Transom is corroded

[imjohnnykelley]

Hey there new friends. I am new to the forum, and excited to learn. I just picked up a 17' polar that I am going to convert into a flats fishing boat for inshore salt water fishing down here in the Tampa area. When I got it, it had two sheets of plywood sandwiched on the inside and outside of the transom. Obviously I want to get that taken care of the right way, so today I ripped into it. Well the aluminum under it was not pretty. A ton of corrosion, and holes. So what do I do? Do I get a new rear end welded on? Do I walk away from the boat (definitely don't want to do that). Or is there a simpler way? What would you do?

Looking forward to reading the responses, and thanks for the help!

 

[DaleH]

Ouch ... that boat needs new transom skin or skins (if an inside one too). See my signature post for how I put a new riveted transom in.

 

[imjohnnykelley]

Ouch ... thst goat needs new transom skin or skins (if an inside one too). See my signature post for how I put a new riveted transom in.

Definitely need one. Would riveting in a new one like yours be better or would getting a sheet welded in be better? I have a friend that welds aluminum and will do it for free if I want.

 

[DaleH]

Well, I would get ALL of that corroded piece out, don’t leave any of it in there ...

 

[nccatfisher]

It would be easier and structurally more sound to just replace the whole transom.

 

[imjohnnykelley]

Well, I would get ALL of that corroded piece out, don’t leave any of it in there ...

Well I have done a ton of work on fiberglass boats, but this is my first step into aluminum. Is there a place to learn about types of rivets and what kind to use? It doesn't scare me to replace it all, just want to do it right and need to know how to do it.

 

[KMixson]

After replacing the transom it would be best to not sandwich it between plywood. You don't want pressure treated wood in contact with the aluminum. Some types of pressure treated woods will cause this. Another reason not to sandwich the transom is so you can see the condition of the transom visually without taking it apart at least on one side.

 

[imjohnnykelley]

I know that replacing the aluminum would probably be the best solution, but had another thought that I know would last a long time and wanted to see what you guys thought. I am not married to any of these things yet, just looking at different ways to do it and seeing what would give me the best options that fit in my skill set right now. So here is my idea:

I could sandwich it again, but this time I would epoxy and fiberglass the wood on both the inside and outside. I would 5200 around the edge of both pieces before putting them up, and then put them up wet with epoxy so it would adhere. It would be very strong and as long as I do my job on the fiberglass it would be completely waterproof. Would be very strong and rigid as well.

Like I said, I am not married to the idea, but it is something I know how to do and I think it could very well be a fix that lasted a long while. Thoughts?

 

[imjohnnykelley]

This morning when it got light out I went out to investigate. The rear of the boat is welded on to begin with. Not riveted. So my options are either cut off the back and weld in a new one, or do something closer to what I said in the last post.

 

[Johnny]

Johnny - agreed; that really does look bad !!

have you ever used POR-15 rust encapsulator ?
there is a way of using POR-15 to keep what you have, beef it up a little,
and still get a few more years out of it without drastic surgical measures.






.

 

[imjohnnykelley]

Johnny - agreed; that really does look bad !!

have you ever used POR-15 rust encapsulator ?
there is a way of using POR-15 to keep what you have, beef it up a little,
and still get a few more years out of it without drastic surgical measures.
.

Never used it. Will it work at stopping corrosion on aluminum? I would rather avoid major surgery and try and make it work for a while. Was thinking today I could sand down that transom aluminum on the inside and out till I get rid of everything nasty. I could then paint it with at stuff. Then I could take a sheet of aluminum the same size and alumiweld it inside the boat all the way around. Then I could epoxy fair the whole outside rear and sand it smooth before priming and painting. Then add a thicker red wood transom instead of the nasty unsealed plywood that was in there.

You think that could make it work for a few years?

 

[CedarRiverScooter]

Good plan except for painting before welding. Fumes really bad for you.

As long as you are welding, why not just add sq tubing braces & eliminate wood altogether?

 

[Johnny]

the object of the game is to remove all oxidation from the metal.
bottom line is to prepare the metal to prevent ANY future exposure to air and moisture.
first smooth it down mechanically with sanders, grinders, media blasting, etc.
then with chemicals such as diluted muriatic acid in a spray bottle. (baking soda rinse to neutralize any acids used). RINSE WELL.
this is where your expertise with fiberglass comes into play.
POR-15 is a very tenacious moisture curing one part urethane that once it grabs onto something, it is impossible to remove.
the surface it is applied to will be forever impermeable to air and moisture.

the basic steps would be as above: mechanical and chemical stripping and cleaning.
clean and etch with OSPHO. apply masking tape to the holes from the outside of the transom.
paint inside desired area with POR-15 - when it is tacky - apply a layer of fiberglass - roll out bubbles.
apply a top coat of POR-15 over the glass just as in the typical polyester resin/glass repairs.
let that cure for 24 hours and repeat. repeat again if desired.
for the outside of the transom - do the same thing one time...... sand, fill defects with Bondo, prime and paint.
fabricate new transom panel, (either wood or aluminum tubing) seal and paint as required.
POR-15 is not UV tolerable and must be painted. the same with polyester resin and epoxy.

a bit time consuming but will add years to the life of your boat. plus you retain the original shape and integrity of the hull.
if you go sandwiching metals together, eventually air and water will find its way in and introduce corrosion again.

if this is something you would be interested in, call the POR-15 tech people and they can walk you through
the process that applies to your situation and discuss your options. https://www.por15.com/

if that was my boat, that is what I would do (and have done).
if the corrosion damage was too much for that, I would go with Dale's option of a complete cut out and rivet in a new patch.

 

[imjohnnykelley]

the object of the game is to remove all oxidation from the metal.
bottom line is to prepare the metal to prevent ANY future exposure to air and moisture.
first smooth it down mechanically with sanders, grinders, media blasting, etc.
then with chemicals such as diluted muriatic acid in a spray bottle.
this is where your expertise with fiberglass comes into play.
POR-15 is a very tenacious moisture curing one part urethane that once it grabs onto something, it is impossible to remove.
the surface it is applied to will be forever impermeable to air and moisture.

the basic steps would be as above: mechanical and chemical stripping and cleaning.
clean and etch with OSPHO. apply masking tape to the holes from the outside of the transom.
paint inside desired area with POR-15 - when it is tacky - apply a layer of fiberglass - roll out bubbles.
apply a top coat of POR-15 over the glass just as in the typical polyester resin/glass repairs.
let that cure for 24 hours and repeat. repeat again if desired.
for the outside of the transom - do the same thing one time...... sand, fill defects with Bondo, prime and paint.
fabricate new transom panel, (either wood or aluminum tubing) seal and paint as required.
POR-15 is not UV tolerable and must be painted. the same with polyester resin and epoxy.

a bit time consuming but will add years to the life of your boat. plus you retain the original shape and integrity of the hull.
if you go sandwiching metals together, eventually air and water will find its way in and introduce corrosion again.

if this is something you would be interested in, call the POR-15 tech people and they can walk you through
the process that applies to your situation and discuss your options. https://www.por15.com/

if that was my boat, that is what I would do (and have done).
if the corrosion damage was too much for that, I would go with Dale's option of a complete cut out and rivet in a new patch.

Dang.....that is exactly what I am gonna do. All that makes sense to me. I just didn't know the process with aluminum. Thanks so much. So I would use the POR-15 as the wet out instead of resin. That is a great idea man. Instead of bondo I will use Total Fair instead though. It is built for this (it is an epoxy based resin fairing compound). It is expensive, but I have a bunch of it already. It is made to use on boats below the waterline. https://www.totalboat.com/product/totalfair/. Other than that, I will do exactly what you said. Love it. Thanks for the plan!

 

[Johnny]

you are very welcome !!

polyester resin and epoxy do not play well with aluminum.
you will soon experience separation issues which invites corrosion (again).
try to find a source for a good quality Zinc Chromate Primer for other areas of your construction.

yes - the POR-15 is the wet-out agent and is EXTREMELY tenacious in its adhesion properties.
I have worked with it for over 20 years or so and their product line changes periodically and I am not
up to date on what is available today for your issues. just call the tech desk and get it straight from the horses mouth.
when you get all the materials on hand, give me a shout back and I can go over the project with you
and shorten your learning curve. (and there IS a learning curve).

good luck !!

oh - here is how I made a transom panel out of aluminum tubing:





you can use whatever thickness of materials to achieve the 1-1/2" thickness required for the panel.
This is just what I had on hand. The pieces are assembled with construction adhesive and pop-riveted
together. whatever adhesive you use, it MUST BE aluminum friendly. 3M-5200 and some some adhesives
state right on the label - not for use on bare aluminum - so take that into consideration.
also, take a moment and see where the motor mount bolts will go and try to position the tubes so the
hole is drilled through the cavity of the tubing - not through the wall of the tubing (guess how I know this little tidbit).
after the transom skin is rebuilt, you will not need a wood panel on the outside that covers the whole hull.
just one piece big enough for the motor mount.




.

 

[Prowelder]

Here is one I did very similar to yours

Sent from my SM-G955U using Tapatalk

 

[Hanr3]

Couple of comments.
I have used POR15 on a gas tank. We bought a used S10 Blazer for my son and the gas tank had rust holes about half way up the tank. We dropped the tank, cleaned it up best we could, then followed the directions on the POR15 stuff. Worked like a charm and took care of the rust issues. Son drove that truck for another 4 years until we sold it. Never had an issue with the gas tank, or stuff in the fuel.

Wood, IF you are replacing the wood I highly recommend White Oak. It will cost more, however it will last your lifetime, even submerged. Plus it is extremely strong and you wont have any issues with motor weight or transom integrity.

 

[imjohnnykelley]

Today I got the interior wood off the transom, so now I only have the aluminum left on the back. Well I have what is left of the aluminum. There are probably 30+ holes of different sizes and a giant hole about 1.5 ft. And I haven't even started sanding it down. I am not sure that it is salvageable with the POR-15 and glass. Do you think it will handle a gap like that? Or am I fighting a losing battle and need to come to grips that it is time to weld in a new rear end? I'll post a pic tomorrow to show you what it looks like right now.

 

[DaleH]

Have you ever used POR-15 rust encapsulator ?

Never used it. Will it work at stopping corrosion on aluminum?

Here's the deal ... IF that aluminum corroded because the wood was wet with saltwater and IF you see a white layer of chloride (salt precipitate) in the alloy of the transom, then your transom has the condition known as precipitate chloride corrosion and the ONLY cure is a complete removal. It is like a cancer! Once in there, it actually feeds on itself as it moves through the tin.

This is what I warned you against.

Clean up an area well and get a magnifying glass and a good light. If you find a 'pin hole' ... how 'big' do you need to drill out that pin hole before all traces of a chloride layer are removed? When I checked my transom, I started with some < 1/8" holes that ended up being 3/8" in diameter and yet under review by a good magnifying glass, I could see a white corrosion layer inside or in the middle of the tin panel. If you have that, IMHO it requires total removal of the affected structure.

 

[eshaw]

That piece of aluminum is unfit for attaching anything to, it just won't provide a good base for any repair. I think the only solution would be to remove and replace it. Not trying to be critical of your boat but is this the only place you've noticed problems?