Zinc replacement

[wlewis]

I have a 2011 model Freedom 225 with an aluminum bracket/platform. I bought it new in 2013 and have always kept it out of the water on a JetDock. Boat probably has less than 200 total hours on it and is seldom left in the water overnight. During recent servicing the motor, I noticed the zinc on underside of the bracket had a fair amount of corrosion on it and though still intact and more or less the same size as when new, I thought I’d replace it. When removing it, I noticed the bracket itself has started to corrode where the zinc was attached. I ground down the corrosion best I could and am in the process of priming and painting the affected area and replacing the zinc.
Now that I think about it, I’m wondering did the zinc cause the corrosion on the bracket? Since the boat stays on the JetDock and and spends very little time in the water, do I even need the zinc?
Anyone here have any thoughts?

 

[seasick]

Not sure what you are painting but NEVER EVER paint or prime the area under a sacrificial anode.There has to be good electrical clean metal to clean metal contact.
Zincs wear out and loose their effectiveness over time. If you had the same zincs for 10 years, you are luck you still have a motor
The only sure way to know when it's time to replace zincs is when they weight 1/2 or less than when new but who actually does that.

If you boat in fresh water, zinc is not the required anode metal

 

[wlewis]

The bracket had factory paint under the zinc. Note the picture. The old corroded zinc still retains the original size and very close to the weight of the replacement.

 

[Halfhitch]

The bracket had factory paint under the zinc. Note the picture. The old corroded zinc still retains the original size and very close to the weight of the replacement.

Like seasick said, before mounting an anode onto the bracket, any coating must be removed down to the bare metal so there is perfect continuity between the anode and the object it is protecting. The fact that there was no continuity between the anode and the bracket is why you see deterioration of the bracket and not the anode.

 

[wlewis]

Good point, but I don't understand why it was painted at the factory.

 

[wlewis]

Armstrong bracket rep says paint it because continuity flows through the attachment bolt secured with a nut and star washer on inside of bracket.

 

[Halfhitch]

Excuse me, I thought we were talking about the Yamaha tilt/trim bracket. I will shut up.

 

[glacierbaze]

How Do Sacrificial Anodes Work?

The way to counteract galvanic corrosion is to add a third metal into the circuit, a sacrificial anode, and often that is zinc.

www.boatus.com

 

[DennisG01]

Correct - the bolt/thread connection makes a perfect continuity. Paint it.

Edit... just to add... this is assuming the contact between the bolt head and anode remains good. Hence the reason to check them on a regular basis.

I "suspect" what you might be seeing there is not so much corrosion, but "paint lifting". Meaning, the edge of the paint near the hole is very thin and salt water could work it's way in there and eventually get between the paint and the bracket metal and start to "lift" the paint off... then that continues and continues.

If it was me... I would sand really well and then cover with epoxy resin and then paint.

 

[wlewis]

I've ground it down to bare metal best I can, coated with epoxy primer and will top coat it with matching Imron.