1968 200/20hp, is the Anodic Plate needed noticed mine missing

[charly1954]

I've had my motor for 20+ yrs and never notice this plate. I was going to change the impeller and notice a loose screw hanging right above the prop. I looked it up on the net and seen the plate was missing. No idea if it was ever there when I bought it 20+yrs ago. I did have the impeller replace shortly after I bought it, maybe the mechanic didn't put it back on. Anyway is there a real purpose for this plate I can't see having one. Right next to it there is a nut/bolt that holds the lower unit gear housing.

 

[ThomW]

Boat anodes protect the metal parts of your boat or motor from galvanic corrosion, which occurs when any two dissimilar metals are physically or electrically connected and immersed in water. Basically, it is meant to protect your engine from corrosion. It will corrode and need replacing so your motor doesn't.

 

[charly1954]

Thom I added a photo, I dont' understand how anything will get corroded by it missing I don't see anything it protects. The replacement plate doesn't show any gasket to seal anything so it looks like water could get thru the plate and the plate itself actually looks like it has a drain hole. Here's a link showing the plate

https://www.boats.net/product/mercu...&utm_term=47820A1&utm_content=Med AOV Parts 1


Here's a photo showing the missing plate. I put a couple nuts on the screw that holds the plate.

 

[ThomW]

Charly, it isn't like a cover to protect what is underneath it.
The anodes are made of aluminum or zinc.
When an outboard motor (metal) is in the water (an electrolyte), it produces small amounts of electrical voltage. When there are 2 different types of metal in contact (and in a electrolyte like water), like the metals making up your motor, they act almost like a battery. The less noble metal (your propeller or other parts) becomes an anode of the battery and the more noble metal (your steel shaft) becomes the cathode. The electricity flowing through the metals will damage the less noble metal.
The purpose of a sacrificial anode is to add a 3rd metal that is more active than the others. The most active metal (your anode) becomes the anode and sacrifices itself to corrosion to protect the other metals. Hence the name sacrificial anodes. You can buy a new one for around $10. I would say its worth it.

 

[jbcurt00]

Mercury sacrificial anode plate used on 1967-1980 20 HP models

Well, Mercury thought it important enough to install on your motor...... sacrifical anode plate as ThomW suggested

 

[charly1954]

Tks for the added info. No disrespect meant but your first reply I thought you meant it protected something from getting wet. With your 2nd reply I now understand what it does. And the reason mine is missing is it corroded and fell off. No telling how long its been gone but I'll be getting another. tks for the help guys

edited, Question guys: It looks like they are made of zinc so if I had a small plate of zinc, drilled/taped it and attached where this plate goes then would that work? I don't see any for $10, $25 and up is what I'm finding online

 

[racerone]

Not really a needed item unless motor / lower unit is submerged at the dock all the time.-----Needed more in salty / brackish water.----If your boat / motor lives on your trailer that item is not needed.----Yes you can fabricate one.

 

[charly1954]

It on the trailer and in water 2-3 days a week and average about 6hrs/day. So average maybe 15hr/week and it runs maybe 20-30 mins a day so lucky to run the motor 1hr/week. Since Thom said its the electricity running thru the metal that can cause corrosion then running it 1hr/week I would think not corrode much. Its pull start so its not hooked up to a battery. With that said I'm gona put one on it is a 50+ yr old motor.
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TKs all for the input its appreciated.