Transom repair/replace/scrap?

[chavycha]

First time posting here. Lots of reading so far. Great inspiration on this forum.

I recently bought an old Valco Bayrunner hull to fix up. I got it knowing it was going to be a project. We go to Baja every year and the combination of the high bow and wide beam, while still being lightweight, is pretty near perfect for our use.

The previous owner(s) had done some work on the hull; none of it good. The seats and transom had been replaced but they'd been done with crap plywood, and unsealed at that. So naturally my first step was to take out the approximately 500 pounds of water-logged ply. Yuck. The good is that everything under all that looked pristine. Not a single cracked or broken weld forward of the transom.

The same guy(s) had also 'repaired' the transom. There had obviously been a corrosion issue - and the 'solution' was to weld another sheet of aluminum onto the outside of the transom skin. When I pulled the transom ply I found some pretty extensive corrosion on the inner (original) skin. The outer (new) skin appears to be in decent shape, at least from the outside. I think it's .125" plate. The interior is significantly thinner, I would guess .060" or .080".

I'm worried that there is corrosion and water trapped on the back side of the original skin and that'll eventually start eating the new one.
Not sure how to proceed from here. I'm pretty handy but I haven't done any work with aluminum and I don't weld.

Part of me says clean it up, spray it liberally with CorrosionX, put down a new sealed plywood transom, and call it good.
Another part of me wants to cut out all of the 'repair', then take it to one of the aluminum boatbuilders locally and have them put a proper transom on it. I don't know how much that might cost, but I'm doubting it's free.

Outside transom:


Inside after removal of ply and a bit of cleanup:


Worst spot of corrosion on interior:


Five or six spots of corrosion/pitting like this on interior. Holes are screw holes, not pits.

 

[Skiffing]

Here's my take on corrosion:

https://www.tinboats.net/forum/viewtopic.php?f=21&t=36735&start=15#p383654

 

[chavycha]

The boat is going to be getting a thorough bath soon, and then will have plenty of time to dry out before I seal anything up. There are enough screw holes in the inner skin that I can probably get a pretty decent amount of clean water back between the two skins.

Much admiration for your wiring skills. For what it's worth, this boat isn't going to have any electronics permanently mounted. The motor will be a manual start / tilt and the fishfinder/GPS/battery will be self-contained and removable.

 

[chavycha]

Any thoughts on a rainy Sunday?

 

[huntinfool]

I'd cut the old skin out and install a new transom.
If you don't think you can cut out the old skin, then I'd cut and fit a transom and just before installing it, I'd inject 5200 in between the layers and "sandwich" it between. Then with the 5200 in between, I'd install the transom and clamp it tight.
Make sure you clean the skin as best as you can.

 

[chavycha]

Great idea. I hadn't considered just cutting out the interior skin. The edges of it are fine, and I'd be reluctant to cut near the corners as they are structural.

So I could cut out the corroded center, check what's going on on the back side of the new .125 plate skin, and then put a good ply/glass transom on. Nice. I'm going to see if I can find someone locally who knows this stuff better than I do to take a look in person.

 

[DaleH]

I'd cut the old skin out and install a new transom.
If you don't think you can cut out the old skin, then I'd cut and fit a transom and just before installing it, I'd inject 5200 in between the layers and "sandwich" it between. Then with the 5200 in between, I'd install the transom and clamp it tight.
Make sure you clean the skin as best as you can.

DO NOT use 5200 between sheets of aluminum! Johnny just posted a picture of extensive corrosion from a transducer bedded w/ 5200 against aluminum. I ypthink you'd be better off using steel-flex between the sheets ... as that is what I'm going to do.

As I'm in the 'same boat' ... no pun intended ... replacing a transom. FWIW I boat in saltwater, so I'm going with a new poured ceramic composite transom from Carbon-Core, see their transom compound at www.carbon-core.com.

 

[chavycha]

Okay, so, tentative plan...

Cut out most of interior skin, leaving about a 2" perimeter. Evaluate exterior skin for corrosion. Clean. Clean again. Seal remaining interior skin with Gluvit. Put together a nice plywood/glass transom and bolt to aluminum transom. Reinstall transom brackets. Voila!

 

[huntinfool]

That should work.

 

[Johnny]

Chevy - what exactly have you done so far ? Any photos ?

I have just one question that I am confused over.
You say there are two pieces of aluminum skin on the transom ?
one added by the P/O and welded to the factory original skin ?

can you stick a screw driver in between them and pry them a part some ?

 

[chavycha]

Johnny,

Haven't cut anything yet, so no photos other than those above. I pressure-washed the interior yesterday to get a better idea of what I was looking at under all the dirt. Boat had been stored outside and had collected all sorts of neat lichen and moss.

Yes, there are two skins. They are not bonded together. In the bolt holes I can pry the two skins apart a little.

 

[Johnny]

wow

okay, this is just purely speculation from what I would do if it were my project.

okay - to stop the hemorrhaging of corrosion - - -
Can you get some kind of sharp object such as a machete or big knife between the skins ????
in my world, I would separate the sheets as much as possible with pop cycle sticks or something
non-metallic. then, masking tape all the holes and fill the space between the two sheets with vinegar.
Ospho or CorrosionX would be better if you have it. Maybe drill a couple of 1/4" holes along the bottom
to allow good circulation and drainage of the water and cleaning chemicals.
IF you can pry the sheets apart in some spots to do this.
Let sit a few hours or over night. Rinse, repeat a couple of times.
It may be possible that corrosion is the only thing that is bonding the two sheets together in the middle.
Since none of us are there for a hands on look see - we can only go by your descriptions. So accuracy is paramount.
Turn the boat upside down, use some blue or green painters tape
and try to secure a hair dryer so it blows warm air into one end of the two metals
and out the other. You can remove the tape over the holes for this procedure to provide better air flow.
whew - then, with some suggestions from your fellow members here, turn the boat over,
retape all the holes and pour some kind of liquid hardening/bonding agent which will arrest the corrosion
and bond the two pieces together permanently.
Personally, I would use POR-15 bonding paint to pour between the two sheets . . .
but, like I stated at the git-go, that is just how I would address this issue in MY world.

keep us posted !!!!

If you can get a grip on what is going on between the sheets, you will have a
better "educated" idea of how to tackle the issue. Of course #1 would be if you
can remove the offending skin. #2 is amputation of the entire transom.
But, why cut off the whole foot just to treat a sprain ankle ??? LOL
go SLOW, don't do anything extreme that you can't come back and fix later by yourself.
we can ALL give you information from our recliner, but, you are the one standing
at the operating table (alone) ........ Just try to digest it all and pick something that is within
your skill set to start with. Of course, easiest to the most difficult.