Uneven corrosion on trim tabs

LaRea

Does anybody know how the trim tabs on a cruiser are connected to the ground plane for corrosion protection?

During winter layup (my first with this boat), I noticed a big difference between my port and stbd trim tabs.  They are stainless steel tabs with a 3" circular anode bolted to the middle of the tab.  On one side, the anode was 50% gone, and the tab had heavy scaling and marine fouling.  On the other side, the anode looked essentially new, and there was almost no fouling on the tab. 

I poked around looking for a broken ground wire, but I could not find a ground plane connection to the tabs.  Are they grounded through the actuator?

Another possibility is that the previous owner accidentally used mixed anodes ... maybe aluminum on one side and magnesium on the other.  I replaced both anodes with magnesium, since the boat is now a fresh-water boat.

Handymans342

I would guess mixed anodes. Are the tabs all metal including the hinges? Are the actuators metal? Mine are Lenco so I think they are plastic actuators. Are they hydraulic? I would think they should be grounded if there is a metal fuse all the way back to current. Right? 

Cableguy Greg

I would also think that the PO mixed the anodes.

LaRea

Yes, the tabs and hinges are all stainless.  They have electric actuators, but I *think* the bottom end of the actuator is plastic, so no electrical connection through the actuator.  And I couldn't find any through-hull bolts in the engine room that could be bonded.

I guess I'll have to keep an eye on it this season and see how it does with proper anodes.

Black_Diamond

The tabs are not bonded. Take a real close look at the actuator on the one side and look for cracks, it can bleed current if so. I know this first hand.

LaRea

Interesting.  The actuator on the "good" side was replaced last year.  Coincidence?  Maybe.  

Handymans342

Are they Lenco?

LaRea

Yep, standard-issue Lenco.  

I should clarify:  the trim tabs are not actually corroding.  The one side has a lot of scale or mineral deposits or whatever it is -- a hard, light brown coating that can only be removed by scraping, chipping or sanding.  It's the same stuff I get on my stainless props every year.

Black_Diamond

If you pour The Works toilet bowl cleaner on it, all that brown scale comes right off.

LaRea

Thanks BD, I'll get a bottle of The Works and try it the next time I haul out.  I tried a similar product last year, but it was a fail.  

Handymans342

Since the Potomac is a toilet bowl, the Works seem appropriate.  Sorry LaRea I had to say it. 

LaRea

Hey, at least we have bigger snakeheads than other rivers ...

Handymans342

Those are good eating fish