Issues with Coppercoat on cast iron keel - need some advice

[benzy]

We have a Moody 376, which has a bolt-on cast iron keel. The boat’s hull had been coppercoated many years ago and the keel was regular anitfouled.

We decided to bite the bullet and get the whole thing redone with coppercoat in an attempt to avoid having to haul out each year. We figured if the coppercoat lasts 4-5 years then the extra expense upfront will have been cancelled out and every year after that is a bonus.

The main concern, having read what I could on the internet, was the preparation of the cast iron keel. The require for it to be treated properly to avoid rust is crucial. We got a number of quotations from various yards in Greece (where we are). Based on a number of cruising friends giving very positive feedback about a particular yard, we decided to go with them.

They did the following:
- Sanded back the hull
- Sand blasted the keel all the way back
- Used epoxy filler to fill the expected unevenness of the keel
- Applied 4 coats of epoxy primer to the keel
- Applied 4 coats of coppercoat over the hull and keel

They did the work over the course of 5 weeks. They let the boat dry out for about two weeks before starting work on it. They were supposedly watching the humidity and picking the best time to do the work. They sent progress photos as they went.

We returned to the boat just before they applied the coppercoat, so I had a chance to see the primed keel and to me it looked really good - smooth finish (but I’m not expert of course!)

Anyway, we launched and here we are two weeks later and there appears to be a problem. On the port side of the keel there are 12 rust spots that have appeared - like pin holes where rust is “oozing” out. On the starboard side there is on pin hole spot, and one section where a rust line is appearing along the hull-keel join.

Having reread other people’s experiences with coppercoating a cast iron keel, it seems this is not good, especially after only two weeks of being in the water. The flip side is people always say “cast iron keels are impossible to keep rust free to so things like this are inevitable”.

We don’t have an opportunity to go back to the yard that did the work, so that is not an option.

I’m trying to figure out:
1. Is this normal, or considered an acceptable outcome after two weeks in the water?
2. Is it something that needs to be fixed (ie: I can live with the rust spots, but I can’t live with the coppercoat itself becoming damaged and flaking off)?

Thanks

[barnakiel]

Go down check if the spots are in line. If so, this may be the seam. There is some flex there and depending on the laminate / slab joint the movement may break off / crack the epoxy, etc.


Even without cracking, the joint area, if wet, dries last. It is not uncommon to see rust pin points reappear in this area after very short time in the water.


As working underwater is only limited to an inspection, what you are doing is go to the boatyard and lift her. Inspect and fix. Normally, this is just a spot repair, not overdoing the job again.


Beter yet, take images now. Take more images in about a month. See if more spots appear. If so, it may be required to redo the keel area - there may be excess humidity in the iron slab.


Has the slab been sandblasted?


A well cleaned slab, covered in many coats of epoxy should last spotless for years. Hence by guess re the joint.


b.

[billknny]

One thing you did not mention in your description of the yard's work: the timing.

When coating cast iron it is absolutely critical that the initial sealing coat go on immedietly after blasting or grinding to silver-bright metal. Even a delay of an hour can be too long. If it sits overnight exposed to air, the surface will oxidize and the coating fail. Even if it looks bright and clean, microscopic rust will have started, and that’s the beginning of failure.

Most people who do it right work on a few square feet at a time.

The issue is not coppercoat, it has been applied successfully to many cast iron keels. The failure you are seeing would have happened with any bottom paint.

A proper cast iron finish job will show no rust at all for years, not at the joint either.

[gmakhs]

Hello ,
I am not an expert , older boats like mine 1984 have the cast iron keel all covered with a layer of putty , I don't know if it is to fair the keel shape or to water proof the keel , but mine had rust after all those years only in the botton where it touches the ground , I did fair it and use iron putty on it 3 years ago and no rust have appear .
After the putty the keel has primer and anti fouling, for me it seems a good way to protect your keel from copper coat (if it create a problem *I have no idea ) and from water intrusion.

[benzy]

Thanks for the replies.

The keel slab was sand blasted.

As for the timing, I’m not sure. I can ask the yard but obviously can’t trust their answer considering they will know something is wrong.

They did send an email with photos of the sand blasted keel, and the following day they send another email with photos of the epoxied keel (this proves nothing except that they at least did it with 24 hours - but as you say that is too long to wait).

[gmakhs]

If you gonna wait , it's better to use a rust stabilizer like the ones they use on construction.
The epoxy won't waterproof the keel properly ,I have seen a lot of rusty epoxied keels.

[fstbttms]

Why would you have to haul annually for new paint? Any decent hard anti fouling paint, properly applied, will provide 3+ years of good performance.

[billknny]

Originally Posted by gmakhs

If you gonna wait , it's better to use a rust stabilizer like the ones they use on construction.
The epoxy won't waterproof the keel properly ,I have seen a lot of rusty epoxied keels.

I'd disagree, at least a little. The right thing to do is to EXACTLY follow the instructions for the products that you are using. I am not aware of any marine coatings that recommend the use of generic "rust stabilizers" under their products. The chemistry of these coatings is finally tuned and should not be messed with, if for no other reason than any claim for failure will be denied flat out by the manufacturer if you did not follow directions.

Any cast iron keel that shows general rusting has a failed coating, and should not be tolerated. The coating might be old, it might have been misapplied, it might have been damaged.

Epoxies certainly CAN work, but there are many kinds of coatings that are called "epoxy" and not all of them are suited for coating underwater cast iron. So can some other types of primers if they are appropriate for the job, and are applied as recommended.

On the general outside surface of the keel, rust is not a short term problem, but...

Rust in the gap between the keel and the hull has the potential for causing very serious damage. When iron tuns to rust, it expands, a LOT. Up to 40 times in volume. That expansion is irresistible. It can distort and break the fiberglass hull it is attached to. It can pull keelboats through the bottom of the boat. Rust leaking out of the hull/keel joint needs to be fixed, or it has the potential to end the life of the boat.

[gmakhs]

I agree with you but in a boat like mine which iron filler putty have been used and it works I don't see why not to use the stabilizer..

About the keel bolts some older quality build boats like Sweden yachts 34c have a gap between the keel and the hull to absorb the expansion if it happens

[nepal]

I treated my keel the same way some 4 years ago. Still happy with it. There is some rust between keel and hill. Many boats have it.. My saildrive is not attacked by electrolyses. I don't see a reason to worry.

I wonder how you are sure that whatyou see are rusty' pinholes. Coppercoat is brown and turns on to dark green.

Don't forget to haul the boat for replacing the anodes

[fstbttms]

Originally Posted by nepal

Don't forget to haul the boat for replacing the anodes

Yes, by all means spend half a day and hundreds of dollars doing a job that a diver could do in 15 minutes for a fraction of the price.

[Clivevon]

Hi. Moody 376 - nice boat. I have a Westerly Conway with a cast iron fin which has twice been copper coated.
I am going to assume your problem is not with a flexible fin to hull joint.
Back in 2000 the yard in Mallorca where we were then was unable to successfully Coppercoat the fin. Can't remember the exact symptoms but basically the coating wouldn't stick for any length of time. We ended up anti fouling the fin yearly thereafter and just Coppercoating the grp hull.
Came time to renew the Coppercoating on the hull in 2013, now back in UK. Research then said the cast iron fin needed to be totally stripped back to clean bare metal then coated with a completely inert material to completely isolate it before applying Coppercoat. I seem to remember ceramic microbeads In epoxy or some such being mentioned.
The U.K. Yard that did the job (JWS in Southsea ) didn't use that in the end. They recommended and used some other product they were familiar with that did a similar job. Unfortunately can't remember the name of it and am currently away for 2 weeks without access to records. Anyway. 5 years on all still seems well and the Coppercoat is still on the fin as well as the hull.

Hope that is helpful as to what to expect?.

[captlloyd]

Rather than epoxy primer then antifoul, I would want a finishing epoxy on top of the primer, then antifoul. All paints to some degree can be penetrated by water, antifouling may not be all that waterproof. Latex comes very close to being waterproof.

[Snowpetrel]

From your description it sounds like they may have put the epoxy fairing straight onto the sandblasted keel. Normally you would paint it first with several coats of a good quality epoxy primer, then fair with epoxy then paint again to seal up the fairing before the final coats.

[fstbttms]

Originally Posted by captlloyd

...antifouling may not be all that waterproof.

Of course anti fouling paint is not waterproof. It works by not being waterproof. Water penetrating the paint matrix is how its biocides are leached out. Coppercoat however is a water soluble, copper-loaded epoxy (and therefore not a "paint") and works somewhat differently.