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 Tips & advice for keel rust repair & fairing
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Volksaholic
1st Mate

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Initially Posted - 03/29/2022 :  10:42:51  Show Profile  Reply with Quote
I apologize for cross-posting. I know that's bad form on most forums. I thought this was appropriate for the general sailing forum, but maybe it got no traction because it's boat prep rather than sailing.

I've got an '81 Catalina 25 with the iron fin keel that was kept in the Great Salt Lake for a number of years and then stored on the trailer for the last 5 years due to declining health of one of the owners. I'm scraping the bottom paint to start prepping to refresh it but there are also some fairly deep blisters of rust on the keel. I'm looking for advice for the best way to repair them. If it matters, it looks like I'll be storing it on the hard most of this summer at a freshwater lake while we see if Utah is going to recover from our drought or if the GSL turns into a mini Sahara Desert. I'm interested in knowing what you've all had good experience with both the repair/prep and products that will be appropriate for dry storage combined with freshwater sailing.

My gut and reading suggests that I start with a stiff wire brush on a grinder. I've also done a little more banging to get down to solid metal and I think I need to strip the entire keel to bare metal and start fresh because I have yet to find pristine iron. There's no pitting on the leading edge but the iron is rusted underneath the factory fairing.

I've used rust converter type products (usually phosphoric acid, IIRC) on auto rust with good result but I don't know if that's appropriate with the filler(s) I'll need to re-fair the keel. Some folks have been recommending a rust-converting primer, which I used on my Laser trailer when I rebuilt a few years back. I like the idea of that as long as it doesn't risk a weakened bond between the filler and iron. I was planning on a thin epoxy in the pits followed by thickened epoxy but I'm finding several suggestions of thickened filler to avoid dealing with mixing in and potentially breathing silica. I was curious whether I should fiberglass over the iron/filler but everything I'm reading indicates that an appropriate paint over the epoxy is sufficient... no need for any fiberglass. My intuition suggests that I at least tape the leading, trailing, and bottom edges for a little abrasion resistance but I'm not seeing anything that suggests that's a common practice and I'm not looking to over complicate the job if it doesn't provide any benefit.

Does that seem like a solid plan or is there a better approach to doing this repair? I did call around last fall to see if I could find anyone who would sandblast it but came up empty. I was surprised that I didn't find any other questions about this on this forum because I can't imagine I'm the first one to deal with it, but either I wasn't searching properly or everyone else already knows what to do. I did find some helpful posts on the r/sailing subreddit.

Since I posted in the general forum I took some pics to help communicate the extent of the damage. I'm finding what looks like factory filler/bondo in the upper half of the keel, and what looks like a piece of angle iron embedded in the casting. I haven't checked to see if it lines up yet but I'm guessing that's an anchor for the keel bolts. In any case, I think I need to dig all the filler out because the water has gotten beneath it. I found some fairly deep crust/pits that I haven't measured but I'm thinking they're probably 1/4" deep. The bottom edge is also really bad and I'm considering how I can prop the boat a few inches to pull the bunk (correct term?) beneath the keel to replace it and clean up the keel. Otherwise I guess I've got to prep everything else and then figure out how to get the bottom of the keel from a crane or something... haven't quite sorted that out.

I'm not sure the best way to share the pics so I'll try adding an Imgur link: https://imgur.com/a/Ledvrxf

Thanks in advance for suggestions, advice, warnings, or mockery for buying this beast in the first place. :)
Paul
1981 Catalina 25 TR/FK

Paul
1981 Catalina 25 TR/FK
Soon to be named either Fiddler's Dream or Fool's Errand depending on what it takes to get her into shape

Steve Milby
Past Commodore

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Response Posted - 03/29/2022 :  12:52:16  Show Profile  Reply with Quote
Some people advocate stripping the keel to bare metal. My thinking is you should do only what you have to do, and no more.

The casting is fairly crude. I believe Catalina originally coated it with black, coal tar epoxy and filled the depressions with an epoxy filler. I don't know how widespread the damage is to yours, but I tapped all over the surfaces of the keel with a hammer. Solid metal coated with firmly attached filler has a ringing sound. Loose filler with severe rust beneath it sounds dull. I used the hammer and a chisel to chip away all the loose fairing compound and rust. I used an electric drill with a wire brush to clean it better. I didn't keep at it until I saw bare, shiny metal. If there was still solidly attached coal tar epoxy or filler, I was satisfied. I only removed what was necessary to reach a solid surface. I sprayed rust reformer over it, just to protect any bare metal until I could complete the repairs. Then I filled all the depressions and faired the keel with a good quality epoxy marine filler. Getting it smooth with an electric sander is way too slow, so I used a 4 1/2" angle grinder to grind down the high spots, and then finished smoothing it with an electric sander. I did that for many years and still got blisters on the keel until I attached a sacrificial anode to the keel, and that seemed to have stopped the problem. (zinc for salt water and magnesium for fresh water.)

Steve Milby J/24 "Captiva Wind"
previously C&C 35, Cal 25, C25 TR/FK, C22
Past Commodore
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Steve Milby
Past Commodore

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Response Posted - 03/29/2022 :  13:13:36  Show Profile  Reply with Quote
I just saw some of your photos and it's fairly widespread, but I'd still only remove what's necessary to find a solid surface. If it's all that loose, so be it. When it's done, coating it all with 5-6 coats of barrier paint might be a help.

Steve Milby J/24 "Captiva Wind"
previously C&C 35, Cal 25, C25 TR/FK, C22
Past Commodore
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Volksaholic
1st Mate

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40 Posts

Response Posted - 03/29/2022 :  14:12:32  Show Profile  Reply with Quote
Thanks for that feedback. So far I've hit it with a paint scraper followed by a geologist pick. I only hit the places where it was obvious there was a problem and was pretty disappointed with what I see. Maybe I won't strip it all down, but I suspect it will be extensive enough that it might be just as easy to strip it all. You answered another question I keep forgetting to answer; should I install a sacrificial anode. It seemed like it would be a good idea with an iron keel but this is the first one I've owned. I usually have the pleasure of helping other people push their boats to the limit without the time and expense doing the maintenance work. :)


Paul
1981 Catalina 25 TR/FK
Soon to be named either Fiddler's Dream or Fool's Errand depending on what it takes to get her into shape
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Leon Sisson
Master Marine Consultant

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Response Posted - 03/29/2022 :  20:38:59  Show Profile  Visit Leon Sisson's Homepage  Reply with Quote
Paul,

Here are some search terms and links into the vast store of knowledge and experience accumulated on this website.

For example, I searched on "keel sand blasting" and found a wealth of threads which included both fin and swing keel refurbishing, fin keel sump issues and repair, etc.  I recommend checking the [X] Archived Posts box for best results.

For example, "Keel Bolts, Bilge and plywood stiffener".
 
Searching on "fin keel rust" might also turn up some interesting reading.
 
Here's a link to an iron keel refurb procedure I've used: 
"Catalina 25 Swing Keel Refurbishing Procedure".
 
Keep in mind, what works best for one boat, owner, and sailing conditions isn't going to be perfect for all boats, owners, and situations.
 

Leon Sisson
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Volksaholic
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Response Posted - 03/30/2022 :  09:11:36  Show Profile  Reply with Quote
Thanks for the input and links, Leon. You're correct that I didn't think/know to search "Archived" articles, so that coupled with insufficiently broad search terms failed to turn up the "Keel Bolts..." discussion.

I find it interesting in the "Catalina 25 Swing Keel" article the author hit it with phosphoric acid after stripping to bright metal. From my experience and research with phosphoric acid based rust converters they only act on rust. I guess it makes sense... it won't damage the bare metal and it will stabilize rust in pits that are missed by blasting/grinding. I wish I could find a good place to blast it. There are places that I think sandblasting is the wrong approach but in this case I think it would be ideal.

I had considered using POR15 because it's well regarded in automotive repair but I was watching a video where someone had problems with coal tar epoxy adhesion to the POR15. Granted, that could just be their prep/process/product, but if a straight rust converter followed by epoxy/filler is an accepted approach that's the simpler and cheaper way to go. POR15 is great stuff but it's not cheap.

I also found it interesting that he did the fiberglass wrap. Since that doesn't seem to be the typical or recommended treatment for an iron keel, it does make me think I might follow through with a fiberglass reinforcement on at least the leading edge and bottom of the keel to add some durability to the epoxy/fairing. The reality, though, is that by the time I've done the work to get to that point I'm probably going to be seriously burned out on keel prep and won't want to add an optional step! :)

I appreciate the input. For the time and money it's going to cost I'd like the rust repair to be mostly a one-and-done job and future maintenance to be limited to touching up epoxy damage and refreshing the paint.

Paul
1981 Catalina 25 TR/FK
Soon to be named either Fiddler's Dream or Fool's Errand depending on what it takes to get her into shape
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Steve Milby
Past Commodore

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Response Posted - 04/06/2022 :  07:17:55  Show Profile  Reply with Quote
Cast iron keels in that era were not wrapped, from the factory, in fiberglass cloth. 2-3 years later, cast iron keels were fully encapsulated in fiberglass. The benefit of encapsulation was that the keel was smoother. The drawback was that, if you hit a rock, it made repair much more complicated. If you damage the filler, you just chip away the loose material, apply new filler, smooth it, and go sailing. Without seeing the keel, my inclination would be to smooth it with filler, without applying glass mat or cloth.

Steve Milby J/24 "Captiva Wind"
previously C&C 35, Cal 25, C25 TR/FK, C22
Past Commodore
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Volksaholic
1st Mate

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Response Posted - 04/06/2022 :  11:40:37  Show Profile  Reply with Quote
Thanks Steve... I appreciate the input. While smoother is better, I don't expect this to be a fast boat. :) Stabilizing the rust and having a decent fairing job is enough. Unless something/someone changes my mind, I've written off glassing the entire keel; I'm not looking to unnecessary work. For the record, my prior experience is making and repairing blades on my dinghies, in which case I always tape the leading and bottom edges with a little extra fiberglass. This keel is a bit of a bigger challenge, and while it's not rocket science it's very helpful to learn from others' experiences so instead of encountering the usual noob mistakes I can invent new ones.

Paul
1981 Catalina 25 TR/FK
Soon to be named either Fiddler's Dream or Fool's Errand depending on what it takes to get her into shape
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