Corroded trim tab mounting screws

R

ripple

New member
I have kept my boat in the water almost full time for the past year and for the time that I have owned it prior to that it was only in the water for a maximum of a week at a time. Prior to moving it into a full time slip, I applied 4 coats of epoxy barrier and 3 coats of bottom paint. I also removed all of the below waterline hardware and over drilled the holes and filled with thickened epoxy. I have pulled the boat out for maintenance, oil changes, etc. and never noticed any problems.

Today, I pulled the boat to drill some holes to install a transom mounted bait tank pump. I brushed off some growth on the trim tabs and I was surprised to see visible rust on 3 of the mounting screws on the port side trim tab, as well as stains branching out from the screw on the stainless steel plate. I have seem this happen before on other boats I have owned and it is almost always as sign that it is substandard stainless, definitely not 316. Thinking I had caught it in time, I went to back out the screws so I could get some new ones and the heads of 2 of them twisted off completely - there was almost no metal left below the screw head.

As far as I know, these tabs were installed by the factory (my boat is a 2006 model). I have read all about the recent sale of the remnants of the company, etc. so not really anyone to complain too as far as workmanship anymore. I guess posting this is more of a heads up to other owners of boats of the same vintage to inspect your hardware and check for similar problems.

I posted some pictures and you can see that there are 3 of the 6 screws on the port trim tab that show no signs of corrosion, and 3 of them are clearly not good stainless. This is totally unacceptable in my opinion, definitely does not inspire confidence in the workmanship of the boats built during this era.
 
Ouch :cry

I'd have guessed galvanic action until I saw the zincs on your trim tabs. Is there a good clean connection between the zincs and the tabs? Any paint in that joint? I would have expected to see the zincs a little eroded at least. Would be a good idea to have a ground wire from each tab, somehow to the engine ground.

Not sure that's it but it's one possible explanation.

Charlie
 
Charlie - interesting theory with the galvanic corrosion. I had considered that too, but it would not explain why 3 of the screws with the same ground path to the zinc are completely fine. One slip that I was in was fairly "hot" and the zincs were eroding really fast but I moved about 6 months ago and since then the zincs have not been burning up so fast.
 
I have an 06 model as well that stays in the water most of the time, but no sign of corrosion...yet. I just added the zincs to the plate this spring as a precaution.

Let us know what you find.
 
Ripple, I had the same problem with my Lenco tabs this last winter. The Lencos come with the mounting hardware as I think the Bennetts do, so I don't think that this is a C-Dory problem. You might want to call Bennett, as you still may be under their warranty. Problem is, I think they cover everything except galvanic corrosion.

It may be that the reason the corrosion is not uniform across the mounting plate is in the way the mounting plate and the tab (where the zincs are mounted) connect to each other. It is not a "solid" connection in either the Lencos or the Bennetts, especially the Bennetts. Just a guess.

I included some pictures of the difference in the screws from the same plate, and the extractor that I used to get the broken screw out of the transom. It is called an "Unscrew-Um" and it worked very well. It "captures" the broken screw and then backs it out.





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Robbi
 
Robbi,

Thanks for the advice. That is a cool extractor - I've never seen one like that before. I already reinstalled the tabs so I am not really worried about making a warranty claim or anything, I just wanted to make people aware of this potential problem.

I understand that there is not an optimal ground path from the main tab to the plate that screws to the transom, it just seems suspicious that there could be a good screw surrounded by 2 that failed. Perhaps running a ground strap from the zinc on the trim tab up to the mounting plate would be a viable solution to prevent the same thing from happening in the future. I plan on at least visibly monitoring the screw heads more often now.

-Dougal
 
Just ready to remount our tabs after an issue and the old screws seem large at 1/4 including threads by 1.25in long. Thinking of using 3/16 by 1inch long instead into the epoxy plugs. Too small?

Greg
 
On my Lenco trim tabs, I am finding rust, not on the screws, but on the welds where the tab is welded to the hinge plate. :( I have just taken some photos and expect to send them to Lenco. The rings where the welds are have concentric rust rings, on some of the welds. It was a a surprise to find that they are made made of 304 Stainless, electro-polished, not 316.

The screws all seem to be OK.

Harvey
SleepyC :moon

Friends_Cal_09_10_Oct.thumb.jpg
 
I have a question about the corroded and now broken off screws. We just purchased a C Dory 25, and it was delivered yesterday after dark to us in Bellingham. The driver noticed that the zincs on the trim tabs were almost gone, and there was a little corrosion on the screws. I replaced the zincs, and used a wire brush to clean the screws up. Two of the screw heads came off, but the rest appeared good. We had to go ahead and put the boat in the water because of the time of day. I know I will need to fix this when we haul in the spring to paint the bottom, but will this be an issue now? The boat will be kept moored in saltwater. Would it be a good idea to try to use a sealer compound over the holes, if I could find one that would work under water? This is all kind of new to me.

Doug
 
Doug,
Congratulations on the "new" boat.

I assume that you have read this older thread, and know that it is preferred to overdrill the holes for the screws for the trim tabs, undercut, fill with epoxy, then put the screws into the epoxy plugs. Many boats have not done this, and many have either found very minimal core issues, or none--because there may not be core material down in this area. I don't know exactly how your transom was made. My 25 did not have core into this area, but I did clean it out, while I was doing other repairs.

I would also watch the tabs carefully during the time they are in the water. The SS may be a different alloy in the screws. They may be Chinese screws.

There is no really good underwater sealant--althugh many have been tried.

I have found that "underwater" epoxy works fine--and put a fair amount on a damaged keel on a large sailboat. It had adhered well to the area which had been sanded with 100 wet/dry sandpaper, and held in place with wax paper, backed by cardboard/plywood /Spanish Windlass to push it up agains the keel. When around out 9 months later, the epoxy had worked its way well into the cracks. I also used underwater epoxy to repair the trunk on a sailboat with a lifting keel.

JB weld, makes "Water Weld" I have used this on several applications, and think it would be your best bet. Just mix up a small bead of this (roll between palms) and push hard into the areas. You will be able to get it out in the spring--if it does not pop out, you can always use a Dremel tool.

Below is a photo of how I opened the area along the plywood and bottom interface, where the trim tab of my 2003 25 was screwed. The tab area did not have rot, the area of the drain and transducer did have some rot, and was easily repaired.

2007_05_23_002.sized.jpg
 
Bob,
Thanks so much for the information. It sounds like it may be okay to wait until spring, when we haul out. (We don't have a trailer.) This boat is a 2008, and I don't know how the transom was built. I may try the Water weld, as well.

It is so nice to have a place to go for information. We have had sailboats for 20+ years, so my knowledge is limited with C Dorys, and outboard boats.

Thanks,
Doug
 
My trim tabs are screwed on with screws that have become rusty.
The boat, a 2005 ProAngler, was in a Fla. salt water harbor for 4 yrs. and then on my trailer in Alaska for 6 more yrs.
Several of the screw on the port tab are rusting but not all of them. The stbd side is rust free????.
I will attempt to remove the screws in the spring. It is 13F right now and screws are not a problem at this time.

Happy Thanksgiving to all..........

Jack in Alaska
 
Stainless steel can suffer from what is termed "crevice corrosion". It often occurs under the head of screws and bolts even when the threads and bolt head are sealed water tight. It does not require oxygen or the introduction of any corrosive element.

This is a familiar problem to some owners of older sailboats. Often the keel ballast was attached to the hull with large stainless steel bolts. Even when sealed from salt water contamination they sometimes corroded to a dangerous point.

You can read about it if you google "British Stainless Steel Association" and "crevice corrosion".

Regards, Rob
 
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