Cap'm Kurt

Anyone ever experience this type of corrosion? At the nylon fitting where the trim tab postion indicator cable goes thru the alum plate. The corrosion has eaten enough alum to create this hole next to the nylon fitting.
This started while using in the summer but i have completely cleaned it out, used OSPHO, filled it with JB Weld, and repainted it twice.

Keeps coming back, even sitting in the shop after having parked it for the winter and cleaned, filled and repainted it again. Over a couple months it builds a big ball of corrosion were the hole is at.

The trim tab on the other motor does not do this at all, but i did notice some filler and repaint at this same spot on the other trim tab.
See pic below.




trim tab transom plate corrosion

scarabman

iTrader: (1)

Yes, I have had a similar problem in the same spot. You are probably not getting all the salt cleaned out due to restricted access. In order to fix mine, I pulled the tab and ground off all corroded/pitted material and then reshaped with epoxy paste. Never came back.

FYI, you likely need new cable seals, and/or need to torque up on the packing nut because water get in through there is probably what started it.

Cap'm Kurt

SM,
That just might be it. I thought i cleaned the hole out well, but i did not have a spare nylon cord fitting, and it was crossthreaded when i got it, so i did not unscrew it from the alum mounting plate to get to the 1/2" threads in the mounting plate. Its off now so i can do a better job of cleaning around the threads too.

I'm hoping not to have to pull the whole tab like you did, so i will try this first. If does it again i'll pull the whole thing. Hopefully, the corrosion is not between the mounting plate and the transom. Rest of the drives almost no corrosion.

Thanks for info.
Kurt

FBRONCO

iTrader: (1)

Mine
I just took mine off because of a similar issue. My is corroding from the back from that area. But mine has stainless fittings going through it. I thought it was happening because of the dis-similar metals.

Cap'm Kurt

Fbronco, I've seen boats with SS fittings on the cables and no corrosion even in brackish water. I think its more of a matter in this case on having everything sealed. Threads, rubber grommet in the fitting, all around the trim tab mounting plate to the transom, and bolts so water doesn't get behind it. In our case with the holes on the side of the threads, i think it was the threads and grommet leaking a little water.

Cap'm Kurt

For your information, that Mercury fitting is way over a hundred bucks. After market from marine stores about $50 to $60.

I believe in OEM stuff sometimes due to quality but this is a little extreme. I found a Hubbell brand for $10. The Hubbell looks a little stronger than a couple other brands i looked at. It's a 1/2" Mnpt x (1/4" to 3/8") diam , cord connector, nylon. See attached picture.

FBRONCO

iTrader: (1)

It's possible, but I've looked at a lot of used boats in my time and almost all of them seem to corrode in that area where the indicator cable comes through. Many years ago there was an article in power boat magazine that described installing k-planes on a boat with pictures and illustrations in a step by step format. I believe the boat was a formula. Anyway, they only put sealant around the through hole openings on the mounting plates. They did not seem too concerned about sealing the whole plate to prevent water from getting behind it. But, like you - on my last two projects I put sealant everywhere, even along the whole edge of the transom plate. With these I'll do that and also put sealant on the threads of the hydraulic through hull fittings on the transom plate and the bolts and washers.

scarabman

iTrader: (1)

The one I had trouble with was completely sealed to the transom, full coverage on the backing plate as well as all mounting bolt holes were sealed under the bolt head. Water was definitely getting in through indicator cable fitting and rotted inside and around the back of the plate.

Cap'm Kurt

From your info, it makes sense that even if the fitting seals good on the threads and the grommet seals, water can still get in to the backside of the alum threads from behind the transom mounting plate if the thru hole is not sealed. But since my fitting was cross threaded and not sealed, I'll replace and seal the fitting good this time and see if it cures it. If not, pull the tab transom plate and reseal everything.

Something so easy when it's put together, but not many people, especially factories, are going to seal all the pieces right the first time. Just doesn't happen.

FBRONCO

iTrader: (1)

I totally agree. And it happens with most manufacturers. A lot of builders talk about boats being hand built like it's a good thing. But it's really only as good as the people you have working on it that day. I think that's why the really high quality boats cost so much money. You really have to take your time and be meticulous when building these things. What if the worker has a hangover on the day he or she is mounting the k-planes. Once they are on, you will never know until years down the road. The builders need a good set of checks and balances and audits to make sure they are putting out a good quality product.