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PostPosted: Wed Apr 17, 2013 11:59 am 
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Joined: Sun Sep 06, 2009 2:04 am
Posts: 9
Thanks both for your replies. I suspect from my own experiences that importing a single hull from the US to Brazil would be such a logistics, customs and import tax hassle, up to the point that one has to consider the boat to be a total loss. Considering this, I really can't blame Hobie for not wanting me to send a new hull. Doesn't really help me, though.

Am I right in suspecting that Hobie replaces these hulls so readily with extended warranty conditions because they are probably irreparable? Matt, somewhere else in the Forums you mention that warranty DOESN'T normally mean a new hull, but a Hobie sponsored repair by a dealer. Thus I imagine that this type of repair must be rather hopeless, since you offer the hull replacement. Ripit's story seems to suggest as much. Still doesn't help me, then.

Thus remains me to muddle on, waiting for the new Brazilian distributor to come online. Thanks very much for pointing this out to me, Matt. Even so he would probably be located 100's of miles from where I am, Brazil is so enormous and logistics gargantuous...

Considering all other options difficult to implement, still no repair advice? I would need an adhesive that will chemically react with the polyethylene surface, creating an interface stronger than the original polyethylene matrix... I was thinking of a 2-component epoxy adhesive, applied from both sides. Would it not even hold for a while, breaking at first use of the mirage drive...? I would consider it worth it if it would hold say ten days of sailing. It is easy enough to re-apply. Or would there eventually be structural damages...?


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PostPosted: Fri Apr 19, 2013 10:18 am 
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...hmmm, being a chemist, I tried to come up with a chemically sensible strategy to the problem. I learned that polyethylenes are basically polymeric alkanes which only have C-H groups on the side, set in a thermoplastic matrix. Just about the most chemically inert a polymer can get, and very hydrophobic to boot! No adhesive is going to react with this matrix to form a stable interface. My first experiment with the 2-component epoxy showed as much: a very strong epoxy layer was formed which penetrated about 3 mm into the crack, but it readily peeled off, without leaving any debris! This is going to be tougher than I thought. Thus, what we need is a thin, runny adhesive that readily penetrates the crack through capillary suction, then polymerizes on both sides of the crack to form a solid block, thus unable to leave it. I have here a runny, non viscous cyanoacrylate adhesive (aka "super glue") which will be experiment no. 2. Polymerization is induced by water, so it should feel fine in a humid environment! Let's see... If that doesn't work, I start to believe we have to melt down the polyethylene matrix to create a new thermoplastic grid...


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PostPosted: Fri Apr 19, 2013 2:22 pm 
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Joined: Sat Feb 18, 2012 11:47 am
Posts: 75
Location: Texas Gulf Coast/Dallas, Texas
Hey Matt, I love the New Hull and the Rudder. Thanks for the Help!!!

_________________
"Riding The Island Wind" RIPIT (Tim)
'08 Red Hibiscus AI w/2013 replacement hull, Lovin' it!!!
'11 Golden Papaya AI (for a chap)
'10 Outback w/sail
'11 Tarpon 160


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PostPosted: Fri Apr 19, 2013 2:29 pm 
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Joined: Tue Jul 19, 2005 6:29 pm
Posts: 1893
Location: High Point, NC
My brand new AI had a crack in exactly the same place. Although Hobie offered a replacement hull, I thought I would attempt to spare both of us some time and expense by plastic welding the crack.

It not only worked, but to date my AI has not taken on a single drop of water inside the hull in roughly 2 dozen trips, some of which have been for hours at a time in some pretty choppy water.

Most likely it can be repaired successfully. The only question is do your or your dealer feel confident in tackling the job? Worst case scenario is that the repair wouldn't be successful in which case I would think Hobie would still replace the hull provided the terms are worked out beforehand.

In my opinion, any sort of structural crack or break in these plastic hulls is always best repaired by plastic welding, not the use of an adhesive Properly done, the result is a good as new hull with no weakness nor tendency to failure in the repaired area.


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PostPosted: Tue Apr 23, 2013 12:26 pm 
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Thanks a lot Tom, love to hear that someone successfully repaired this one. I get the impression that you are right and welding the thermoplastic matrix is the way to go. Nevertheless I don't posses the kit and might have a problem laying my hands on it in this place. I also understand it does take some experience. I just applied the cyanoacrylate adhesive and this one seems to have a stronger bonding to the polyethylene matrix. It passed the bubble test, I just need to test it on the water. I guess that I didn't lose a thing if it didn't work out (my previous attempt with the 2-component epoxy peeled off readily without leaving any debris). If I don't pass the praxis test, I will put effort in the thermoplastic welding option, thanks to your advice.


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PostPosted: Tue Oct 29, 2013 6:57 am 
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...so we are a few months further. I moved and don´t live near the sea anymore, so in future in-land lake trips, the boat is likely to suffer less wave tension.

To test leaking in the boat I use the method descibed elsewhere in the fora:

viewtopic.php?f=71&t=46579&hilit=leak+test+air+pump&start=0

Now the interesting observation: when you pressurize the hull like that, the crack opens up a millimeter or so! I imagine this basically mimics pressure fluctuations when the boats gets hit by waves or any mechanical pressure on the hull. It´s like large weak pressure on the hull gets levered into very strong, localized forces near the crack. this might be what caused the crack in the first place, and also makes it very difficult to repair. My last glueing attempt with cyanoacrylate (=super) glue looked very solid, but as soon as I go on the water the crack returned and I started collecting water again.

So this time, after further internet study I decided to plastic weld the crack, even though here in Brazil I cannot get the proper gear. I learned that basically any polyethylene resin (e.g. from certain plastic bottles) will do as a welding material. Then all you need is a way to heat polyethylene above its metling point (120 0C) but below it burning temperature. For that purpose I will modify my normal (metal) welding rod with some wire on the tip, so it will become hot but not as hot as its normal working temperature.

Then I will try to weld the crack while my little air pump is blowing air in the hull, so the crack is in the "open" position while welding. This way i hope to reduce the effect of the crack being opened later on the water by external pressure.

Anybody feels like giving me a heads up before i will go ahead? Again, sending the hull back and forth across the globe doesn´t seem to be an option...


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