AKA Corrosion

I recently received a new AI hull from Hobie Aust under waranty due to a crack in rear scupper. I had to change my old Aka's over to the new hull and found that considerable corrosion (electoysis) had occured particularly to the forward port connection. With the dealer present I drew attention to the enlarged hole in the Aka and requested a waranty claim as the boat is only 20 months old.
The cause of the excessive hole seemed to be caused by 2 factors:

1. The hole appeared to have been drilled out to allow connection to the hull due to original engineering misalignment.

2.The brass securing anchors that were cast into the hull some of which were proud of the deck causing the brass anchor to contact the aluminium Aka with a stainless stud setting up the corrosive process.

The dealer suggested the claim would be rejected by Hobie and user error would be blamed due to poor cleaning, and that is exactly what has so far happened. My enquiry to the cost of new type Aka's from the dealer resulted in a quote of $800. I have asked the dealer to speak again to Hobie with the hope of a fair resolution of the problem.

I suggest owners undo the Aka studs and inspect the connection area to prevent corrosion occuring, and Hobie a separation washer may be of benifit to stop dissimilar metal contact and ability to wash without disconnecting the Aka's. The case continues

Dave, I assume you're talking about the crossbar where it is screwed into the hull, rather than the aka. It seems a bit rich expecting you to rinse out the interface between the crossbar and the hull, assuming it would even be possible to do properly.
HOHUHU posted about the same thing a few months ago: viewtopic.php?f=75&t=39233.
You'd think that any time dissimilar metals have been married in a salt water environment it would be considered a design flaw. Did you submit some photos? I made a claim for aka and crossbar corrosion through the same dealers and they just forwarded the photos to Hobie for consideration, without comment. The claim was accepted pro rata by Hobie.

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Quite right Chris I am talking about the crossbars and yes mine looked the same as NOHUHU's. When the oxidising is cleaned away the connection holes in the crossbars are twice the designed size with signs of distortion and serious pitting.

Yes the dealer took pics and advised me they were sent to Hobie and the response was "claim rejected poor cleaning". I have not given up on the claim.

New steering is better though lee helm is a worry, still some tuning required.

Hmmm, maybe someone from Hobie would be good enough to post some guidelines about what maintenance is expected from owners in this particular area in order to preserve their warranty.
I presume you are expected to remove the crossbars and clean the connectors after each outing.
I haven't noticed any lee helm, but I've mainly been sitting out on the wing since I got the new rudder, so the balance of the boat is totally different.

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[quote="davew"]Yes the dealer took pics and advised me they were sent to Hobie and the response was "claim rejected poor cleaning". I have not given up on the claim.

I would circumvent the dealer and go straight to Hobie on the matter.

Thanks for bring this to everyone's attention. I'll be inspecting mine.

I believe KayakBob commented on this type corrosion 1-2 yrs ago. Maybe he will weigh in with his experience.

This is technically referred to as crevice corrosion, or some variation of it. Wikipedia has a lengthy discussion of the process. http://en.wikipedia.org/wiki/Crevice_corrosion

Here are a couple quotes from the article.
Crevice corrosion refers to corrosion occurring in confined spaces to which the access of the working fluid from the environment is limited. These spaces are generally called crevices. Examples of crevices are gaps and contact areas between parts, under gaskets or seals, inside cracks and seams, spaces filled with deposits and under sludge piles.

and

The corrosion resistance of a stainless steel is dependent on the presence of an ultra-thin protective oxide film (passive film) on its surface, but it is possible under certain conditions for this oxide film to break down, for example in halide solutions or reducing acids. Areas where the oxide film can break down can also sometimes be the result of the way components are designed, for example under gaskets, in sharp re-entrant corners or associated with incomplete weld penetration or overlapping surfaces. These can all form crevices which can promote corrosion. To function as a corrosion site, a crevice has to be of sufficient width to permit entry of the corrodent, but narrow enough to ensure that the corrodent remains stagnant. Accordingly crevice corrosion usually occurs in gaps a few micrometres wide, and is not found in grooves or slots in which circulation of the corrodent is possible. This problem can often be overcome by paying attention to the design of the component, in particular to avoiding formation of crevices or at least keeping them as open as possible.

Long-term owners of AIs know that Hobie has some design aspects that promote corrosion. The attachment of the crossbar to the hull is one.

Keith

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2015 AI 2, 2014 Tandem

"Any intelligent fool can make things bigger and more complex ... It takes a touch of genius and a lot of courage to move in the opposite direction." A. Einstein

"Less is more" Anon

I've had a little trouble with them. HOHUHU problems were more substantial.

I've taken to removing all the hardware from aka and their x-bars every 2-3 years and wire-brush the major problems, sanding the paint peeling areas. I then wipe down with alcohol, and repaint with good quality spray paint.

So far my x-bar corrosion is nothing beyond repairing by added a larger ss washer, but I could see welding being required if the hole corroded so large that the x-bar could move while in use. Most of the bad problems I've seen looked like factory adjustments to make the x-bar fit.

I put a lot of thought into the mixed metal corrosion problem, but I don't see how much can be done. Hobie engineers picked the best materials for the money for each part, and it would be difficult (impossible?) to keep the boat as strong and still keep the different materials from touching (the ss bolts have to screw into the brass fittings, the brass is necessary to attract more plastic during molding, etc.) I thought about a nonmetallic washer between the ss bolts and the x-bar, but there's still ss bolts, rivets and pins in the aka. Unless you can fix all the dissimilar metal contacts, you haven't fixed the problem.

I have a brand new aka set (old style with the ss pin) I purchase as a spare and a extra set of x-bars all painted, ready to swap out in case problems develop when time isn't available, but the whole process can be done in a few hours in one day or so, depending on drying time.

On a lighter note, so far I've used black paint on all my aka parts, but I keep looking at the bright colored metallic (candy apple) spray paints available!

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http://KayakingBob.com - - - - - Hobie Island Sailing since 2006 - - - - - 2011 & 2015 Hobie AIs and a 2012 TI

Can anyone see why the knuckle connection couldn't be welded to the Aka rather than riveted with a dissimilar metal. I can understand why stainless steel rivets are used over aluminium for the strength but without doing the calc's, a stith weld would have the strength, would remove the corrosion issue and although couldn't be replaced by drilling out the rivets, like it is at present, so what ?

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Don't take life too seriously................it ain't permanent.

I don't think then newer style knuckle (not the old pinned one) is made out of medal.

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http://KayakingBob.com - - - - - Hobie Island Sailing since 2006 - - - - - 2011 & 2015 Hobie AIs and a 2012 TI

It's cast aluminum, the akas are extruded aluminum

J

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2011 Golden Papaya TI with a 250 square foot spinnaker!
also a more manageable 100 square foot spinny...
&
the TI3 rear ama mod

Back on the crossbar corrosion issue, does anyone think it might be worthwhile smearing some grease around the receiver holes, then fitting the crossbars and caulking around the interface with some silicone?

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I don't think it would help. You need to keep all dissimilar metals from touching.

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http://KayakingBob.com - - - - - Hobie Island Sailing since 2006 - - - - - 2011 & 2015 Hobie AIs and a 2012 TI

Probably right. Though fiber washers between the metal parts may help. Particularly under the Aka where the saltwater pools over the brass "battery terminal". My Akas revealed that this is where the hidden corrosion progresses, even while the visible stainless bolt and washer areas look clean.



I don't know if gooping up this area would help, but it shouldn't hurt.

It's funny that the wettest areas, with the most dissimilar metal contact (the pinned Aka joints) don't show the corrosion effects. I think it's there, just less concentrated.

On my bars, the sacrificial areas are the underside of the aluminum Aka mount (front/starboard holes were the worse) and the underside of the Aka bars, nearest the stainless pins. Resurfacing and repainting the bars lasts a year or so.



Pop your Akas my friends. If you see aluminum oxide weeping down the hull, it's probably too late already.

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The Wind Is Your Friend... Friends Can Be Fickle

Well as I understand it, you need an electrolyte solution (like seawater) to complete the galvanic circuit. The aka pins are a loose fit, so they are only intermittently bathed in seawater at the same time as the bars. The area under the the aka mount is probably rarely dry, depending how often the boat is used and even when the area dries out, it would leave residual salt, which would draw atmospheric moisture and continue the process.

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We have contacted your dealer and will offer pro-ratta pricing for the cross bars. Please contact your dealer.

Best regards
Steve Fields
Managing Director
Hobie Cat Australia

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Steve Fields
Hobie Cat Australasia
Huskisson NSW Australia
http://www.hobiecat.com.au