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Discussion Starter · #1 ·
Hi all,

I have a 1988 Grady White Overnighter. I have noticed corrosion and pitting on the transom mounted engine mount. (aluminum standoff on the stern). Some of the pitting is beginning to be significant around one of the thru hull bolts. I have several questions – My mechanic assures me that this is not an electrolysis problem – should I believe him? He has told me that he believes that around the late 80’s Grady had some issues with the mount, is this true? Does anyone know of a fix? Where can I find a replacement mount?

Thanks - Ross
 

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You've got a 22 year old boat used in salt water. Don't you think you should have some corrosion somewhere?
 

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I'm not a good mechancial advisor, but for the last several years, I go through and blast all corroded looking fittings, bolts, etc. with a rust dissolving solvent and give them a coat of something corrosion resistant, after years of neglect, resulting from leaving my marina to figure out what needed tobe done spring and fall. As Uno said, everything exposed to salt water gets a little ugly. Now how you separate ugly from failing, i leave to someone else.
 

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My boat is 22 yrs. old and has some corrosion. Use a power washer or a metal brush (no steel) to remove the corrosion and then put paint or whatever will keep the corrosion and pitting away. I know the GW owners will never do this but if you trailor the boat spray WD-40 on the spots every time before you have it in the water. If it stays in the water put grease over the spots. (Check because that could be construed as polluting the water). Good luck, Bob
 

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Discussion Starter · #5 ·
I agree there should be some corrosion on a 22 y/o boat and I am completely OK with that ( I have had boats of many shapes, sizes and materials for 30 years - I love older boats). The issue is that this has become significant over this past season and is an issue that has not presented itself to me like this before. The pitting has completely penetrated a 3/4'' piece of aluminum in one season. The boat was new to me 2 seasons ago. Some further research since the original post leads me to believe that the previous owner may have painted the aluminum with a copper based bottom paint the last time he painted it (in an effort to make it look good for sale - don't get me wrong, this is a well maintained and sound boat). Anyway the copper in the paint will react with the aluminum once the boat is placed in the water. So I have my fix and project for the winter, remove all the paint and apply the proper product...
 

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General corrosion probably won't eat through 3/4" of AL in one season...and I seriously doubt copper bottom paint would either. Electrolysis is my guess.

Can you post pics of the affected areas?
 

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Now matter what your mechanic says, laws of physics and chemistry never sleep. If you have stainless steel bolts (a very noble metal) contacting aluminum (not so noble) in the presence of an electrolyte (water, saltwater, humidity) electrolysis occurs. Think of it as a galvanic battery, electric current flows nonstop, electrons are flowing and changing the atomic makeup of the metals, unfortunately some oxidizing to dust like your aluminum. As hippie joe mentions, zincs which are even less noble than aluminum help. Bottom line is that the marine environment is tough on aluminum. If the boat lives in the water, you must be dilligent with your sacrificial anodes (zincs)

With steel there are secondary issues such as bacterial action which compounds oxide formation, then the question is is it a ferric or ferrous rxn?

Just when we think we got everything working just right, stuff like this pops to bring us back to reality.

Happy Holidays!
 

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ok... i had a grady(22'..1990) with the same bracket as yourn. factory coating started bubbling after some years of use. got so bad that all coating on bottom of bracket was completely gone. my solution: scraped off most all of existing factory coating to bare metal, removed zinc plate from bracket, and scraped underneath zinc to shiny metal. used muriatic acid to remove any oxidation on tne metal on entire bracket. primed entire bracket by hand with tnemec two part aluminum primer. you will not be able to get your hands on this product, but may find similar on internet. after drying for a day, applied two coats int/exterior enamel(oil-base), which is available at lowes, to entire bracket by hand, excepting where the new zinc is attached. leave that area free of any coating, attached new zinc , and this held for over ten years, and probably still holding. good luck!
 

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Discussion Starter · #10 ·
Thanks for the info....

:yes:
ok... i had a grady(22'..1990) with the same bracket as yourn. factory coating started bubbling after some years of use. got so bad that all coating on bottom of bracket was completely gone. my solution: scraped off most all of existing factory coating to bare metal, removed zinc plate from bracket, and scraped underneath zinc to shiny metal. used muriatic acid to remove any oxidation on tne metal on entire bracket. primed entire bracket by hand with tnemec two part aluminum primer. you will not be able to get your hands on this product, but may find similar on internet. after drying for a day, applied two coats int/exterior enamel(oil-base), which is available at lowes, to entire bracket by hand, excepting where the new zinc is attached. leave that area free of any coating, attached new zinc , and this held for over ten years, and probably still holding. good luck!
 

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that's a puzzler; mine usually are visually corroded after one season--not necessarily to be replaced, but the sharp edges are blunted
 

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I forget the exact formula but electron flow resulting from the electrolysis process is related to 1/r^2 ( some physics numbers over the radius squared) Thus corners with a radius, say raduis=.1 is a smalle number while a flat surface has an infinite radius (you know that when you are waking on the earth it seems flat, but there is radius, but it's a big number). Just think of 1/.1 vs 1/100000000000 the first is a large number and the second a very small number. I was interested in this subject years ago and I made an electronic device (based on a constant current battery charging circuit) that was used on shipwreck artifacts to reverse the electrolysis process. I played with some stuff at the Calvert Marine Museum in my days of idle time.

Anyhow, my attempt to explain science behind why the sharp corners erode first.
 

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This sounds like a marina specific situation where either through the fault of a boat that is plugged into the ac and has white and ground connected , or
the marina has the white and ground connected at the dock. Some people foolishly do that to keep the gfi's from tripping.
Also,
The best salt water resistant paint that I know of is neoprene based, like the red stuff that is used to under coat cargo trailers.

Dick
 
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