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Outboard corrosion ?

Old 01-14-2019, 03:20 PM
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Default Outboard corrosion ?

What do you think is going on with the lower units of these Hondas? Left down in the water and starting to pit?


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Old 01-14-2019, 04:11 PM
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Have a look at the hull below the water line, it's the same, so there is a couple of options, electrolysis or normal oyster growth, my guess is the first one.
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Old 01-14-2019, 05:25 PM
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I see your from Australia...Do you have a opinion on the Noosa Cat?
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Old 01-14-2019, 05:27 PM
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ouchies
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Old 01-14-2019, 05:36 PM
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A pretty well respected builder, I don't think they have ever built anything that could be considered a lemon or just plain bad.
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Old 01-14-2019, 05:40 PM
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Thanks. I'm guessing if the problem is electrolysis than the inside of the lower unit is toast?
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Old 01-14-2019, 05:56 PM
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Galvanic corrosion affects the outside. They didn't do themselves any favors by leaving them tilted down - that seems stupid, unless they didn't have the ability to trim completely out of the water. If that's the case, don't buy it. If they had the ability to lift out of the water and chose not to, it makes you wonder what else they neglected. Also, bottom paint should never go all the way to the outboard's bracket - there should be a 2-3 inch gap of unpainted fiberglass where the outboard mounts.
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Old 01-14-2019, 06:02 PM
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Why the gap?
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Old 01-15-2019, 04:16 AM
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If you are not using aluminum anodes, change immediately.
Honda motors are "sensitive" to this.
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Old 01-15-2019, 04:22 AM
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From what I see, the white stuff is the same on the SS props, painted aluminum lower units, and hull. Thus would not appear to be galvanic corrosion, but better pics are needed.

I agree that the motors should not have been left tilted down. Foolish.
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Old 01-15-2019, 04:48 AM
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Look at the zincs on the exterior of the motors. If they are badly corroded it is galvanic corrosion,if not it is barnacles. i would bet barnacles from old bottom paint and no bottom paint on the the lower units.. Engines left in the water will get barnacle activity very quickly in warm water. Never leave them in the down position.
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Old 01-15-2019, 05:03 AM
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Maybe there are freezing conditions with the boat in the water. Then you need to keep them hanging in the water.
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Old 01-15-2019, 05:41 AM
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Better, up close pics needed....
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Old 01-15-2019, 06:50 AM
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Originally Posted by good stuff View Post
Why the gap?
Most bottom paint is copper based, so for drives that cannot be tilted out of the water (some outboards, all I/O's) you leave a a small unpainted strip to keep the copper away from the aluminum.

When I had an I/O that was kept in saltwater, it even mentions right in the manual that if you bottom paint it, leave a gap around the gimbal bracket. If it really wasn't that important, they wouldn't go out of their way to mention it in the user manual.

I looked around my marina, and over half the boats ignored it, then complain about corrosion. Most people who bottom paint boats never received any sort of formal training, but rather learn about it from watching other people.
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