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PostPosted: Wed Mar 25, 2009 10:42 pm 
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My AI is an 08 model, and a year old. I now have quite a bit of corrosion, on the Mirage Drive at most of the places where the aluminum shafts have a hole, and corrosion crept under the coating, as also on the akas, but some bits of corrosion have started where there are no entry points. I assume its best to sand this off, even if it leaves me with bare aluminum?

I have always washed my boat down with fresh water, particularly the akas and drive, but it seems that's not even enough. Anyone tried to re coat with something more effective? However the entry points where screws or pins are located are always going to be open to corrosion.

Geoff.


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PostPosted: Thu Mar 26, 2009 5:07 am 
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Your almost a temperate climate down there-right? the tropics are an absolute killer as far as corrosion is concerned and i experienced quite a lot after a year where the pedals go into the cranks on the mirage drive and also around the spring loaded pins that adjust the cranks but it amounted to no more than a surface blistering and wasnt deeply pitted like wise my akas...they looked horrible, but again it was a cosmetic issue...at least for me..

Philip


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PostPosted: Thu Mar 26, 2009 6:04 am 
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There is an extensive discussion of corrosion on the AI at
http://www.hobiecat.com/community/viewtopic.php?t=11660&highlight=xbar+corrosion

Here is a quote from me regarding what I think is a fundamental problem w/ the AI regarding corrosion.
Chekika wrote:
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).


I have had no problem w/ my Mirage Drive. I wash it thoroughly w/ fresh water, let it dry for a couple days, and then spray all exposed metal parts w/ "Break Free" aersol spray lubrication. Break Free is recommended by RoadRunner elsewhere on this forum.

Hobie has been quite helpful w/ my aka/xbar corrosion problems. Nevertheless, I have installed 4 saucer-shaped zinc anodes--2 on the front xbar and 1 each on the rear braced akas. It was not possible to place the anodes on the rear xbar because the hull is wider in the rear. However, I do have a pencil anode in the 3/8" hole of the rear xbar. Here are the pictures.
Image
Image
The pencil anode is rather delicate (easily broken off), but it has survived a couple trips.

I'm sure this is "anode overkill," but, given my corrosion problems, I am hoping this fix will work. I will know by next year.

Keith

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PostPosted: Thu Mar 26, 2009 2:57 pm 
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Philip1el wrote:
Your almost a temperate climate down there-right? the tropics are an absolute killer as far as corrosion is concerned and i experienced quite a lot after a year where the pedals go into the cranks on the mirage drive and also around the spring loaded pins that adjust the cranks but it amounted to no more than a surface blistering and wasnt deeply pitted like wise my akas...they looked horrible, but again it was a cosmetic issue...at least for me..

Philip


That is an accurate description of the corrosion, but I wanted someone to confirm that sanding it off would be a good idea. The thread about electrolytic corrosion is nothing to do with what I have. At least at this point. I am getting the surface coating lifting, because salt has got under it.


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PostPosted: Thu Mar 26, 2009 5:25 pm 
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Geoff, I think what you are briefly describing as "surface coating lifting" is corrosion--that is why it is lifting.

Here is a picture of my aka corrosion (it might also be described as paint lifting.)

Image

Sanding it off is fine but you should then put a new primer coat on and paint it.

Keith

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I sail: Biscayne Bay, Everglades to Cape Romano, Ft Desoto, Cedar Key

"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


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PostPosted: Thu Mar 26, 2009 6:34 pm 
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Yes that picture describes the issue, mind you, mine is not really as extensive, yet. What "primer" and "overcoat" is recommended?

Geoff.


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PostPosted: Fri Mar 27, 2009 6:55 am 
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Geoff,

Alodine seems to be the preferred aluminum treatment before being painted: http://www.chemical-supermarket.com/Henkel-Alodine-1201-Chromate-Conversion-Coating-p364.html

I don't have any suggestion for a paint--presumably a good marine paint would do.

Keith

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I sail: Biscayne Bay, Everglades to Cape Romano, Ft Desoto, Cedar Key

"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


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PostPosted: Fri Mar 27, 2009 4:17 pm 
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This does presume that the aluminum needs protection. I guess that was what I wondered. I believe marine grade aluminum is ok? Or is that not the case. My H14 was still fine after 25 years. That's why I thought maybe just get off the bubbles, cause obviously that will be a point of potential trouble, as it traps salt.


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PostPosted: Fri Mar 27, 2009 7:09 pm 
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Geoff,

I don't know about your H14, the Hobie 16 uses black anodized aluminum. The problem the AI has, is that it has steel in contact with aluminum. Steel/aluminum/saltwater equals a "galvanic cell" which I mentioned above. Galvanic cells cause the sacrifical metal (aluminum) to corrode at a greatly accelerated rate.

For still more discussion of the corrosion problem on an AI, check out
http://www.hobiecat.com/community/viewtopic.php?t=11534&postdays=0&postorder=asc&start=15

Keith

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I sail: Biscayne Bay, Everglades to Cape Romano, Ft Desoto, Cedar Key

"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


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PostPosted: Fri Mar 27, 2009 10:42 pm 
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Chekika wrote:
Geoff,

I don't know about your H14, the Hobie 16 uses black anodized aluminum.


They certainly did not all, by a very long margin. Plenty of plain aluminum H16's and H14's. (Maybe there was a clear anodized coating?) And that black anodized coating was way superior to what we have on the AI. It looks like I will try and find a local anodizer, alternatively find some of those products and do it myself.


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PostPosted: Sat Mar 28, 2009 7:08 am 
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Geoff,
Here is a statement about anodizing:
The anodic film is formed by converting the surface of the part into aluminum oxide. Unlike paint, which can flake off if not applied properly, anodized aluminum finishes are actually formed from the original material and cannot flake off. The aluminum oxide finish is very hard and exceptionally wear resistant. Anodizing is good for many consumer products and sporting goods due to its aesthetic and corrosion protection properties. Anodizing is the primary finish for aluminum aircraft parts including major components before assembly and painting.

Anodizing can be done in concert with a dying process which can give the end result a deep rich-looking color finish--like black anodized aluminum, but it can also have a clear finish (the earlier Hobie 16s had a clear finish.)

Again, in my opinion, the corrosion problems with the AI are due to the steel/aluminum/saltwater galvanic cell. A good finish will slow the process, but in the end corrosion will win out--sooner, rather then later.

Keith

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I sail: Biscayne Bay, Everglades to Cape Romano, Ft Desoto, Cedar Key

"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


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PostPosted: Wed Apr 01, 2009 6:55 pm 
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Chekika wrote:
Again, in my opinion, the corrosion problems with the AI are due to the steel/aluminum/saltwater galvanic cell. A good finish will slow the process, but in the end corrosion will win out--sooner, rather then later.


Keith, is it not possible that the corrosion is due to oxidation rather than electrolysis?

Quote:
...aluminum forms a tightly adhering surface film of aluminum oxide when exposed to the air. Under most atmospheric conditions, the oxide protects the aluminum from further corrosion. An exception is found in seashore locations.

When exposed to damp, salty air, most aluminum alloys behave very actively. Sea salt (mostly sodium chloride) destabilizes the normally protective oxide film, leading the localized attack, or "pitting."

http://www2.mtec.or.th/th/research/famd ... metals.htm

Ron P.


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PostPosted: Wed Apr 01, 2009 7:30 pm 
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Ron,

Both actions are oxidation. I emphasize the galvanic cell corrosion because the AI has the elements that are necessary (steel in contact w/ aluminum and both in contact with saltwater). As your link says:
Quote:
Galvanic corrosion is a form of electrochemical corrosion that occurs when two dissimilar metals come together in the presence of an electrolyte
On the AI, the 2 dissimilar metals are steel and aluminum; the electrolyte is saltwater.

Galvanic corrosion accelerates the corrosion of the aluminum as your link says:
Quote:
This exchange protects the more noble (less active) metal [steel], while causing the more active metal [aluminum] to corrode even faster.


Keith

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I sail: Biscayne Bay, Everglades to Cape Romano, Ft Desoto, Cedar Key

"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


Last edited by Chekika on Wed Apr 01, 2009 8:07 pm, edited 1 time in total.

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PostPosted: Wed Apr 01, 2009 7:47 pm 
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The very first akas and x-braces on the Island were anodized. The replacment metal and later '07 and up Islands got the "e-coated" akas & xbraces.

The anodized set were a dull, flat black in color. The newer e-coated ones are a glossy black.

Here is a quote from Matt in answer to why the flat vs. glossy metal. "Glad the parts got there. The difference in color is due to annodize vs "e" coated. We annodized some of the first runs, till we got the e coat process running."

I have 2 Islands; 1 with original flat black annodized akas and another with e-coated akas - replacement metal that is 1 year newer.

Corrosion is very evident on the e-coated while the original annodized metal - even though much older - still looks great.

There was a case of metal wear but otherwise the annodized are vastly superior to the e-coated, side by side it is obvious.
The e-coated ones look sick :cry:

I'm not sure if e-coated is just a sophistocated term for "painting" and I'm not entirely sure why Hobie would abandon annodizing the akas if it keeps them from corroding.

If I had to choose a set it would be the annodized one - provided there were no metal hardness issues.


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PostPosted: Wed Apr 01, 2009 8:16 pm 
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Thanks Yakaholic, that makes sense.

Quote:
Anodizing, or anodising, is an electrolytic passivation process used to increase the thickness of the natural oxide layer on the surface of metal parts. Anodizing increases corrosion resistance and wear resistance, and provides better adhesion for paint primers and glues than bare metal.


http://en.wikipedia.org/wiki/Anodizing

Apparently anodizing is what they do to sailboat masts to keep them from corroding. They are seldom even painted, just bare aluminum.

I guess you can annodize or you can "e-coat" The e-coat works great until the coat gets scraped off or chips, then you get corrosion. But I am sure e-coating is a lot cheaper.

My 09 AI AKAs are glossy black so I suppose they are e-coated. I will look out for corrosion. I suppose I should paint over all areas that where the paint is scraped or chipped off.

Ron p.


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