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Old 07-07-2010, 14:39   #1
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Radar Arch / Tower - Construction Material . . .

Hi...are there any metal experts out there?

I'm getting quotes for our radar/solar panel arch and I'm getting different feed back from different welders and metal workers.

One fabricator says he won't fabricate anything in aluminum due to the poor tensile strength properties. He states he has repaired too many aluminum arches to count and only does fabrication of arches in stainless steel.

Another fabricator I talked to said he could and would do it in aluminum if I wanted. It's about half the cost compared to s/s. He said he has done many jobs using 60/63 grade aluminum. He said it has very high grades in anti-corrosion and welding.

Does anyone have any feedback regarding either of them?

What is your experience with aluminum vs stainless steel for arches?
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Old 07-07-2010, 14:54   #2
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I have an A-frame (an inverted U-shape actually) made of aluminum. Its somewhat similar to an arch but can support one hell of a lot more weight. I had the two corners bent in a very large industrial pipe bender which makes it very strong for its weight.

If the engineering is done properly using the proper type and sized materials etc, aluminum is not going to permanently deform or crack. The nice thing about aluminum is that it has a better strength to weight ratio than stainless and if you don't mind the dull gray finish that it eventually gets, you don't need to paint aluminum. On the other hand, stainless is of course the prettier of the two metals.
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Old 07-07-2010, 15:55   #3
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I had one made 3 months ago. I chose aluminum hands down. To my knowledge aluminum is lighter, cheaper, and stronger (for the weight). It also happens to work aesthetically for my boat, which I think is the only reason why a person might choose stainless.

I think most catamaran (i.e. big) arches are aluminum. My span is 15 feet and the legs are 2" schedule 40 pipe. It supports 200 lb dinghy, 150 lb motor, 150 lbs of solar panels, plus 200 lb of me with no trouble. It weighs less than 200 lbs and two men can carry it easily.

I think you will find that good welders only do one or the other metal. They take different tools and different skills. I noticed that most of the business for these guys is making t-tops and towers for fishing boats.
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Old 07-07-2010, 16:04   #4
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Interesting, I am thinking of the same thing, an arch for wind generator and solar panels and maybe to hold the Porta Bote.

I see you used 2" schedule 40 pipe. Was this aluminum electrical conduit by any chance? I have looked at that and think it might be the most reasonable material.
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Old 07-07-2010, 16:11   #5
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Here's a picture of mine. It's made from aluminum and I'm happy with it. It doesn't have to lift my tender but could. If it was used for that, I'd add some cross stability as that seems to be the only point where it shakes (side to side very slightly).
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Old 07-07-2010, 16:14   #6
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I see you used 2" schedule 40 pipe. Was this aluminum electrical conduit by any chance? I have looked at that and think it might be the most reasonable material.
No, mine was made with bright anodized stuff intended for fabrication. I believe the schedule 40 is just a standard for size and thickness. If we had needed more strength we could have gone to schedule 80. If I were going to paint it we could have saved money on the metal and used mill finish stuff, which I assume would be similar to conduit.
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Old 07-07-2010, 16:26   #7
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Don't go to Home Depot electrical for your aluminum. You need a grade of aluminum that will hold up in a salt water environment. Not every grade is suitable in a marine environment. Call someone who does aluminum welding for boats professionally, they will know. There are a few different grades.
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Old 07-07-2010, 17:18   #8
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Mine was built of anodised Al by a professional who has built many. It supports solar panels and supplies shade and replaces the stern pulpit to keep me in the boat. My boat is capable of speeds of 20 to 22 knts and that produces a rough ride and the arch has held up fine and provides welcome security in the cockpit. Dave
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Old 07-07-2010, 18:02   #9
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You may consider a large diameter aluminum tube (3.5in in the photo). I plan on building a similar design with 4.5in tube. Larger tubes eliminate much of the webbing and welding costs, while adding strength.
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Old 07-07-2010, 19:41   #10
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You may consider a large diameter aluminum tube (3.5in in the photo). I plan on building a similar design with 4.5in tube. Larger tubes eliminate much of the webbing and welding costs, while adding strength.
Looks real nice. I assume you welded on prefab 90 degree elbows? 2.5" is the thickest I've heard of having custom bends.
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Old 07-07-2010, 19:45   #11
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Yes, those are welded 90 deg pieces.
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Old 08-07-2010, 06:23   #12
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CAELESTIS,

Those 90 deg bends, did you open them up a little? They look a little more open than 90 from the photo.

And are they butt welded or did you weld them over a sleeve?

I think it looks great, probably would not work for what I want but I love seeing the various approaches out there.
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Old 08-07-2010, 08:46   #13
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Thanks for the feedback....I think this is a great thread. I was looking for a userfriendly program to start sketching up my arch in 3D and I found the Google application called Sketch-up for either the MAC or the PC. So far it has been working great. Thats a hell of an arch above, on Caelestis!
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Old 08-07-2010, 08:50   #14
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That arch is not on my boat, but I plan to use it as a model for one I plan on having built soon. I think it is the best looking arch I have ever seen.
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Old 08-07-2010, 09:39   #15
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Personally I would stay with Stainless. A friend has one made of aluminum and it is corroding where the steel bolts come in contact with the aluminum.

If you do go with aluminum try to use large diameter 5083 alloy tubes.

Aluminium and Aluminium Alloys - Designations
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