Martyman
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Aluminum Boat-Zinc Chromate coating?
Hello;
We just bought a 1993 16 foot Bayrunner for Baja. It will only be at mooring and being used 1-2 months a year. Do people coat their hull with zinc
chromate to minimize corrosion for that little time in the water?
Can't wait to get it down there!!
Thanks,
Martyman
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comitan
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Its my understanding that Zinc-chromate etches the aluminum for painting, this what I have used it for in the past.
Strive For The Ideal, But Deal With What\'s Real.
Every day is a new day, better than the day before.(from some song)
Lord, Keep your arm around my shoulder and your hand over my mouth.
“The sincere pursuit of truth requires you to entertain the possibility that everything you believe to be true may in fact be false”
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Diver
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My 1992 Lund has been scraped and pulled over so many Baja beaches that I can't remember them all. When it's not in Baja sitting in the water or on
the beach, it is sitting outside on its trailer or crabbing near the Oregon coast. I rarely wash the Baja sand off it until months after I get home.
Bottom line - no corrosion problems at all !!
Just some dings and dents and Baja sand ! 
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losfrailes
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About the only time you need zinc chromate is for a primer if putting some antifouling paint, like copper or tin based, on it to provide a barrier
coat.
If you pull your boat frequently and therefore keep the baddies from growing on there, no need for antifouling paint, i.e., no need for zinc chromate.
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Barry A.
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Alum. boats WILL corrode, and it usually happens when you least expect it. I had one disintegrate in my garage at Nags Head, NC were we lived about
200 yards from the surf.
The insides of many aircraft parts (wings, fuselage, etc.) are often painted with zinc Chromate. It serves both as a primer, and as a corrosion
inhibitor. The inside of wings and fuselages are rarely painted----they are left only with the zinc chromate on them.
I had a seaplane that had only zinc chromate on the inside of it's belly, and as long as I washed it with fresh water everytime I landed in the ocean
it was fine------forget to wash it and the corrosion would start it's insididious work.
I recommend zinc chromate-----both inside and out, for any aluminum boat that you cannot watch and take care of regularly.
Barry
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backninedan
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Diver
I have a Lund here in Loreto and so far it has been a helluva boat. I watch close for any signs of corrosion, so far...nada, and its over 10 years
old.
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Cypress
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Aluminum makes it own sheild, it's called aluminum oxide. Sorta like rust, but grey in color. Looks just like aluminum, it makes a barrier between the
metal and the water/air. That's why aluminum boats and anything else made of aluminum lasts.
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Barry A.
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Based on what you guys are saying, I wonder if the "newer" alum. boats have some sort of clear protective coating on them. I have a 35 years old
alum. canoe that has spent it's life in the desert and semi-desert and it has some serious corrosion pits in it, especially on the inside------they
just seem to "appear" when I am not looking.
Also, both my Gregors have millions of pits in the Alum., some pretty serious. The Gregors are very old also.
I have never put any kind of coating on them, but I do wash them with fresh water and a brush pretty regularly. All these boats are outside upside
down.
What you think???
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Diver
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I would think that if you coat the alum, you are defeating its ability to form an oxide layer - no corrosion.
If it leaks air it will form a layer beneath the coating and then you have nasty peeling that will never stop. Like an old house; you have to
completely strip and start over.
That way I look at it, with boats like my Lund and your Gregor lasting well over 20 years with no corrosion protection, it doesn't seem worth the
possible headaches and costs to keep a coating intact, especially if you beach/launch/scratch.
Besides, I deserve to buy myself a new boat at least once every 20 years !!! 
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backninedan
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I have a friend with an aluminum boat and the stern needs some repair work. Can it be done with fiberglass? I have experience in laying glass and
the repair would be simple. I just don't have any idea on how well the two materials will bond. Anybody have an answer??
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Barry A.
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Diver-----
You have a good point there about "nasty peeling" of a paint layer. I have noticed that both my canoe and the Gregors have a "tough, rough coat" of
some kind of paint that was sprayed on the insides of the hull, presumably to reduce the slipperyness of them, and now it is beginning to peel off in
an excellerated manner----once the paint is breached, it does not take long for it to exfoliate. Considering that all my alum. boats are ancient, I
guess I am lucky that they lasted as long as they have.
They all still do their job, so I won't be replacing them any time soon, tho.
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Martyman
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Well...
Thanks all for the advice. I will probably not coat it because basically I am a slacker. After all I probably need a new/used boat after 20 years
too!
Thanks again,
Martyman
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Diver
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| Quote: | Originally posted by Martyman
Well... I will probably not coat it because basically I am a slacker. |
An honest man with an honest reply !
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Hook
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The best preventative against corrosion on your aluminum boat is to disconnect any battery you have on board after every use. Reduces the occurance of
electrolysis from stray current moving through the hull. Also, charge your battery by disconnecting it from the leads to the boat........or remove
from the boat altogether.
Wire any bilge pump(s) directly to the battery so they are always able to draw, especially if on a float or water sensor switch.
You should be more worried about corrosion at welds than the exterior or interior of the hull. That's where to inspect.
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Pescador
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The most important thing on an aluminum boat is to make sure that you sacrificial anodes are complete and in good shape. Usually there is one in the
area where you bolt to the transom and is generally u-shaped, the second one is generally your trim tab and is located just above the propeller. It
is imperative that you check these regularly and replace frequently if you are going to moor in the salt water.
In warm water, like over 80 degrees F it is a good idea to pull your boat at least every 10 days and let it dry out for a full day which will
inhibit growth and barnacles on the bottom, in cooler winter water this can be done once or twice a month. You can jump in with a mask and fins and
scrub the bottom with a good stiff brush if you choose but it is almost impossible to get off everything and there will be hidden areas that will
occasionally require more attention.
I have seen some aluminum boats that were painted with Zinc chromate and then painted with anti fouling bottom paint. My best assessment is that it
sort of works and still requires some maintence to function. We had a guy at San Lucas Cove that used some of the really nasty stuff they still sell
in Ensenada but we noticed the crabs kept dying around his boat.
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Martyman
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That nasty stuff was probably tri butyl tin. They've taken that off the market in the states a while back. They were noticing sea otter mortality
near the one boat yard that was applying it.
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