broken gps mount

S

starcrafttom

Active member
I am having a problem with the GPS mount breaking every 300 hours. I have a metal mount that bolts on my radar arch. It has a round base that clamps around the tube of the radar arch and has a round upper part that can be locked in place, up or down, with a lever type lock. I am not describing it very well but many of you have one for your GPS or your vhf. In the last two years I have had two break while under way. Once while on the trailer and once while boating. It seems to me that the thin piece between the upper locking part and the lower mount is getting futigued and breaking. I beleive that the space ship design of the Gps head is causing the whole thing to wiggle back and forth while trailering. These units, if you can find one, are $50.00 each. this is a item that should not be breaking. Has any one else had this problem? Does anyone know where I can order a replacement cheaper the $50.

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Is your unit Stainless steel, brass or pot metal? The Stainless steel should be much stronger than the others. I have used similar mounts for VHF and GPS, but flat mounts on the cabin tops for many years and never had a failure...
 
Not brass or pot metal. I beleive its stainless. Thats why its $50 a pop. I know the photos are mot good. I will try tomorrow for some better ones.
 
That looks similar to the SHAKESPEARE 4188 SS RAIL MOUNT. I found them for $25 plus s & H. I wonder if there is a defect in the brand or a batch you have been using. The basic mount looks similar to what is in common use, just the railing mount is different than the flat plate mount.
(Current boat running 8 foot Digital antennas at up to 40 knots and into 3 foot seas, with no problems so far on the flat mount (backed by fender washers on the cabin roof). Maybe you might consider putting the GPS on a flat mount--or changing brands? I am still not sure where the break is occuring.

Regards,
 
starcrafttom":3molal2z said:
heres the pic from the web site.

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Click to expand...

Tom- From your photos and descriptions, the mount is breaking at the thin point between the lower rail clamp-on part and the upper adjustable angle setting part.

I don't know how thin the mount is at this juncture, but metal fatigue must be a factor.

I wouldn't think it would break if it's stainless, but I don't know how narrow it is at that point.

Here's a thought: Most antennas are long whips that sway with the wind and boat motion. There's a lot of stress on them, but it's applied gradually with the whip motion.

Your GPS antenna may be a medium length shaft with a round weighted antenna on the end, in effect an upside down pendulum. The motion of this may be more abrupt than a whip antenna. This motion may fatigue the metal more than the more gentle whip motion.

I'd get a magnet or compass and try to see if the material is magnetic and also how hard it is with a file, just for curiosity to see if it's stainless.

You might talk over the phone or by e-mail to the company's technical rep about this problem to see if it's common, or what they think.

The easiest solution may be to just substitute a very robust fitting without that narrow section, even if it means going from a rail mount to a flat flange with fender washers or a plate below on the other side of the fiberglass.

Hope this makes sense and is helpful!

Joe.
 
Joe you nailed the problem and yes it is stainless. I think that the big wide head on the gps is shaking the mount while towing at 60 mph. I have looked into other mounts that dont have the thin neck but they do not allow for the ant. to lay flat with out rubbing the rail. I was just wandering if anyone else has this problem or is it just a bad luck.
 
A couple of further comments--the only reason to get a GPS off the cabin top is either lots of obstruction from metalic objects (and a Bimini is not enough). I see lots of GPS antennas mounted up 3 to 4 feet on a mount like this. Mounting this high is totally unnecessary. Both of my current GPS antennas are cabin top mount--and about 3" off the cabin top. There are VHF antennas, Ham antennas, Radar etc above them--and the GPS works perfectly. There are enough satellites, so that if one is obscured, the others will fill in with no loss of accuracy.

Second--in towing, bring all antennas down to deck level--don't leave them whipping up in the wind. If the GPS antenna is on a 2 foot lever arm, it multiplies the force by many fold--and will cause failure.

Just be sure that the GPS is out of the plane of the Radar beam--about 30 degrees total (15 above and 15 degrees below horizontal).
 
Tom,

Have you thought about mounting it without the extension, and directly on the radar arch? I assume your arch has that area for one that sticks out in the back like mine does. Or does it need to be above your radar? I would also contact either the manufacturer or place you purchased it to let them know your burning through them. They might give you a replacement.

Sark
 
Looking at your albums, there would be a number of options of monting the GPS much lower--and still out of the 15 degree down cone of the vertical Radar beam. There are several reasons not to put a GPS up high--one is the stress you are experiencing, another is the arc which it is going thru as the boat is rolling is accentuated the higher up. I get good receptions of GPS satellites from a unit on the dashboard of the RV, windshield of all of the cars, and even the East facing window of my bedroom.
 
I am not sure mounting the GPS antenna on top of the cabin is even necessary. My GPS has a small antenna that I place on my top shelf inside my cabin. I have never had a signal problem with it.
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Dave dlt.gif
 
I don't know the manufacturer, but with some knowledge of casting metals, that design is likely to have porosity, or early cooling at that constricted area, making the final casting weak and susceptible to flex fracture.

Maybe a call to them would get you a replacement or better design. Lots of good ideas here already.

John
 
Tom,

Mine is mounted the same way but I always lower it to horizontal before trailering and have never had a problem (yet).

Mine is mounted on a 2 ft extension and I was thinking about it as I was doing 60 mph into a 40 Kt. headwind today (in my truck not the boat !!) that would mean that if it were extended I would have more than 100 mph wind on that hockey puck antenna with a 2 ft leverage at the base !!!

I can also imagine that at some speed you would hit the mechanical resonance of the system which would fatigue it in very short order.

That's my 0.2c worth. Suppose I'll start breaking them too now.

Merv
 
gurmpy, i do fold down the 2 ft extention when on the highway and i think thats the problem. the gps head is so wide that it shakes in the wind. I just did not know if it was just my unit having problems. so far I guess it is.

everyone else,, I was wandering if the unit would work from inside the boat on the shelf. I did not install the unit on top but just assumed that it was a good spot. les has installed many units in this way and I have not heard of anyone having one break. I do like the way it looks but may shorted the lenght or moving the unit.

I have seen somewhere a gps head that was shaped more like a hotdog then a UFO. That would keep the wind from shaking the base so much. I have not decided how I will fix the problem. If I move the the head to the shelf I will beable to run a second ant., am/fm for the radio. I get louse reception on am. I have the a combo vhf am/fm ant. ran thru a splitter now.
 
Hi Tom,
My GPS antenna and mount appears to be exactly like yours....also mounted by Les. Mine has not been a problem. Tomorrow, when I get home from work, I'll take a close look at the mount and see if there is a problem, I'm unaware of. (I fold mine down towards the stern when trailering.)
 
My mounting is also the same as above on a 2' Shakespeare extension & Raymarine GPS. No problems in over 5,000 miles towing and 2,500 Kn miles on water, but like DaveS, I'm going to look over the mounting for possible fractures. Thanks for bringing this to our attention.
 
Tom,
Thanks for clarifying that you tow with it down.
You are right, twice is a bit much. Mine was also installed by Les so is probably identical.

One more thread of thought along the same lines:- Do you have the tall or short radar tower ?? Just thinking it might be caused by turbulence off the rooftop. Mine is a tall tower with standard roof.
Having spend my career messing with airplanes and vibration issues I have seen some funny things.
Not that it helps much because in the end you either have to move it or find one that doesn't break.

happy turkeyday

Merv
 
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