’97 Starcraft Corroded Transom Repair using Pourable Ceramic

[DaleH]

This post linked to below shows a pin-holed transom of someone else’s skiff .. and alas, mine has a similar condition . But in my case, I bought the rig at the right price , full well knowing that I’d have some expen$e and have to do some work on her - but I was ready for it! No surprises ... :wink:

The previous owner had also affixed a piece of aluminum skin to the hull, but the person who did it for them didn’t seal it or the previous corrosion holes well. Adding to that they used plain steel fasteners on a boat used in saltwater, thus it was an ugly repair, but that again actually helped me immensely with the purchase. And of course, a few of these self-tapping screws were below waterline … oh what were they ever thinking …. ?

Link = https://forum.tinboats.net/viewtopic.php?f=3&t=37415

BACKGROUND
From discussions here, other post on-line and with Andy at Starcraft customer support, I’ve come to the conclusion that the damage was crevice corrosion caused by saltwater that got in-between the unsealed wood and rear skin. Some form of reaction took place, as the blisters are full of salt and came out from the inside. At least it is fixable.

RESOLUTION
I have done many a transom repair; on wood, tin and frp boats and for this one, I believe I’m going with CarbonCore's pourable ceramic compound, as made by the NidaCore Company. I looked at Arjay, Seacast, and NidaBond products and it looks like the CarbonCore and Arjay products are the same product as made by NidaCore. The rating on it this pourable compound has 7X better compression strength than plywood (attached some PDF info on it & pricing for two 5-gallon pails). And they say it is a better material and less costly than the Seacast product. I called and emailed Seacast too, but have yet to receive a reply. Oh well, their loss.

I'll finish off the outside of the transom skin with thin coats of the epoxy products well used here, e.g., PRO-15 or Steel-Flex. I haven't yet determined whether or not I will add a layer or 2 of mat with the epoxy 'finish'. Any input on this :?: ?

RATIONALE
Yeah, yeah, yeah … I know all about how much cheaper a wood/epoxy or wood/spar varnish transom can be and I agree with you … but the 2 main items of my concern are (1) Time and (2) Teardown of the entire stern.

I have already walked the hull over - inside and out - and the only place I have this corrosion is limited to just the outside of this stern piece. The rest of the hull is minty mint! And the floor? No rot anywhere. And the foam? Sound, I cannot detect any moisture anywhere.

This boat was always covered whilst on the mooring or when stored at home and I even used a 24” lighted inspection camera into the deep bowels of the hull and cannot find even ONE thing that would justify re-riveting her and tearing the entire stern apart ... and then having to put her back together again. For example, this hull shows absolutely zero corrosion on the inside-piece where the wood is also sandwiched, as the entire wood piece is encapsulated by tin covering.

So … stay tuned for more pictures as I ‘git her done’!

Some pictures are attached for what I’m already into. LOL! And I just LOVE that 16-degree deadrise … as you don’t see that too often on 16’ tin boats. She is a 1997 FishMaster 160 SC model, powered by the ‘Classic 50’ Mercury 4-cylinder 40hp 2-stroke OB, which allegedly puts out 45+hp.

 

[DaleH]

Here's today's progress ... as the splashwell was integral to a U-shaped section that also formed the port & starboard cavities that were full of dry foam.

But of course there were a good dozen SS bolts per side and between them reacting with the aluminum (galvanic corrosion) on this boat used in saltwater ... I also see evidence of crevice corrosion, where SS screws installed in blind or closed quarters had wicked corrosion, but those in exposed areas were sound.

 

[DaleH]

Here's the splashwell section ...

As a bonus ... can you believe I only had to drill out 3 rivets per side of the boat, to get that section out? (Less all the SS bolt removals ... )

 

[DaleH]

Clearly I'm going to have to prep, then coat and seal that inside skin really well where the splashwell 'skin' lies on top of it. I may even consider wetting out the interfaces with PRO-15 or Steel-Flex before joining together. Then further seal all edges with 3M 5200.

Look at the salt deposits :shock: in between these skins!

 

[Johnny]

awesome project !! I love a good challenge like this. (time and money permitted).
I love working with aluminum and fiberglass components.
question: is this for your personal use or you gonna get it ready for resale ?

When I worked at a boat yard in Key West, FL back in the 70s, the owner of the
yard told us "grunts" to just sand it off, paint it over, slap on some lipstick and get it SOLD.
Many looked just like your project at hand. Back then, we used a LOT of zinc chromate.
We even painted over salt encrusted metals that looked like mashed corn flakes.
And now, you are catching all the years of neglect and improper ways of doing things.

As for the metal - wow - there are a few options there.
#1 would be of course sandblasting, if that is even possible, to get to bare metal.
#2 is the POR-15 on top of CLEAN metal and/or fiberglass/epoxy.
#3 are you going to replace the outside skin that the P/O made ?
I personally don't like the idea of two metals sandwiched together. Just for the reason you see.
If you do, (in MY world), I would put a layer of fiberglass cloth and resin between the two
to prevent future galvanic issues. (jus my dos centavos there). I think the poured transom would
give you enough strength that you would not even need the outside skin.
But, I am not familiar with the pourable transom mix -
You mentioned the foam was dry - - - is it sound ? or turns to dust when you mess with it.

I will give the POR-15 another plug. If sandblasting is not possible, (in my world), I would arrest
the corrosion by whatever means necessary: vinegar, OSPHO, acid, etc. to get it arrested.
then, a few layers of brushed on POR-15 (even tho it is quite expensive). Then, pour the transom mix.

Looking forward to the Step-by-Steps !!!!

 

[Megabyte]

Now that is a project. :wink:

 

[DaleH]

Tonight's tasks ... clean and prep the aluminum to get ready for the pour ...

 

[DaleH]

Awesome project !! I love a good challenge like this.

Thanks for the kind words and input! I love projects too, but my time for this one is somewhat limited, which forces my use of the pourable mix … only due to the way I would otherwise do it.

As typically when using any through bolts on a wood-cored transom (even on frp boats) and especially on a boat that will be used in saltwaters, I would drill through a 3/8+” hole for use with 1/4” bolts, then wet-out the core with thinned epoxy and once that kicked, I’d back-fill it with a syringe using a thickened formulation mix. Then I tap drill through the epoxy plug to leave a permanent and waterproof epoxy core. It’s fool proof … but takes time for the multiple steps per hole and Starcraft has used 40 SS bolts to secure together the splashwell and stern compartment boxes to the transom skins – zowie! That would be a lot of holes to fill …

Question: is this for your personal use or you gonna get it ready for resale?

This will be for my own use, as I’m down-sizing from an offshore toona boat into something much smaller. I just want to get back into flyfishing local estuaries for striped bass and bluefish. I’ll now do my offshore fishing, as crew on the best type of boat there is … OPBs! (Where OPB = Other Person’s Boats!)

I personally don't like the idea of two metals sandwiched together. Just for the reason you see.

Yes, agree 110% with you there! I will clean and prep the material, then put POR or Steel-Flex with or without a layer of mat in-between any such interface (still looking into it). All edges to be sealed with thin bead of 5200, then top-coated with either epoxy-matrix ‘paint’, prior to spraying the transom a new uniform color all over.

I think the poured transom would give you enough strength that you would not even need the outside skin.

I think so too, but to be sure I sent pictures to Carbon-Core’s technical staff and their ‘tech’ guy is reviewing them now. Whereas the strength rating on the poured composite material is 7X that of plywood, while retaining some flexibility, I’m inclined (right now) not to replace the skin, given that by proper preparation, their composite will mechanically bond to the aluminum skin forming a laminated structure. If it cured on its own and had no properties to ‘bond’ to the aluminum skin (inside or out), then yes – I’d be adding a skin via the sandwich method you noted with frp mat in-between.

You mentioned the foam was dry – is it sound? Or turns to dust when you mess with it?

I got lucky – it is dry and sound and doesn’t appear to have suffered a bit from the years enclosed in those transom side compartments. All foam on the boat is integral and dry!

Oh, that old piece weighed about 50-pounds and was still oozing a white watery mix of water, salt, and wood-breaking-down ... and that hull hasn't seen the water since Fall 2013.

 

[Johnny]

opcorn: this is gonna be one awesome tutorial !! thanks for sharing :beer:





my brother bought a 20' I/O Sea Ray couple of years ago, the outdrive unit burned up
some bearings and I helped him remove it. While the unit was out, we could not help
but notice the transom wood was rotten and wet.
The boat sat in his driveway for a year before he got tired of looking at it and sold it for
pennies on the dollar he bought it with. (he got it a really good deal on it - now we know why).
JUST BECAUSE neither one of us wanted to mess with the enormous task of replacing
that transom. (on a SeaRay, that is a BIG deal) At that time, neither one of us
had even heard of the pourable ceramic product.
Soooooo am really paying attention to your post. As well as doing other searches on
the net, youtube, etc. You never know when you might find a good bargain like yours . . . .
I know my way around fiberglass and aluminum boats quite well - but - this product is new to me.
As with any hard to get to fiberglass boat transom, I think now I would not hesitate to cut the
wood transom from the OUTSIDE. Remove all the old wood by whatever means necessary,
seal all the holes, make a cofferdam around what big holes that need to be there, and pour the resin
in steps to ensure no blowout occurs, then, glass and matt the skin back the way it was.

Thanks again for sharing.

 

[DaleH]

Dang it ... the rear skin had a tad more corrosion in it than I am comfortable with ... so I will replace it.

So now before the 'pour', I'll be de-riveting the stern piece and fabbing a replacement from a sheet of 5052-34 alloy I just picked up, 0.090", which ran me ~$160.

It turns out that the salt (chloride) corrosion travels laterally THROUGH aluminum,along the grain boundaries, which means you can't ensure you got it all out and as Barefoot Johnny states ... Ol' Lazarus (corrosion) will rear it's ugly head soon enough again. Like a cancer, I'll cut it out completely and replace the entire panel.

I'll try to get a good close-up picture of the corrosion I found where saltwater was allowed to weep and wick in between the wood and rear skin ... where it just continually ate away at the metal, exacerbated in areas where stainless steel (SS) bolts were put through too.

Ah well, that certainly pushes the 'pour' date ... and launch date ...back a few weekends.

 

[DaleH]

my brother bought a 20' I/O Sea Ray couple of years ago, the outdrive unit burned up some bearings and I helped him remove it. While the unit was out, we could not help
but notice the transom wood was rotten and wet. The boat sat in his driveway for a year before he got tired of looking at it and sold it for pennies on the dollar he bought it with. (he got it a really good deal on it - now we know why). JUST BECAUSE neither one of us wanted to mess with the enormous task of replacing that transom. (on a SeaRay, that is a BIG deal) At that time, neither one of us
had even heard of the pourable ceramic product.

. .. I know my way around fiberglass and aluminum boats quite well - but - this product is new to me ... I think now I would not hesitate to cut the wood transom from the OUTSIDE. Remove all the old wood by whatever means necessary, seal all the holes, make a cofferdam around what big holes that need to be there, and pour the resin in steps to ensure no blowout occurs, then, glass and matt the skin back the way it was.

FYI, here's a GREAT tutorial showing the pourable ceramic transom process on a plastic boat, just as you described ... cut into from the outside.

https://www.classicmako.com/forum/topic.asp?TOPIC_ID=44076

 

[Johnny]

Thanks Dale - great read, great project, awesome tutorial !!
I am far more "at home" in old wooden and fiberglass (FRP) boats than aluminum.
I guess that is because I have much more experience in them than tin.
Ironically, I have already been looking for an old 18-20' Mako hull for a project.
My wife will be gone for July-Aug-Sept and that will give me some "alone time" to at
least get it gutted and cleaned up before she gets back LOL LOL . It will take about a year to do it right.

As for your project at hand, I think you made the right decision of removing any suspect metal.
The Lazarus Effect is a terrible thing. Cancer, no matter if it is in a human body or wood or metal,
can seem benign, in remission, or "gone". Only to reappear and kill its host. That is life.
It could take a few months to several years, but the end result is the same.
Corrosion is a maintenance controlled issue. But, only if you can get to it. If you weld it up
or rivet it up or cover it up with adhesives, it can not be maintained or controlled. Then, when you DO
have an issue that resembles Swiss Cheese, it is way too late.
Good call on catching the bad metal.

Looking forward to "The Pour"

Johnny

 

[DaleH]

Looking forward to "The Pour"

Well, before I can pour I need to completely REPLACE the transom rear skin. I've seen a lot of posts here of people adding wood, but I have yet to see or find where someone has replaced the OEM rear panel. This was my method to remove it and DE-rivet the boat ...

1) Quick wire brush so I can see each brazier rivet head easily, whilst sitting down on the work stool - at best, or whilst lying under the boat -at worst.

2) Place dot on center of each rivet head w/ black Sharpie marker.

3) Using a prick punch (60-degree included angle or less) pick up the dot and strike with ballpeen hammer.

4) Switch to pin punch (90-degree included angle) and widen/deepen the spot to drill. Many may not know, but I learned this at GE's apprentice machinist school, that by using the 2 punches in tandem, you get a more accurate dimple to start the drill and it's even possible to tweak the center punch off to one side or the other if you had goofed a tad on the prick punch.

5) Drill in ~1/16" w/ 3/32" cobalt drill. Do about 6 or rivets, maybe more.

6) Drill in w/ 3/32" cobalt drill, I found that 3 quick medium power hits kept the torque on the bit and ~70% of the brazier heads sheared right off at the top surface. I didn't need cobalt for aluminum, but they sure stay sharper!

7) Punch out or through and replace every 3-4" with a Cleco temporary fastener.

Lookie there ... she looks like a porcupine!

 

[DaleH]

For those who have never seen them, Clecos are temporary fasteners for when working with sheet metals. They're spring loaded, but I used enough on the skin around where I working 'from', so it was at least supported and held together as I progressed down the sides and on to the keel. They worked slick!

This kit was only $25 (3/16" size) and it gave me 30 of them with the pliers. And now I have MORE COOL TOOLS to add to the collection!

https://www.irvansmith.com/scart/316-cleco-kit-p-198.html

Clearly this a place where a picture is worth a 1,000 words ... thus I present the following pictures ...

 

[DaleH]

And HERE is where I left off ...

 

[Johnny]

eeeewwwwwwwww


Dale, I was just thinking of you today . . . wondering what you have accomplished so far.
looks AWESOME !! LOL from the "metalsmith's" point of view LOL nice challenge, to say the least.

Do you remember saying . . . But in my case, I bought the rig at the right price , full well knowing that I’d have some expen$e and have to do some work on her - but I was ready for it! No surprises.

are you still within your budget ? I know the "time factor" flew right out the window on this one.
I am very familiar with the Cleco fasteners .... once you do some metal work, nothing else will do.
I like those little clamps too.

good luck !!!!

 

[DaleH]

The next challenge ...

Replicating the shape and rounded corners of the old transom piece without buckling it or tearing it from the sheet panel of 5052-H34 I bought. Looks like I'll be annealing the corners carefully. At least 5052 takes a bend easily.

That heavy scored line you can see right before the rolled corner is where the transom rear skin met the topsides or hull bottom.

--------------------------------------------------------------------------------------------------------------------------------------------

5052 Aluminum Alloy
This is the highest strength alloy of the more common non heat-treatable grades. Fatigue strength is higher than most aluminum alloys. In addition this grade has particularly good resistance to marine atmosphere and salt water corrosion. It has excellent workability. It may be drawn or formed into intricate shapes and its slightly greater strength in the annealed condition minimizes tearing that occurs in 1100 and 3003.

Applications: Used in a wide variety of applications from aircraft components to home appliances, marine and transportation industry parts, heavy duty cooking utensils and equipment for bulk processing of food.

 

[DaleH]

Update:

First shown is the piece I need to copy exactly. Then see the PDF article on 'hammer forming' aluminum. That's what I need to do to form the two corners in my transom piece, plus the center V area (16-degree deadrise).

I will anneal the aluminum first and bought a 650-degree TempleStik so I can't mess up (the annealing temp of 5052 alloy). I'll try my hand at annealing the bend area using MAPP gas. Then I will use a big flat, heavy rubber mallet to form the stern piece. I am using the old stern piece of 1-1/2" plywood as the form, where I cut the 3/8" radius on the edge with a router. I'll place a piece of hardwood across the top immediately behind the edge to be hammer-formed, so that the edge area absorbs the hammer blows.

That PDF article on hammer-forming makes it look pretty easy. And they formed that cap using 1/8" (0.125") thick :shock: aluminum. At least I'm only using 0.090" thick piece of 5052-H32 aluminum, lol.

FWIW I took it to a not-so-local hot rod guru who is the alleged zen master with forming sheet metal ... and he wasn't interested in the job . But at least he told me to research aluminum hammer-forming on-line and advised how to do it myself. And 'at best', he said, that even if I created a small crack or such 'at worst' ... just get that area welded.

Wish me luck ... I will need it!

 

[DaleH]

Hammer Forming a NEW Transom Piece:

If you don't know what 'hammer forming' is, it is a method of forming metal alloys by annealing the piece of metal and then using a form and a large, heavy flat-faced hammer or mallet of wood, nylon or rubber (but NOT metal) to bend and coax the metal to form a new shape. In my previous post just above this one, I have a PDF showing someone making a round dome out of 1/8" thick aluminum. They made it look easy! With a properly annealed piece of metal, the metal will stretch or shrink, depending on whether or not you are doing an inside or outside formed corner.

You can see my layout lines, as I just drew a central line (square the the transom), then others lines parallel to it and 2" out on each side, then measured just to the 'top' of the radius of the bend.

Annealing:
I used 5052-H32 alloy, the same as Starcraft used, and it anneals at 650-degrees F while it's melting point is > 1100. I bought one of those special TempilStiks brand sticks that melts at the temperature you want. I use to use low-temp ones to troubleshoot OB thermostats, so I was very familiar with their use.

For heat I bought a MAPP gas gun and nozzle, as most cheap propane nozzles shouldn't be used with MAPP gas. This nozzle gave a great flame tip and the alloy heated up quickly - just DO NOT keep flame in one spot. I found it best to start from an end and work a 3-4" area. Once the tempstik melted on that area I moved on. On the corners, one must heat the ENTIRE surface or it won't fully shrink or stretch, but will ripple on you.

This was my 1st time doing this and I found the aluminum to be pretty forgiving. Aluminum will naturally harden in air and it also work hardens, so when forming that 1st corner, once it started to be more difficult than it should have been ... I stopped and annealed it again.

I think the pictures tell the story pretty well! I didn't form the 'V' at the center of the hull and up to the other side yet, but I was able to test fit the starboard corner into the existing stern-less hull and I'm pretty pleased!

 

[Johnny]

wow - next month you will have an old forge and stake bed table in your back yard

look up " Planishing Hammer " when you get a chance. . . . . that might be your next calling.
https://www.youtube.com/watch?v=sK0oGJEf1Hk

But, from a true Craftsman's point of view, you can not replace the hammer and anvil approach.

Thanks for sharing !