Dropping and Re-Hanging Cast Iron Stub and Swing Keel

[Charles Brennan]

Spot, THAT is not that rusty a keel!
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THIS is a rusty keel!!   
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Check the blue paint towards the bottom, that was the original paint trapped under layers of rust! 

It took several weekends of chipping hunks of rust with a welding hammer and grinding with an angle grinder to get it just to look like this:
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And that was only on the one side!!     
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Let me preface this by saying I'm a BIG Fan of Coal Tar Epoxy.  It was recommended to me by my Mentor, Charlie Jones in 1999 and he was right then (even when I made some mistakes in the repair) and he was right in 2014.

However, your keel and stub is not NEARLY so grundgy as mine was.
If my keel had looked like:
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Think I would have coated the rusty area with some Naval Jelly, painted it and called it good; but that's just me.

A lot of times when you get advice on this board, it usually slants to the conservative, over-do it kind of suggestions, because NOBODY wants to be the Author Of Bad Advice. 
So, somewhere between a total Coal Tar Epoxy refurbishment and a lame paint job, is probably where you should aim.

If it was me in your shoes, I would use the purple wheel, and get a quart of Ospho.
https://www.ospho.com/directions.htm
I'd hit it with one coat, maybe two if you see any rust, then finish it with your Rust Oleum finish.

The key to a good application is a uniform whitish-grey (the Ospho people claim almost black; they lie, look at the pics) color from the Iron Phosphate chemical conversion.  This is like an M&M, a thin candy coating that keeps oxygen off the metal and the finish paint protects the coating.  Do it right and it looks like this:
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And whereas I was fighting a 400 lb behemoth, you're able to deal with more manageable 200 lb hunks of metal.

If I had to rate (IMHO) the various things out there to prioritize your project, my choices would be, in order:
1) Oshpho (coats as required) and a coupla top coats.
2) Rust Oleum Rust reformer and a coupla top coats.
3) Rust Oleum Rusty metal primer and a coupla top coats.
4) Naval Jelly and a coupla top coats.
5) Rust Oleum clean metal primer and a coupla top coats.  (Although I wouldn't hold out much hope on it lasting any length of time.)

Hope this helps,
Charles Brennan

[Spot]

Thanks CB, I really appreciate the Ospho / Rustoleum decision matrix and photographic comparisons to your project. I take it that the top shelf option up would be coal tar epoxy after Ospho and the bbttom end option would be to do nothing or perhaps even worse, hit it with a coat of something just to make it 'short term pretty' without surface prep.

In the meantime, I ran the blade and stub through CAD and calcutated that it is near 256# / 116kg. If it were to be foiled within its current 'envelope' I'd loose about 23# / 10kg. I might check with a foundry and see what it would take to cast a new one as a curiosity, probably will be 'too rich for my blood' but since metal casting is another hobby of mine it seems sort of fun to ask...

Everyeon-
I appreciate all the advice given here and understand the risk and reward are all mine.

Wayne,
LOL, I think you posted the same link as me for the purple wheels
They seem to be the ticket for this project, I can report back after I get the right spindle nut and really run one through its paces.

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[Charles Brennan]

Spot, Those rankings are not arbitrary, but come from hard-won sweat equity.  My boat came with a Trail-Rite trailer from California, that was painted steel.  I am sure it does a bang-up job in fresh water high-altitude lakes in California where there is already a dearth of oxygen, but down here in sea-level salt-water south Florida, I had to baby it for the 5 years it took to fall apart completely, sinking my boat in the driveway. 

Year 1: Trailer was fine.
Year 2: Wirebrush and Rust Oleum metal primer and two finish coats.
(They weren't calling it "Rusty metal primer" back then, just metal primer.  Naval Jelly worked, but required too much for the size of the trailer, to be economically feasible.)
Year 3: Grinding, Rust Oleum Rust Reformer and two finish coats.
Year 4: Chipping, grinding, Ospho, three finish coats.
Year 5: Nothing but rust holding hands and the rust had an argument and broke up, leaving various piles of rust in my driveway, with a boat sitting on the bunks.

Got a galvanized trailer in 1983 and never looked back.  (Still have it, BTW.)
Transferring the boat from the rusted out hulk and onto a brand new trailer in a driveway involved what my wife refers to as: "Scary Engineering" and drew quite a crowd of neighbors; all of whom were apparently disappointed that there were no significant injuries, or destruction involved.

Dunno as I would worry all that much about the NACA 15 foil.  I obtained a NACA 15 file somewhere on line, keyed in my keel dimensions downloaded the subsequent .pdf file and printed it out on two sheets of A4 and taped them together onto some cardboard, like so:
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Cut it out . . . .
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. . . . .  and when I put it next to the keel so see how much fairing I would need . . . .
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I found (to my astonishment!)  that the keel was already cast that way.
I was going to add some hideously expensive epoxy fairing to build up a NACA 15 foil and found I didn't need to.

Not to be overly critical of your boat's keel design, but it seems to me, the disruption in flow from your stub keel would tend to negate any slight advantages gained by fairing the keel to a NACA 15 foil shape.  More Learned Marine Architect types might chime in with dissent, (and the Math to back it up!)    but that is just my gut feeling.

Just one guy's opinion,
Charles Brennan   

[Noemi - Ensenada 20]

"Scary Engineering" - heh.

[Spot]

I got about 1/2 of the keel stub sanded and the part that mates to the boat.
It took maybe 1/2 hour and one purple disk?
All was going well until I knocked it off the dolly putting it away and it landed on the power cord for the oscillating multi-tool and cut it clean in half. Had to piece it back together (crimps and electrical tape) before I could call it a night. I guess that is a quick lesson in keeping the work area clear, so glad it was not the live cord to the angle grinder...
It smelled like resin while sanding, just like the rudder repair smelled like resin. Wondering if that was factory or previous owner's material of choice?

[Noemi - Ensenada 20]

I know I coated my cast iron keel with epoxy resin before I faired and painted it. 

You ARE wearing a respirator, right???

[Spot]

I know I coated my cast iron keel with epoxy resin before I faired and painted it. 

You ARE wearing a respirator, right???

Dust mask and hearing protection, yes. I do not wear the organic vapor rig for sanding although one could easily argue in favor of it if one smells styrene like I did. Full-face with positive airflow would be awesome.

Saw some advice at West Systems about applying epoxy and then 'sanding' it into the bare metal surface while still wet. I think the idea is to displace and encapsulate random bits before they rust. Thye also have a 422 barrier coat additive which seems to give the epoxy a bit of a paint-like body.

[Noemi - Ensenada 20]

I did both of those things West Systems advises when I did my keel.

[Spot]

Thanks Noemi. I should sit down with a cup of coffee and read all of your and CB's notes again.

[Noemi - Ensenada 20]

I think "epoxy, wire brush while it's wet, then epoxy with barrier coat" is an alternate to "Ospho, then coal tar epoxy."  Two different methods, both of which work well.

[Spot]

It worked out in my recent travels to secure a can of West System 422 barrier coat additive.
Plan is to 'sand in' one coat plain epoxy coat followed by 2 coats with the additive and allow a longer cure then sand for tooth and coat with alkyd enamel paint. I will return the rusty metal primer to the store unused.
After leaving the keel sit for a week, I have a little discoloration.
Am I identifying the spots that need rework (sanding and re-treatment) with phosphoric acid correctly?


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[Charles Brennan]

Spot, you are definitely identifying the rework spots, correctly.
You also have me a little confused, about your plans to "sand in" a coat of plain epoxy.
The biggest problem with oxidation, is that it occurs as soon as there is any oxygen present.  The whole point to phosphoric acid treatment is to create a chemical layer of iron phosphate where the existing oxygen is bound up in the iron and phosphor (FePO4) and additional external oxygen (i.e. on the surface) cannot attach and oxidize (read: rust) the Iron.

Noemi's method of sanding under epoxy while still wet, is an attempt to deal with the fact that the keel started oxidizing (rusting) as soon as it was sandblasted, since oxygen was free to attach to the Iron. By sanding, this assured that most of the oxidized Iron was sanded/wire-brushed from the surface and no new oxygen could attach, since it was now protected by the still-wet epoxy.
I have no quarrel with this method; indeed, I am forced to point out that Noemi has only had to re-build her keel once, whereas I have required two attempts at it.    
(Although in my snarkier moments, I might mention that my keel has seen a lot more water, for a lot more years, than her keel has!) 

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In the above pic, you are showing the same things I dealt with on my own keel.
My first attempt at applying the Phosphoric acid, after wetting it down and observing it the next day, showed just how much rust I had failed to grind off, that required remedial grinding.
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But after more grinding and about two more applications: SUCCESS!! 
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Based on what I see from your pic:
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At this point, I would forego your cool 3M wheel and switch over to something like a Dremel tool with a small stainless steel wire brush.  To remove the pitted rust you are showing, would require grinding the entire surface to the depth of the deepest rust pit.  You would be better served by concentrating on those small areas with a small wire brush.  The thing I liked the most about using Ospho, is that it really kept you honest and exposed even the smallest amount of Iron Oxide, on the surface of the keel. Once all free oxygen is bound to the Iron Phosphate, there is no longer any possibility of rusting, and therefore, no need for "sanding in" under the epoxy.

If you think about it for a minute, the sanding would in fact, damage that thin molecular coating of Iron Phosphate, and while safe under the wet epoxy, if the keel was ever scraped through the epoxy where the Iron Phosphate had been scraped, it would immediately begin rusting again.

The two mistakes I made in my 1999 keel refurb were:
1) I applied fairing epoxy to the treated metal, before applying the coal tar epoxy.  The fairing epoxy was highly water absorbent and did not take too many "dings" grounding on reefs and rocks and whatnot, before I started getting significant rust. 
2) I laid the keel on its side and applied things, one side at a time. This caused two "seams" front and back and obviously, the front seam getting the brunt of navigational errors ("I know every sand bar in the Bay, like the back of my hand!" BUMP!! "There's one, now!!")  rusted first and opened up, then allowed the epoxy to de-laminate from the keel over time. That could not have happened had I applied the coal tar epoxy first and in a total coating (not one side at a time) then faired it with an epoxy filler,  after the fact.
I corrected both those errors on the 2nd refurbishment.

It looks like you are very close to being done with the Ospho treatments.
I would recommend against "sanding in" under an epoxy coating.  I don't feel it would provide enough "tooth" for a better mechanical epoxy bond and would risk the cohesive integrity of that Iron Phosphate coating.
The West System 422 barrier coat additive sounds like an excellent addition to protect the keel from bumps and scrapes.  The coal tar epoxy I used does not really get hard like some epoxy coats do and is, in fact, more "rubbery" in feel and as a result, bangs only dent it a little and do not penetrate through to the Iron.  That West System 422 sounds like it will behave in much the same manner.

One guy's opinion,
Charles Brennan

[Spot]

Thanks Charles, I appreciate your detailed explanations!
 
 I am thinking of quizzing West System about this too since 422 is involved. I have yet to contact them directly but have appreciated their various how-to's online: https://www.westsystem.com/instruction/tutorials/

[Spot]

A quick update:
Work, travelling, weather...conspiring to keep me away from the boat, rather than under the boat with the goal of sailing in it.
I had a nice visit with my company's rep at 3M and we narrowed down the product selection to 4000UV or 5200 for the keel bedding joint.
I also had a nice visit with a technical advisor at West Systems concerning the epoxy and barrier coat powder.
I decided to give it a go last night. My leftover resin had crystalized in the container so I gave it a hot tap water bath, changing the water every 15 minutes or so, until it became clear and liquid. I tinted that coat red and did coat #1 on the mating surface last night. Early this morning I got up and mixed a smaller batch with the 422 barrier coat powder which tints the mixed epoxy gray. The epoxy seemed 'runny' but set up fine so I am thinking I will need to lay the keel on its side and coat the 2 big flat 'up' sides (outside and inside slot), flip, and repeat.

Pic is part way though the early session. I like the way the red brush pulled out of the container, leaving it clean for the next batch When it pulls out like that, I have a high level of confidence in my measuring (by weight) and mixing.

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[Noemi - Ensenada 20]

Charles is right - the "sand wet epoxy" method and the "Ospho and then coat" method are two different ones.  You probably don't need to use Ospho AND sand wet epoxy.

And Charles' keel has seen a lot more SALT water than mine has (none).