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H17 Crossbar Cracks http://www.hobie.com/forums/viewtopic.php?f=15&t=56858 |
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Author: | Bill 404 [ Sun Feb 07, 2016 12:29 pm ] |
Post subject: | Re: H17 Crossbar Cracks |
I usually drill a small (1/8") hole at the end of the crack before I weld damaged aluminium. Weld towards this small hole and use a heat sink if possible. That should keep the crack from spreading as you weld. Sometimes, I will form a thicker piece of aluminium that wraps around the tubing to act as a heat sink to reduce the chance of deforming the tubing. This extruded anodized aluminium has been stressed in the forming process and can be a real pain to get a good weld. Don't sand or grind down the repair as that will weaken the weld. Leave it proud. Good luck! |
Author: | fastcat [ Thu Feb 11, 2016 12:20 am ] |
Post subject: | Re: H17 Crossbar Cracks |
Your crack looks very familiar. I have cracked 4 front cross beams and one rear one on my 2000 Hobie 17 Sport since buying it in 2002. I replaced the beams with new each time, but that is a bit expensive (though one was under warranty so the replacement was free). I've had my three best front beams and the cracked rear beam welded then reinforce with marine epoxy. Hopefully this will get me through the next few seasons. |
Author: | srm [ Thu Feb 11, 2016 3:48 am ] |
Post subject: | Re: H17 Crossbar Cracks |
I thought about quite a few repair methods and I doubt welding or epoxy are viable long-term solutions. Even if this brings the crossbar back to original strength, we know the original design is only marginally strong enough to hold up and would likely crack again. That's why I'm hoping my band clamp solution works. It is a stronger material (stainless steel) than the original (aluminum), and much better geometry for transferring the torsional "hoop stress" across the tramp track area of the beam. As long as I can get th crossbars fitted to the boat, I think this is going to be a solid, permenant, repair. sm |
Author: | fastcat [ Fri Feb 12, 2016 7:03 pm ] |
Post subject: | Re: H17 Crossbar Cracks |
Time will tell, I break new beams about every 1.5 years. The weld was to bring beam up to original strength, the marine epoxy is the added strength. On your band fix did you have to move the end knuckle up to accommodate the bands extra width? and put an electrical barrier between the dissimilar metals to avoid galvanic corrosion? I have 2 welded backups incase my fix doesn't work out, then hopefully yours does. |
Author: | fastcat [ Sat Jun 11, 2016 10:55 pm ] |
Post subject: | Re: H17 Crossbar Cracks |
Well the epoxy reinforced weld held for about 2.5 months (~200 sailing miles) before re-cracking last week. The bar re-cracked next to the weld and the epoxy failed at the epoxy/aluminum interface. So I changed out to a spare crossbeam and added an end bracket (knuckle) I fabricated to the top ends of the forward beam attaching each with 3 - 1/4 20 SS bolts. https://www.facebook.com/photo.php?fbid=258182977879106&set=a.145239742506764.1073741829.100010622173515&type=3 |
Author: | srm [ Sun Jun 12, 2016 6:06 am ] |
Post subject: | Re: H17 Crossbar Cracks |
What's the thought with this bracket/bolting? Trying to get the end casting to better share the torsional load? I believe the reason the crossbars crack is because the profile of the crossbar is not good at handling the torsional load as the crossbar tries to twist (when one bow tries to go up and the other goes down). The groove for the tramp track basically tries to spread open and the crossbar doesn't have enough material/a generous enough radius around the track section to allow the load to flow around this area. Hence we see crossbars cracking right along the edge of the tramp track. The strap I added goes completely around the extrusion and stops the crossbar from spreading open. If you lock a piece of crossbar in a vice and then mount an end casting to a piece of 2x4, you can easily flex the crossbar open by hand. Adding the strap makes it considerably more rigid. Not sure your solution will achieve the same thing, but I guess time will tell. sm |
Author: | fastcat [ Sun Jun 12, 2016 11:02 am ] |
Post subject: | Re: H17 Crossbar Cracks |
Yes sharing the load is the intent to put both the bottom and top of the crossbar under load. The bolts are bolted into tapped holes in the top of the aluminum end casting. The bolts are in at angles so to decrease stress on the threads. I took the boat out yesterday in 15 mph winds and put her through 25 miles of wave bashing averaging 11.2 mph with lots of hull flying. So far so good. The slight creaking of the beam has gone and it felt real solid. If this solution doesn't hold up to the test of time, I can always add your fix beneath mine, though I'd make the strap a bit wider to accommodate the 3 1/4 inch holes. |
Author: | fastcat [ Fri Dec 23, 2016 6:45 pm ] |
Post subject: | Re: H17 Crossbar Cracks |
UPDATE: Yahoo, the fix worked. After the mid-season front crossbeam replacement and knuckle addition (see above), I sailed the boat about another 500 miles in 5 - 25 mph winds averaging over 8 mph with top speed of over 21 mph (i.e., I drove the boat hard). Took the boat apart for winter and the front crossbeam repair weld held. The beam looks great. I'm thinking of adding the 'nuckles' to the rear bars also. They don't get the stress the front one does, but why not tighten up the boat even more. |
Author: | fastcat3 [ Tue Jan 30, 2018 1:56 am ] |
Post subject: | Re: H17 Crossbar Cracks |
Another update: the front crossbeam survived another sailing season with no cracks. This crossbeam was a welded repair and with the "knuckles" has now survived two seasons now. Previous new and repaired beams lasted 1-2 seasons. So I'm quite pleased. |
Author: | srm [ Tue Jan 30, 2018 5:38 pm ] |
Post subject: | Re: H17 Crossbar Cracks |
Mine’s been holding up as well. Two similar methods for achieving the same thing. Yours couples the top of the crossbar directly to the end fitting so that any torsional load on the crossbar becomes a shear load at the screws you added rather than trying to rotate the crossbar against the end casting, spreading it open. Mine simply adds hoop strength to the end of the crossbar so the crossbar can’t spread open as it twists against the casting. In the end, if it keeps the crossbar from cracking, it’s doing it’s job. I would bet there are a lot of cracked crossbars out there that just haven’t been seen because most people don’t disassemble their boats every year. sm |
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