Yamaha 9.9 corrosion

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Yamaha 9.9 corrosion

Postby D&D » Mon Jul 17, 2017 8:19 am

hi all - i have a 1993 pdq36. I have been lifting the yamaha outboards out of the water when under sail or at night, to hopefully minimize corrosion. In fact the opposite happened and the lower leg of each engine has rusted through. Wondering if this has happened to anyone else. I cant figure out why it happened but when I lift the motors the part that you can see in the pictures does slightly dip in the water - the motor doesn't come all the way out - but the zinc anode is not in the water anymore as it is higher up on the shaft, so I am thinking maybe I should have left the motors in the water and allowed the zinc to work. Either that or I have an electrolysis problem on my boat or maybe there was a problem at a marina I was in. I've attached a picture of the corrosion. Has anyone else ever had this problem? I have the lower legs on order and am hoping that I can avoid this happening again. I hauled out in Stuart Fl and inspected in Feb and everything looked fine - not sure how i could have anticipated this. Am currently in the Rio Dulce. Thanks.

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Re: Yamaha 9.9 corrosion

Postby thinwater » Mon Jul 17, 2017 8:29 am

a. You are NOT getting the engines all the way out of the water. When I switched to the new engines I noticed that they would not lift clear unless I cut part of the battery shelf away. Perhaps you can do something similar. The PDQ 36s do sit lower than the PDQ32s. They should be 3-4 inches clear at the dock.


b. You probably have stray current. I noticed when I hooked up the new engines that if the power was on there was a substantial DC leak to the water. I had to change something on the wiring harness, but I can't remember what. it was.

The best idea is to get them clear. Then you have no metal in the water = no stray current problems. Also faster under sail!
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Re: Yamaha 9.9 corrosion

Postby Root » Wed Jul 19, 2017 5:24 pm

I might add from your photo, that the zinc anodes mounted under the engine cavitation plate are completely gone. An indication that there is strong electrolysis taking place probably from, as mentioned, stray current. You can check for stray current by placing the leads from a voltmeter in the water and reading the voltage. Ray

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