I spoke with IMCO yesterday and they said it was cavitation burn after they looked at these pictures. Somehow the water coming off the hull and/or extension box is causing this.

So is there a fix?

I also thought it had something to do with electrolysis since it was close to that plate. But when it was taken out the water after three days there was no material or white flakes in the area like on the cathodes.

So is there a fix?

Here is a picture of everything with the drive down.

Any suggestions on what could be causing this or how to fix it? Or, is this really common and I shouldn't worry about it?

Thanks

I disagree with the cavitation burn, I've had cavitation burn on both outboard lowers and my B1. Cavitation burn is caused by extreme low pressure, so you wouldn't see it on a leading edge. It's much more common at the rear of the drive close to the prop and on B1's it's more common on the skeg. How fast do you run?

Strange place for cavitation burn. You could try sharpening the leading edge like this:
http://i763.photobucket.com/albums/x...s796Medium.jpg

Thank you for the reply guys. I am not running all that fast, 68-69. The first time I noticed it was after a poker run on Lake of the Ozarks.

What could have or is causing this? Could it be electrical?

Also does anyone have a picture of cavitation burn?

What would be the best way to sharpen the leading edge (tools, cutting)? The last thing I want to do is F it and cause a bigger problem.

Were you running a lot of trim? Could the trim angle cause the low pressure area?

I do have to run a lot of trim to get the bow up. The prop is out getting re-worked hopefully this will help with the bow lift.

Your running that drive too deep - I would raise the drive. It will improve your top end and the boat will handle better at speed because you won't have to trim as high.

This is cav burn on an Imco shorty. I worked mine with sanding discs and scotchbrite discs with an air grinder. Then I went over the whole thing with sandpaper. I also welded up 3/4 inch of the rear of the water inlet and opened it up to the front. I added a slight bevel at the rear of the inlet to lower water pressure and stop the cav burn. I'll try to attach a pic of a Wilson blueprinted lower also.
http://i763.photobucket.com/albums/x...s750Medium.jpg
http://i763.photobucket.com/albums/x...oblueprint.jpg