Crack Under the Front Crossbar

My Hobie 16 is about 12 years old and I've noticed a crack under the centre of the front crossbar where the rod goes through.

I've removed the mast-step and rod that goes down to the striker with a view to having a plate welded next week.

Any advice appreciated please.

Photos: http://www.johnahern.net/page89.html

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The crossbars are made from 6061-T6 aluminum. This is a heat treated aluminum and the heat treating process adds considerable strength to the aluminum alloy. By welding the crossbar, you willl anneal the aluminum which is to say you will undo the heat treatment. This will make the crossbar significanly weaker in the heat affected zone of the welds.

If the crack is very small, you may be able to drill a small hole at the end of it which will stop the crack from growing. I did this to a Hobie 17 crossbar and it worked OK. Otherwise, you would be better off replacing the crossbar. Welding is generally not recommended.

sm

Here are some photos.......
http://www.johnahern.net/page89.html

My guess - that crack developed because your dolphin striker was loose.

Follow srm's advice and drill a small hole at the end of the cracks to stop the propagation.

To reinforce it, get a piece of an old crossbar and cut out a 6" long "patch" from the same part of the section, so it will already have the proper compound curve. Use 3/16" stainless or Monel pop rivets to attach it. 1" spacing on the rivets should do the trick (~14 rivets to attach it).

Round the corners on the patch and relieve the edges (smooth out the sharp corners on the outer surface) so it won't snag or cut anything.

Make sure the dolphin striker rod is tight. It should have a "thummmmm" sound when you hit it with your hand. If it clanks, then it's loose.

Between the crack and the oversized rivet holes, I wouldn't even mess around- just replace the crossbar. They can be found used on ebay and craigslist all the time for cheap. The crossbars are not components worth risking failure. Yours is cracked on both sides of the striker post hole several inches. I would never have full confidence in it, even if repaired.

sm

Overall, a good plan for making a repair but I just have to ask what is the deal with using ss or monel pops for a repair of aluminum parts? Yes, they are probably stronger (in shear) than aluminum... but you are just setting up a 'battery'* for corrosive processes. Not considering the additional cost and strain to install them. I would use an adequate amount of aluminum rivets- on aluminum- and not worry.

*http://corrosion-doctors.org/Seawater/monel.htm See 'Galvanic Corrosion...
http://www.airforums.com/forums/f4/is-stainless-steel-corrosive-to-aluminum-49955.html

That said, the whole repair will still be suspect in any case and I'd look for a deal to eventually replace it.

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Raise your sail one foot, and you get ten feet of wind.
起你的一只帆，和你10英尺的。 -- Chinese Proverb
William D. Latinette @ Latrobe, PA, USA w. H14 Turbo X 2... [email protected]

They are not "probably" stronger - they are stronger - about 2 1/2 times stronger, to be precise.

Consider that that Pop rivets are mostly hollow. Remove the shank, and I can cut an aluminum Pop rivet with a pair of scissors. Try that with a SS or Monel rivet and you'll end up with broken scissors.

The effects of galvanic action are insignificant in the short term and negligible in fresh water. Why do you think the entire boat is put together with SS rivets?

Do I really need as many as 14 rivets?

Finding a s/hand crossbar is hardly an option in South Australia and anyway the frame has been glued. I have a crossbar from a wreck that's good for a patch. That one is cracked in the same place - as was my previous boat - seems to be a common problem.

Thanks to all for the advice. J

Repaired with 16 1/8 rivets on a patch from an old crossbar. We used West Epoxy and filler underneath. The patch came form a H16 wrecked by the local Tsunami Brothers--one of many cats they've wrecked!
One day I rescued their 'crew' (the wife) after she'd been hit on the head by the improvised boom--a piece of 2x4--and knocked overboard.
The second time I plucked her outta the sea after she'd dislocated her shoulder.
I believe she now lives in the outback!


Photos:
http://www.johnahern.net/page89.html

Thanks again for all the advice - lucky I had Stuart's help!

_________________
Catamaran-Dogamaran on YouTube - starring Chloe the neigbour's dog
http://www.youtube.com/watch?v=d1G9FpnTIOI