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Old 17-03-2009, 10:11   #16
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cut off angles and so on

G'Day all,

Following all the above commentary, and finding it interesting indeed. What has not been mentioned yet is that there are big differences in the sharpness of the vertical beam cutoff. I've owned two types of radars -- two Furuno 1700 series and one Anritsu 24 mile (don't remember the nomenclature). The Furunos have rotors which are some sort of phased array (I think) that are simply conductors on a large PCB, and the vertical cutoff is very gradual. On these units, I could not see any significant degredation in performance at heel angles of 25 deg. The Anritsu's rotor was a neat little formed metal elongated dish... with a parabolic cross section I suppose. Looked more like the rotors on "real" radars to my inexperienced eye! I was somewhat dismayed to find that with this unit the cutoff was quite sharp, and that at heel angles of more than about 15 deg targets abeam would disappear from view. Once one knows about this it isn't too difficult to deal with, and I personally wouldn't bother with a self-leveling mount.

So, the advice to experimentally discover how your particular radar performs seems excellent!

Good luck with it

Cheers,
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Old 17-03-2009, 10:16   #17
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Quote:
Originally Posted by meyermm View Post
I purchased the boat with a self levelling mast mounted Radar dome. Radar was at the end of its life so invested in a brand new Furuno unit which failed within six weeks due to cable fatigue at mast exit caused by constant movement. Although the mast exit hole could have been improved my next boat will not have a self leveller.
Ah, Meyermm: installation error! ;-) The cable should be fixed to the stationary part of the bracket after exiting the mast. That way, it will not move at the mast exit hole at all. After that, it should have a generous loop: more than needed for the maximum swing.

cheers,
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Old 17-03-2009, 11:08   #18
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It's going to fail

Quote:
Originally Posted by s/v Jedi View Post
Ah, Meyermm: installation error! ;-) The cable should be fixed to the stationary part of the bracket after exiting the mast. That way, it will not move at the mast exit hole at all. After that, it should have a generous loop: more than needed for the maximum swing.

cheers,
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Radar domes were never designed to swing having the cable flex. That is just an invitation to failure. Even with a generous loop the cable will be flexing and will eventually fail. I don't think to difference of recovered signal warrants this kind of addition.
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Old 17-03-2009, 11:31   #19
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Lancerbye: it's not the radome but the cable itself. The radome is designed to withstand movement, like the boat pounding on waves: swinging about a bit won't hurt it.

So the cable: many apparatus with moving parts have flexing cables. Although I agree that the flexing will shorten their lifespan, this is something more complex than just deciding to not have the part moving. The radar cable will also fail with age, moisture and/or UV, the question is if the flexing shortens the lifespan so much that it becomes a factor. For that, it matters much how the installation is done so that the impact of the flexing is as little as possible. Our radar cable is still fine after 15 years of flexing and who knows how long it'll be okay from now or what will be the cause of it's failure!

I worry more about the starter-cables to my engine than the radar cable with my swing-platform. Vibration is much more a killer for cable because of the work-hardening.

Also, on the other end, it's more than "difference of recovered signal". It's about loss of range which is extreme at the beam if heeled. You basically end up with 2 totally blind spots of 180 degrees in total PLUS reduced range for some of the rest.

cheers,
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Old 17-03-2009, 21:31   #20
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Have you had any luck on the radar mount?
I built my own, but have still not left the dock, so can't comment on how it works, and the cables are just hanging and not sorted.
In the bottom picture you can see an opening between the backstays nylon insert and the pole....this is the path for the SSB antenna connection.
VERY Nice!
I went with a Waltz gambled mast mount.
After a lot of reading there seamed to be two camps as far as gambled usefulness goes. I went with my own sense of logic and got one. The other fairly consistent opinion was that height of the mount added the most benefit, so I went mast mount. Also, I will have my Cape Horn Wind vane, solar panels and a wind generator on the stern, so I thought it was going to get too busy back there. I also had concerns over the weight and possible harmonic vibration on my wishbone back stay.

You certainly did a nice job.
Hope it works well for you.

Thanks for asking.

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Old 18-03-2009, 03:51   #21
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Thanks Extemp....I hope it works too!
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Old 18-03-2009, 05:12   #22
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The benefits of better signal only improve for target on or close to the beam. Targets on or close to the bow or stern headings are not improved at all by self leveling mounts. So the improvement is effectively only at the beam ie 10-20% of targets encountered.

The fatigue is bad enough but this is increased by exposing the cable to more UV which degrades and stiffens the cover which will hasten the cable fatigue. Fixing the cable at the "exit" only localizes the fatigue at the exit though it will decrease the possiblility for chafe to zero.

Self leveling is a bad idea, expensive with little benefits and plenty of downside risk. And replacing a radar cable ain't fun either.
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Old 18-03-2009, 10:32   #23
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defjef: read the thread and you will find that the "problem-angle" is 90 degrees off each beam. That is a total of 180 degrees when heeled.

Number of ships encountered: only 10-20% affected? So, most ships sail in the other 180 degrees? This will only be true if you're following a shipping lane. If you cross one, it's the exact opposite and anywhere else it'll be random. I could not live with targets disappearing when they move to the beam or loosing the shoreline I'm following etc. That is not the idea of radar. Also: ships crossing my bow or stern are nice to see but ships coming for my beam are the ones that bring danger. Don't forget that these guys come with 16-20 kts speed!

chafe, fatigue and UV: all true but irrelevant when the cable still outlives the rest of the installation. Also: for each of these are counter-measures just like for corrosion of contacts etc. (chafe: immobilize cable where it touches something; fatigue: minimize flex by creating big loop; UV: sleeve the cable)

cheers,
Nick.
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Old 18-03-2009, 10:57   #24
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Quote:
Originally Posted by s/v Jedi View Post
defjef: : for each of these are counter-measures just like for corrosion of contacts etc. (chafe: immobilize cable where it touches something; fatigue: minimize flex by creating big loop; UV: sleeve the cable)

cheers,
Nick.
Thats the plan
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Old 04-02-2011, 14:41   #25
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Thats the plan
This is an old thread, but I'm curious James, how did you end up moutning you RADAR to mitigate the concerned of chafe and UV damage?

Especially what you did you use if anything to provide additional UV protection to the cable as it exits the mast and loops to the radome.

Thanks,
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Old 04-02-2011, 19:42   #26
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I was very happy with my scanstrut backstay mount sailing around Chesapeake Bay and up and down the coast. I was very unhappy when it failed 400 miles into a 1300 mile passage and I had to tie down the radome to avoid the whole thing ripping itself out of the transom. At this moment I am in St. Lucia waiting for a mast mount bracket that will work with my radome - I wouldnt do an ocean passage with such a setup ever again. Casual observation around Rodney Bay showed only one self levelling backstay mount - mine - and it is about to be removed along with the duct tape, pieces of stainless steel, and random hose clamps that are currently holding it together.
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Old 04-02-2011, 22:14   #27
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I haven't had any problems as of yet.
The chafe guard I ended up installing is that black plastic spiral split stuff used to organize/combine computer cables.
I haven't been in any heavy weather with her since the install...so I don't know how robust it will turn out being....but the fair weather sailing/passages hasn't broken anything.
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Old 04-02-2011, 23:08   #28
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We've had our Questus self-leveling back-stay unit work very good since it was installed over four years ago, and I'm sure it will work fine as long as we own the boat. There is no sail chafe mounting the radome to the rear of the boat, and the cable is fairly well protected by UV by exiting the bottom of the radome and going right into the pole...a matter of maybe 12". This Questus unit was ordered with a heavy duty pole (larger diameter than normal), with the bottom of the pole secured in conjunction with the back-stay at a stern chainplate...very solid. There is very little movement of the Garmin radome cable, and the cable covering is nice and thick. I prefer the radome to be lower than on the mast, because I'm more interested in seeing closer in targets.
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Old 25-03-2011, 10:03   #29
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Re: Self-Levelling Radar Mount

My last boat, a Tayana 42 CC, had a mast mounted self leveling radar mount. I used it for 5 years without the failed wire issue. The secret to keeping the wire safe is having a good sized service loop in the wire at the point where it swings. This keeps the flexing to a minimum as far as the wire strands are concerned. The hydraulic dampening also helps. Some extra wire was left under the headliner to be pulled up if the loop wires ever did fail.
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Old 26-03-2011, 20:40   #30
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Re: Self-Levelling Radar Mount

Have had one for 8 years, no problems except a nut hit me on top of the head once, telling me it was time for some fastener maintenance. Complacency will get you every time!
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