Transom sheetmetal pitting and small holes

[dmdc]

I am going to ask another question that has probably been answered, I just didn't really see what I was looking for. I have a '87 Sylvan Super Sport, owned for 12 years. Ive noticed corrosion bubbles on the exterior of the transom, I have put a sealed stainless screw in them in the past. Took it a part to find the wood was wet but not rotted yet, but the metal that had contacted the wood transon was extremely corroded. By this I mean surface all the way to mostly (many)small diamter very deep pits to a few large diameter areas that I broke through the panel pits. I am an ex-airline sheetmetal guy, I can handle the rapairs, but, in this case, should I scab in the entire transom, riveting to the outer 2 inches of the origianal transom? Or as I've seen here Glove-it. I don't want to do this again in 5 years when these pits resurface. Any help would be appreciated.

 

[Capt'n Chris]

Re: Transom sheetmetal pitting and small holes

You should find the culprit of your electrolysis problems and arrest it.

 

[Azonic]

Re: Transom sheetmetal pitting and small holes

Is it possible the wood in the transom is pressure treated?

 

[reelfishin]

Re: Transom sheetmetal pitting and small holes

Is it possible the wood in the transom is pressure treated?

That's the same thing I was thinking, could the boat be built prior to the knowledge that PT wood attacks aluminum?

It could also have had some saltwater trapped in there over the years?

Without seeing it first hand its hard to say what my fix would be. If the overall panel isn't compromised so bad it's unsafe, I'd consider filling the pits with epoxy and then a coat of gluvit and some heavy epoxy paint to be extra safe.
Then a fresh, epoxy sealed transom panel.

 

[Bob_VT]

Re: Transom sheetmetal pitting and small holes

Sand the aluminum and use gluvit. It will create a barrier layer that seal it up. You might even do 2-3 coats since it is a vertical surface and it is very thin when applied.

Yes it sounds like salt corrosion that has attacked to metal.

 

[dmdc]

Re: Transom sheetmetal pitting and small holes

As far I can tell the transom is not green(pressure) treated. I bought the boat from the 2nd owner, between the 2 of us this boat has not been out of the upper midwest(MN), so salt is highly unlikely. Electrolycis(?), all eclectronics are wired with ground wires directly to each, with the exception of the am-fm antenna, it is mounted to a console top. I found the splash well leaking about 10 years ago, siliconed it up, only to find it leaking again. Hard to silicone when there is dirt and oil in the area. When wood rots you must get a chemical reaction with the metal of some sort, so I figure thats why we have corrosion. As far as the replacement transom, would a piece of microlam header material work? They are exterior glued and the right thickness and close width. Thanks for the help

 

[Bob_VT]

Re: Transom sheetmetal pitting and small holes

Or it is a result of galvanic corrosion from dis-similar metals...... the electrical field is a good guess too........ regardless of fault it has to be repaired.

I would still seal up the microlam the same as plywood and yes it should work fine if you have it on-hand.

 

[dmdc]

Re: Transom sheetmetal pitting and small holes

Ok if anybody is interested I was able to get some pics maybe this will help. I think the transom was pressure treated, The only place there is corrosion is where moisture was held in contact with the metal.

 

[sprintst]

Re: Transom sheetmetal pitting and small holes

I filled some small pits from battery acid eating at the hull in the back corner with Gluvit...but that was a horizontal surface. Gluvit will run as it's quite thin depending on the temp.

Whatever you fill it with if you give it a couple of thin coats of Gluvit to build up the thickness you should be good for the next 50 years. I don't think I can even scratch through the Gluvit if I wanted to.

 

[dmdc]

Re: Transom sheetmetal pitting and small holes

A little update on the repairs. After reading many post, I have got the new plywood transom cutout and glued up. The micro-lam didn't pan out, it had a waxy coating from whatever so I passed over it. I went to A west Marine store and talked over what I was doing. Came up with using West system 105 epoxy and 206 hardner for coating the transom wood and a couple coats on the sheetmetal after I install a 13.5"x62" full external doubler. The material loss isn't enough to jeprodise safety, I just don't want to chance corrosion surfacing again and wrecking my neat looking repair job. I worked in aviation on a structures crew for a few years, so I know what I'd do for aircraft, but the boat doesn't fly at 30k! I think I found a legit median here. The flotation foam is dry but I don't like how its formed to the hull and every part, this gives water a place to sit. Is the foam a structural component? I left the front half in place, may replace the rear with sheet stock.
Thanks for the advice and great website.