Stern Skin Corrosion - How bad does it have to be - to be replaced?

[WNCMapper]

Hello all, I'm pretty new to the forum, and boating in general.

I've seen DaleH's thread on his rebuild, don't think mine is as bad, but here's my project:

I got this 1994 Lowe (Big Jon) 14X48 stripped down to bare bones. I've got a welder lined up to build an aluminum transom, and do other patch work. Well I removed the orig. plywood transom yesterday and found all this corrosion on the stern of boat - see photos. The worst of corrosion is in the corners, and some of the pitting (small pits at this point, but I haven't chased all the white corrosion) goes nearly through. My gut is telling me I'm gonna need to have the stern skin replaced before installing new transom. Or am I being overly concerned? Will epoxy method work? Boat will be used in smaller rivers a lot - lotsa logs. This is a complete rebuild project. Any experience, estimated cost having stern replaced by welder, etc...?
Thanks for your input!

 

[FuzzyGrub]

I'd talk to your welder on replacing the rear skin. I assume he would be using box tubing and bracing to make up the transom, and that is where the strength will come from. The skin will need to be welded to the framing in different spots. Don't put any coatings on it until your welder looks it over, and decide on a game plan. He will probably walk away from trying to remove epoxy to get a good weld.

I did the transom on my DMI 1648. I found "worm tracks" and had a few pin holes through the back skin and the piece that was on the inside face. I can't tell if it was better or worse than yours. This was caused by the mfg using pressure treated plywood. The pinholes were above the waterline, so cleaned up the aluminum and marine epoxied the pinholes. Then applied coats of Gluivit epoxy. I used a sheet of quality 3/4" exterior plywood to lay-up the 1.5" transom. That also got multiple coats of gluvit. It has been rock solid, but only about 5 years since the repairs.

 

[airshot]

I replaced thevtransom on my jon boat with a piece of exterior plywood and covered it in thompsons waterseal, now it doesn't sit out exposed to the weather, it sits under an awning or turned upside down and that lasted for 15 years, redid it 5 years back even though it wasnt rotted, just wanted to redo the entire boat.. Point here is, how long it lasts will depend on how the boat is stored. Out in the elements, its life will be cut short, taken care of...a looong time. My 1983 Islander has the original factory transom, it is showing some soft spots at the bottom and will need replaced shortly, mabey another year or two at best... Look at its age....no PT plywood, no epoxy coating, no sealing of any sort, but...stored properly all of its life!!
40 years on the original plywood !! Neighbors brand new boat did not make it ten years, because he set it outside in the weather year round, cover was torn up by the second year but he let it go..." boats are made to be outside" was his saying, the transom and stringers were junk in 10 years, yet he blames it on being a cheap crappy boat and recieved no help from the factory with warranty claims...
No matter what we seal, cover, etc you need to take care of it !! Then it will probably outlast the owner !!

 

[WNCMapper]

I'd talk to your welder on replacing the rear skin. I assume he would be using box tubing and bracing to make up the transom, and that is where the strength will come from. The skin will need to be welded to the framing in different spots. Don't put any coatings on it until your welder looks it over, and decide on a game plan. He will probably walk away from trying to remove epoxy to get a good weld.

I did the transom on my DMI 1648. I found "worm tracks" and had a few pin holes through the back skin and the piece that was on the inside face. I can't tell if it was better or worse than yours. This was caused by the mfg using pressure treated plywood. The pinholes were above the waterline, so cleaned up the aluminum and marine epoxied the pinholes. Then applied coats of Gluivit epoxy. I used a sheet of quality 3/4" exterior plywood to lay-up the 1.5" transom. That also got multiple coats of gluvit. It has been rock solid, but only about 5 years since the repairs.

That's great advice! worm tracks and few pin holes describes mine accurately. At this point I have just used a wire wheel, wire brush, scour pads, and simple green 50/50. I feel like if I keep following the corrosion, I'll weaken the skin more - I'll do that this week and have better idea what I'm really dealing with here. Thanks, your advice gives me a viable option!

 

[WNCMapper]

I replaced thevtransom on my jon boat with a piece of exterior plywood and covered it in thompsons waterseal, now it doesn't sit out exposed to the weather, it sits under an awning or turned upside down and that lasted for 15 years, redid it 5 years back even though it wasnt rotted, just wanted to redo the entire boat.. Point here is, how long it lasts will depend on how the boat is stored. Out in the elements, its life will be cut short, taken care of...a looong time. My 1983 Islander has the original factory transom, it is showing some soft spots at the bottom and will need replaced shortly, mabey another year or two at best... Look at its age....no PT plywood, no epoxy coating, no sealing of any sort, but...stored properly all of its life!!
40 years on the original plywood !! Neighbors brand new boat did not make it ten years, because he set it outside in the weather year round, cover was torn up by the second year but he let it go..." boats are made to be outside" was his saying, the transom and stringers were junk in 10 years, yet he blames it on being a cheap crappy boat and recieved no help from the factory with warranty claims...
No matter what we seal, cover, etc you need to take care of it !! Then it will probably outlast the owner !!

Good to hear your observations on storage. I do have a carport for mine, so I'll sleep better at night hearing from your experience!

 

[DaleH]

Well, there is a tin phenomenon called precipitate chloride corrosion and it self-perpetuates. Pick a few spots or holes and see if you see a later of ‘white’ between the inside surface and outside surface. If so, yes .. the panel is a likely candidate for replacement. You can try epoxying smooth and adding wood inside, but the tin can still continue to eat away at itself.

 

[WNCMapper]

Well, there is a tin phenomenon called precipitate chloride corrosion and it self-perpetuates. Pick a few spots or holes and see if you see a later of ‘white’ between the inside surface and outside surface. If so, yes .. the panel is a likely candidate for replacement. You can try epoxying smooth and adding wood inside, but the tin can still continue to eat away at itself.

Thanks for input Dale. I'll start chasing the white corrosion this weekend...

 

[DaleH]

‘Layer’ of white corrosion inside the tin itself, sandwiched in there if you will.

 

[LDUBS]

‘Layer’ of white corrosion inside the tin itself, sandwiched in there if you will.

OK, sometimes it takes me awhile but the lightbulb finally just clicked on. Now I understand why it would be difficult to neutralize.

 

[atw7]

OK, sometimes it takes me awhile but the lightbulb finally just clicked on. Now I understand why it would be difficult to neutralize.

I bot a 14' 1980ish Fisher Marine Waterrover. It was used in salt water and the transom is full of pinholes and corrosion mostly around the bolt holes. I cleaned the transom with cleaning vinegar and used a toothbrush to get into the pitting. Rinsed it with water and let it dry. Then I sprayed it with self etching primer to prevent additional corrosion. At this point, my plan is to bond another piece of aluminum to the inside with Loctite PL Marine and immediately bolt it back together with the new plywood.

 

[WNCMapper]

‘Layer’ of white corrosion inside the tin itself, sandwiched in there if you will.

 

[WNCMapper]

I got a more aggressive grinder and started cleaning out the precipitate chloride. The holes got bigger and bigger, and still white layer "in between". I'm going to have welder replace the whole stern. I'll report back or post the complete the project when I get more organized. I'll be back sooner than later cause this is all new to me, but it's a fun mission of discovery!

 

[Douglasdzaster]

I got a more aggressive grinder and started cleaning out the precipitate chloride. The holes got bigger and bigger, and still white layer "in between". I'm going to have welder replace the whole stern. I'll report back or post the complete the project when I get more organized. I'll be back sooner than later cause this is all new to me, but it's a fun mission of discovery!

I got lucky with the bottom of mine. It had places that looked like the pictures you posted of yours. I did better with Nyalox brushes than a wire wheel. I ended up using a Dremel and magnifying glass to get the last of that nasty stuff. Luckily it wasn’t spreading bad. That’s when I just used polish and kept it covered for 6-7 months and none came back. I stripped off the polish and rolled on truck bed liner and built a new floor.
Maybe I’ll get a few years out of it. Mine is a 1983ish Monark 16/52. With a 1995 I think 40 hp Yamaha. I drug it out of a field for a little cash my wife saved up so I could have a boat. Boy does she regret it.