the water-line will provide the radar of 5.4 miles range before the radar beam is 'blocked' by the earth's curvature.
Immediately, you may say this is contrary to the marketed maximum range scale of the radar but there are two factors to take into consideration with regards to radar range: 1) height of the antenna and 2) height of the target, so the same equation can used to determine the targets radar horizon, by using the sum of the distance to the targets radar horizon to the maximum radar horizon to derive the maximum detection range for that target.
So same example, a scanner mounted 20' above the water-line will provide the radar of 5.4 miles range, radiating a target that is 20' feet tall, can detect that target at a maximum range of 10.8 miles, also remembering that atmospheric and weather conditions can either increase/decrease the range.
The specified maximum range of a radar antenna is determined solely by the ability for the radar system to transmit a pulse to a maximum range and detect a returning echo, the specified maximum range can be compromised and affected by antenna height, target height, weather, horizon etc etc
As already mentioned the main problem for sailboat installations for radar is 'heeling', all Raymarine radar products have a vertical beamwidth of 25 degrees, meaning that 12.5 degrees of the beam is directed downward toward the water and 12.5 degrees directed upward with the centre aimed at the horizon. If the boat is heeling in excess of 12.5 degrees port or starboard, the lower beam will be directed above the horizon and essentially rendering the radar blind in that direction. Additionally, all of the radar energy will be directed into the water, resulting in increased sea clutter... from this aspect, you will heed the benefit a 'gimbal' style mast mounting, which will abolish this problem, maintaining the radar antenna parallel to the waterline.
Another factor to take into consideration is 'blind spots' which can be evolved as a result of detection of masts and booms, if the antenna is mast-mounted, the radar will block the sight of the radar in the direction of the mast, on a typical mast mounted installation, the radar can be subjected to a blind spot of 1 to 15 degrees wide (this is obviously unavoidable) depending on the mast thickness. However, because this is directly astern, it is relatively of lower concern to the user, as generally the higher risk is forward, port and starboard of the vessel. This is potentially where a backstay installation is preferred with 'some' distance between the antenna and the mast, there will be a small blind spot in the direction of the mast.
Additionally, this is also a reason why 'some' scanner installations are located aside of the mast on the spreaders as a combination of the movement of the vessel and the intelligent software used within the Raymarine radar products, it is very unlikely to detect a blind spot visually on the radar display.
Therefore, personal view is that a radar antenna mounted on the backstay using a gimballed mounting is the best choice for a sailboat, although you will sacrifice range performance by mounting the antenna lower and at the same time increasing short range detection, and you will minimise the probability of blind spots BUT remembering the safety aspect with an antenna mounted overhead.
Typically, a radome scanner when mast mounted will be installed on the forward facing of the mast and in some cases, is protected using a radar guard to prevent the sails and rigging from 'hitting' or 'snagging' on the radome scanner.
With the cable run, a high number of sailboats are removed from the water and the mast is 'stepped'.It is recommended that the cable is passed through a waterproof deck gland and a suitable junction is applied to the cable using a suitable waterproof junction box, located inside the boat.

CONCLUSION: the preferred mounting would be on the cross-trees as initially suggested by the customer, offsetting the antenna on the cross-trees should not present a hindrance to the performance of the radar system; in terms of mounting the scanner to the mast, Raymarine do supply a standard mast mounting bracket which would not facilitate the required mounting, suggestion would be to contact Scanstrut (www.scanstrut.com) for recommended mounting solutions but the probability is that a purpose-fabricated bracket will be necessary.




Yachting Monthly, 12 April 2006
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.

User avatar
Michel
Posts: 546
Joined: Sun Dec 07, 2008 5:48 am
Location: Zaanstad, the Netherlands, EU

Re: Mast mounting radar

Post by Michel »

Geoff,

I always heard that carbon fiber masts give no radar echo. So would they produce a blind spot?
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.

User avatar
GeoffSchultz
Posts: 1135
Joined: Thu Dec 04, 2008 8:39 am
Location: BlueJacket: Guatemala
Contact:

Re: Mast mounting radar

Post by GeoffSchultz »

Michel,

Based upon my observations, I assert that carbon fiber masts are not transparent to radar and I will also assert that on carbon fiber masts are larger than aluminum masts, making the radar shadow area much larger. I will agree that they don't reflect radar, but that doesn't mean transparent.

When I look at the photo that Mike posted, it looks like that diameter of the mast is about 2/3 the diameter of the radome. If the dome were in contact with the mast, I think that's about a 60 degree blank spot (please correct my off the cuff math). To me that's way too much. I can see the blank spot where through the mast 20' in front of me and there's a large spot from the 3" pole.

-- Geoff
BlueJacket
1997 Freedom 40/40
http://www.GeoffSchultz.org

hopalong
Posts: 5
Joined: Fri Jul 10, 2009 1:20 pm

Re: Mast mounting radar

Post by hopalong »

More than 2 years ago we installed our radome on our mizzen mast using a Hysol aircraft adhesive. It is available in 30cc cartridges and very handy. We mocked up the mount with cardboard and a metal outfit dupicated it in aluminum perfectly. We ran the cable down along the mast outside front - inside some dock bumper material. It all has worked well. If anyone is interested we can find our notes and post more details when we return to Mazatlan and the boat early this fall. Sally and David, Hopalong, Freedom 39 Express (we think #1)

Post Reply