Sailing this weekend I noticed a crack in the 3/4" square tubing which connects between the rudder casting and the crossbar.

Link to photos.
http://thebeachcats.com/pictures/?g2_itemId=108042

Any ideas on how to fix it? Square tubing has a compound bend. I can easily buy the 3/4" square tube, but bending it to the correct shape will be challenging.

Thanks in advance for your help.

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Jon -- Dallas, TX
Taipan 4.9
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Depending on the thickness it could be welded with a TIG machine. But aluminum looses about half it's properties (depending on the alloy) when welded. Since it's an extrusion, it should be of the 6XXX series of alloy and something like T6 or T651 heat treatment. With a heat treatment like that, the properties should revert back to about 80% of their maximum after some time. It could be a T4 heat treatment since there's a bend in the tube. T4 is easier to bend without cracking. Over time, T4 properties get close to the T6 ones.

In the first picture, we see a plate riveted to the tube. I would replace that plate with a longer one that would overlap over the crack. I would make it long enough to be able to put a couple of rivet on each side of the crack to reinforce the broken area. It could also be welded. That would be even stronger. If you weld it, don't weld across the tube, Just longitudinally along the side of the plate.



Edited by coolhead on May 06, 2014 - 06:57 PM.

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AB
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I own several TIGs and have welded plenty of aluminum, but I am not an expert so do not take this as gospel.

I wouldn't bother trying to weld that, it cost $80 just to turn my welder on for working on something, I think that's a pretty standard rate. Salt water corrosion equals difficult welding. I think you could make a new arm much cheaper. Mark where you want your bend with a sharpie and heat it until that sharpie mark disappears and then bend it. As for the hardening, I wouldn't worry about it.

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Greenville SC

Offering sails and other go fast parts for A-class catamarans
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Thanks for the ideas. I am going to start by trying to bend a new tube using a benchtop vise. Will try to do without heating first. If that fails I will heat it.

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Jon -- Dallas, TX
Taipan 4.9
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To make a long-term fix (I'm anal about this kind of thing) Take the other side off and take it to a metal bending/fab shop that says they can do aluminum and have them make one just like it, plus a mirrored copy. Then get them anodized (makes all the difference in the world strength and longevity wise) I also like the idea of the longer brace with more rivets. Anytime something breaks on my boat I fix it in such a manner that it will hopefully stay fixed.

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Repairable P18
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