Cast iron keel

Aug 8, 2009
6
2 373 RI
I have a Beneteau sailboat with a cast iron keel. It has rusted. Can someone tell me how I would fix this. Thanks
 
Jun 2, 2007
403
Beneteau First 375 Slidell, LA
Well, how much rust? General procedure for extensive rust is to sandblast back to bare metal, then immediately (do not wait) seal with epoxy. Old schoolers like what's called coal-tar epoxy. For spot repairs on a less affected keel, you could sand or grind away the rust, maybe apply rust converter (phosphoric acid), then seal with epoxy. After doing either of the above, fair the keel using epoxy thickened with microballoons and sand to taste. Be prepared to do it again the next time you haul out, but if you did a good job the first time, it won't be as bad.
 
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Jul 7, 2004
8,402
Hunter 30T Cheney, KS
There are many threads and several opinions on this. I used the POR15 process on mine this Spring. I'm curious to see how it did when we haul out this Fall.
One benefit of getting rid of rust is the keel is much smoother so maybe a little faster.
 
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Nov 8, 2010
11,386
Beneteau First 36.7 & 260 Minneapolis MN & Bayfield WI
My First 260 has a 6 foot draft lifting iron keel. After 17 years and probably bottom several impacts, there was some rust coming through.

In the off season I had the entire bottom and keel soda blasted down to bare gelcoat and iron. The keel was ospho treated, epoxied with Interprotect 2000E (pix taken) and faired and epoxied again before bottom paint. I expect it to last 20 years.

IMG_0595.JPG


You can see some of the slight surface imperfections from the casting process. The fairing gets rid of all of that.
 
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DougM

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Jul 24, 2005
2,242
Beneteau 323 Manistee, MI
I had some blistering on the kee ,of my B323 that was attributed to a manufacturing defect in the keel coating process. I ground the keel down to bare iron and recoated with Interprotect 2000E.
Immediately after that, I bottom painted with VC17, and recoat with VC17 every spring . After five years, I have not yet seen any new blistering or rust. I just had the boat hauled out for winter storage this week and the keel still looks fine.
 
Dec 31, 2016
319
Beneteau Oceanis 351 Charlottetown
Blistering on a cast iron keel is only on the surface, as it cannot penetrate into the keel itself or cause any harm, it's all about looks.
 
Sep 20, 2014
1,320
Rob Legg RL24 Chain O'Lakes
Looks and performance. A rusted keel will not work properly, as the water does not stay attached to the back side.

Grinding does not work, unless you have an endless amount of time to work on it. rust causes pitting. If you grind, you have to take away a lot of metal to get to the rust in the pits. Sandblasting is fine enough to get into the pits. Last time I did mone, I coated it with cold galvinized paint. that was 2 tears ago, and it is still pretty good. There is a small amount of stains where it gets scraped in the sand from beaching, but the rest of it has held up well.
 

Gunni

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Mar 16, 2010
5,937
Beneteau 411 Oceanis Annapolis
This question comes up...and get's answered on a regular basis. Do it right and you will not have to worry about rust again unless you grind the keel across stone and metal. Do it wrong and you be out there doing it again, year after year. Doing it right only requires the proper prep, materials and application. Jackdaw describes the method used by pro marine tradesmen for saltwater. Either Interprotect2000 or Interprotect HS will result in a hard substrate for good adhesion of your bottom paint. HS just means high solids and goes on thicker. Ospho is a great way to assure that any micro rust is converted to iron and you have a good base for the epoxy primer. Make sure you know how to work with epoxy and apply with the 'hot coating' technique. Get a build to the specified 10 mil. Interlux paints has a great series of guidance documents on their website.
 
Feb 8, 2014
1,300
Columbia 36 Muskegon
Get the loose stuff off by grinding, blasting, etc. Then douse liberally with Ospho and let stand overnight. Then proceed with faring and paint. You'll find Ospho in ge paint isle at Home Depot et al and its cheap. We use it before painting all bare steel on the commercial boats snd the psint stays on very well. Works well on old cars too.
 

Artey1

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Jul 18, 2019
165
Hunter 34 Oklahoma
Sorry to bring up an old thread but have a question about topcoating over OSPHO. What kind of prep if any are you doing before topcoating the OSPHO? Just washing/light sanding the residue off? Grease/wax remover? I've read lots of issues about primers not sticking. I have grinded and coated with OSPHO and am letting it cure. Need to get topcoated before rain later this week. Can I put Interprotect straight over the OSPHO and expect good results, then fair out the keel from there?
 
Mar 20, 2016
594
Beneteau 351 WYC Whitby
I did that to mine for 3 years ospho and 2000e and kept getting rust every year. 2 years ago ospho ,por15 ,then 4 coats of 2000e ,last coat of 2000e when still tacky I painted the micron. My buddy too kept getting rust ,we then added 2 tear drop zincs to the keel ,one each side 2 years ago, no rust now 2 years straight for both of us
 
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Artey1

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Jul 18, 2019
165
Hunter 34 Oklahoma
I did that to mine for 3 years ospho and 2000e and kept getting rust every year. 2 years ago ospho ,pur15 ,then 4 coats of 2000e ,last coat of 2000e when still tacky I painted the micron. My buddy too kept getting rust ,we then added 2 tear drop zincs to the keel ,one each side 2 years ago, no rust now 2 years straight for both of us
I was planning to just do Interprotect HS over the OSPHO, its like 2000e but thicker so you don't have to coat as many times to get the 10 mil thickness needed, then I was going to fair with interfill, and recoat with Interprotect again, then hard ablative probably. I'm in fresh water, I'm assuming you are in salt? How did you attach the zincs? Drill through or what?
 
Mar 20, 2016
594
Beneteau 351 WYC Whitby
Drilled and tapped then 2 stainless Allen head cap screws.I'm also in fresh water
I use micron which is pretty hard
 

Artey1

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Jul 18, 2019
165
Hunter 34 Oklahoma
Drilled and tapped then 2 stainless Allen head cap screws.I'm also in fresh water
I use micron which is pretty hard
Back to my original question though, did you do anything special before putting the POR15 over the OSPHO? Wash it or scrub with brillo, or just let it cure and then straight to putting on the POR15?
 
Mar 20, 2016
594
Beneteau 351 WYC Whitby
Washed with water then por15 it cures better with moisture I believe if memory serves me, then sanded lightly por15 then 2000 e if you use por15 don't get it on you ,you will have to sand it off
 
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Vilma2

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Nov 15, 2019
1
Beneteau 351 Espoo
Where in the keel did you install the zinc? Any hydrodynamic considerations? How big a zinc would be enough, with annual checks?
(I have experience of rusty keels but new to Oceanis 351 and this forum here)
 
Mar 20, 2016
594
Beneteau 351 WYC Whitby
On my 351 I installed a teardrop style on each wing with the narrow part facing forward.On my buddies 375 we installed one on each side of the keel midway same way narrow part facing forward. Mine has lasted 2 years and needs to be changed this year, however I'm only in the water from end of April to end of Oct in fresh water
 
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RitSim

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Jan 29, 2018
406
Beneteau 411 Branford
I stripped a cast iron keel on a former boat (Pearson P-26) . Cast iron tends to be rough on the surface so sanding/grinding is only for small areas. Sandblasting, as mentioned above, is the best - and the most expensive. I used a needle scaler. The tool has -15-20 rods that are impacting the area. I had the ability to get into most rust pockets. I used Navel Jelly (which sounds similar to Ospho) until all of the rust was gone. Then 4 coats of 2000E followed by carefully applied fairing compound (to avoid any metal sanding damaging the 2000E) and then bottom paint. I saw the boat 8-10 years later and there was still no rust.