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PostPosted: Mon Jan 26, 2009 6:31 pm 
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Looking at the center underside of both AI xbars (both new and old boats), there is a 3/8" hole. It seems to me that this is regularly going to take on salt water, and, unless it is washed out after each salt water outing, it is going to cause serious corrosion problems.

Why is that hole there? Perhaps more importantly, why is it not sealed w/ marine goop?

Kieth

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PostPosted: Mon Jan 26, 2009 9:05 pm 
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Only guessing but Its probably a drain hole there are 2 jam cleats on the xbar that are bolted thru if water can get in there and has no way out then you would really be in trouble!


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PostPosted: Tue Jan 27, 2009 4:55 am 
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My guess would be that it is a datum point hole for manufacturing. Kinda like a pivot point for when they are flattening the ends, to end up with a symmetrical piece to give to the welders...

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PostPosted: Tue Jan 27, 2009 6:18 am 
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Philip--both xbars have the hole so it is not because of the jam cleats.

Yes, I suspect it is part of the manufacturing process, but it is unsealed in any way, i.e., on a new xbar it has shiny aluminum showing. I think, when the inside of the xbar is clean and dry, this hole ought to be sealed with marine goop.

Keith

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PostPosted: Tue Jan 27, 2009 9:00 am 
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Chekika wrote:
Philip--both xbars have the hole so it is not because of the jam cleats.


I think they're identical, so during manufacturing they are not yet designated as forward or aft. Don't know which ones might get jam cleats and water inside, so put drains on all of them.


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PostPosted: Tue Jan 27, 2009 11:03 am 
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Very good rationalization, Tom, but I do not think the large 3/8" holes are to drain the xbar. The screws for the jam cleats are quite tight. I doubt they leak. Secondly, the left front aka which has the paddle cozy on the 09 AI has holes for stainless steel screws, but there is no drain hole in that aka. Since corrosion can be a problem, especially for saltwater sailors, I still wonder why these holes are not sealed to prevent serious saltwater intrusion and retention?

Keith

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PostPosted: Tue Jan 27, 2009 4:36 pm 
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Likely what you are seeing is a hole for drainage during the production process. The parts are dipped in chemical / fluids at some point.

Why not sealed after? Not sure, but we have the same (open) issue with many booms, crossbars and other parts for the cats with little if any ill effect over time.

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PostPosted: Tue Jan 27, 2009 4:48 pm 
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For a new AI xbar, this hole is as bright and shiny as a newly minted nickel--very bright, very clean bore. It is so clean it looks like it was put in after the bars were painted. In any case, given my problems w/ corrosion, I am going to seal these holes (one in each xbar) and add a zinc anode to each bar.

Keith

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PostPosted: Tue Jan 27, 2009 4:50 pm 
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If you seal this hold off I would be worried about an un know leak around a fitting and a small amount of water would be trapped inside and cause unseen corrosion. As Matt pointed out several booms have a similar hole and have caused no problems.

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PostPosted: Tue Jan 27, 2009 5:56 pm 
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One item that still seems lost on people here is galvanic corrosion. I have mentioned it on a couple theads on this forum, but it needs to be said again. If everything is made out of a single metal, say aluminum, it is not a problem. But, if you have 2 metals like steel and aluminum in contact, and these metals are in contact with salt water, then you have what is known as a galvanic cell. With a galvanic cell, the sacraficial metal (aluminum in the case of steel/aluminum cell) corrodes very rapidly. I don't know the situation with a boom, but I do know that the AI has numerous steel/aluminum connections. This is asking for trouble in a saltwater environment.

Hobie has been very generous with me and my corrosion problem--they deserve their reputation for outstanding support. And, I am very thankful for Hobie's hosting this forum for users to exchange information. The information on this forum is invaluble. I and others have expressed this opinion frequently. So, I am bringing up this potential corrosion problem with constructive intentions.

My use is special. I only do multi-day kayak camping trips. Most of the trips have been outlined on my thread about "expedition" kayaking: http://www.hobiecat.com/community/viewtopic.php?t=7276&postdays=0&postorder=asc&start=15 Of course, on these multi-day trips I cannot wash my equipment at the end of each day. Further, I only sail in saltwater, so corrosion problems are going to be amplified 10-20 times compared to fresh water.

Now back to the "hole." This unpainted aluminum surface which, through conduction, is in contact with steel (the steel hinge pin and screws) will cause undue corrosion when used in saltwater. I am going to try to prevent that corrosion by (1) attaching zinc anodes to the xbars, and (2) sealing the 3/8" hole with marine silicone sealer. I also intend to seal the 4 holes of the jam cleats and the 2 holes of the paddle cozy with the silicone sealer.

Hopefully, a year from now I will be relatively corrosion free. We will see.

Keith

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PostPosted: Wed Jan 28, 2009 2:02 pm 
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Note that corrosion from dis-similar metals is usually limited to the contact points of these materials.

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PostPosted: Wed Jan 28, 2009 2:24 pm 
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Sorry, Matt, that is not true. Galvanic corrosion is an electrolytic process, i.e., it occurs via transmission of electrons through the metal. The corrosion will occur anywhere on the aluminum surface where it makes contact w/ the saltwater. Here is a quote from Michael Kasten's web site: Aluminum is very active galvanically and will sacrifice itself to any other metal it contacts either directly or indirectly. Aluminum is anodic to everything except zinc and magnesium, and must be electrically isolated from other metals. (Kasten Marine Design, Inc.) As Kasten says, aluminum...will sacrifice itself to any other metal it contacts...even indirectly--that is, they do not have to touch. All they need for the aluminum to corrode (sacrifice) is to have a metal or wire connecting the aluminum to the other metal (steel, for example.)

The consequence of this for the Hobie AI is that a steel pin in the hinge will cause the aluminum bars to corrode anywhere the sea water touches the aluminum. Painting the aluminum is an attempt to reduce contact with saltwater, but any scratch or nick in the paint will start the galvanic corrosion process.

Zinc and magnesium are the only metals which sacrifice themselves in contact with aluminum. That is why I have added a zinc anode to each xbar. Zinc anodes can be purchased at most general marine stores (West Marine in the USA).

Keith

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PostPosted: Wed Jan 28, 2009 2:38 pm 
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Salt corrosion does not require dis-similar metals issues I would think, so scratches in paint or annodize will show corrosion anyway.

The biggest issue with the corrosion to your bars was the defective electro plate process.

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PostPosted: Wed Jan 28, 2009 3:12 pm 
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As is pointed out many times on the web as well as in scientific texts, galvanic corrosion is much more serious than simple single metal corrosion. We don't have to worry about why, but it is necessary to understand that an aluminum/steel galvanic cell is death to the aluminum. Until Hobie reduces the steel to aluminum contact on the Hobie, there will be serious aluminum corrosion. Adding zinc anodes to the bars may also eliminate or reduce the problem.

I just returned my bars to Hobie yesterday by FedX. I don't think Hobie has had a chance to examine them to determine the problem.

Keith

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PostPosted: Wed Jan 28, 2009 10:57 pm 
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I'm no expert in such matters, but like your idea of using zinc as a sacrificial anode if you're having galvanic corrosion issues. Nevertheless, I would keep the hole open as a vent/drain as Hobie designed it, add your zinc for galvanic protection where it can be accessed it for periodic inspection and replacement and enjoy the new piece.

If you decide to seal the hole anyway, you may wish to blow in it first and verify that it is no other air leak and consider whether condensation or humidity may create a moisture problem. BTW, how does your stainless/aluminum Mirage Drive look? 8)


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