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Letter 31788
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++++ Hello Jim. Sorry for the tough times down there. Do you have any knowledge about the aluminum, such as whether it was anodized, chromate conversion coated, or clear coated?
++++ Luckily I have never been in a hurricane, but I nevertheless sympathise with your plight. I wonder if the rain you experienced was high in salt water from the ocean and this has caused the aluminium to corrode. Your description is very close to how I would describe the corrosion of unprotected or poorly protected aluminium. I cannot think of a way of recovering the surface unless you can get the boats rubbed down and then correctly treated. I would suspect a good anodising process should be what is required. Alternatively, try claiming on your insurance.
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from Amazon |
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++++ Pitting corrosion is the most common corrosion form seen on aluminium. It starts from a weak point in the oxide, and after initiation, the reactions within the pit will reduce the pH and increase the chloride concentration and in this way sustain the reaction. Pitting can penetrate several mm during a short period if the conditions are extremely unfavourable. Normally the development of pit depths follows a time function of the form: D = K · tc Where D is the depth of the deepest pit, K is an alloy-, surface area- and environment-dependent constant, t is time and c is an environment-dependent parameter which often is close to 1/3. For good alloys immersed in sea water, with t given in years and D in mm, K can typically be close to 0,75. The development of the maximum pit depth will typically follow the form shown below. Typical development of pitting corrosion rate, the figures on the axes are only examples. [34]. with a rapid increase after initiation followed by a slower growth. The pits can be of different shapes, wide or narrow. The narrow pits can often be dangerous because the attack can be deep and difficult to detect. The susceptibility to pitting corrosion depends on several parameters. Michael Balda
+++++++ Other threads did not really answer any of my questions.
My 24' anodized aluminum pontoon tubes on my '89 Harris
pontoon boat started oxidizing 2 years ago. I live on a
small inland lake in SE Michigan. First, I need ideas on how
to remove the oxidation which is causing pits (local boat
dealers do not have barnacle remover only "Zing" and like
items that contain muriatic acid which etches the aluminum
(local boat dealers have never seen oxidation that resulted
in pitting and have no ideas on what to do about it).
Second, on sealing the toons for the 4 months its in the
water. Is anodizing/chromating/clear powder coating easy to
do with the toons still connected to the boat (any estimate
on costs for each method)? Third, I need ideas on preventing
the oxidation, I do not have anything to bolt-on an anode to
the toon (a anode company suggested using magnesium) but I
guess I could have something welded on. Any ideas for a
electrical device that would protect the toons. I am hoping
not to spend countless hours or money cleaning, polishing
& sealing these are 24' long and are summer's are
short. Scott Warner |
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June 17, 2008 Hi, Scott. I would go ahead and get magnesium anodes from a boating store . . . , , , because they are very important. Maybe you can clamp them on with a fiberglass C-clamp? Anodizing is usually a tank process, not something you can do while the pontoons are connected to the boat, but you do a clear coat with them still connected to the boat. Regards,
August 6, 2008 Hi Jim, We eliminate this kind of damage from ever happening by
applying a coat of Sharkhide Metal Protectant at the plant
level. but some manufacturers can't do this so the next best
thing would be to apply at the dealer level. If you were to
apply a coat to your boats as they arrive, they would not be
effected in any way by salt spray. The bad news is the spots
you mentioned on your boats are most likely tiny pits in the
surface. It would take a tremendous amount of grinding and
polishing to remove them. Although Sharkhide won't remove
them, it will work wonders to camouflage them. Once you've
applied the Sharkhide you can still notice them when you
look straight at the pontoons (@ 90 deg), but as you begin
to look down the length of the boat, the spots will disapear
and it will have a wet reflective look.
Dear Reader, please --
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