My boat has a cast iron keel and last time it was out I noticed a number smallish spider like cracks with telltale brown colour (due to underlying water intrusion and rust) which weeped a tiny bit. I took the angle grinder to 1/2 dozen or so of these spots thinking the steel keel would come to light a couple of mils under whatever fairing was there but then took fright when I went down 6 or 7 mil and was not getting to Steel. I had a lot to do that slip so just let them dry a bit then painted them with Altex Primashield then antifouled leaving any filling or fairing for next time.

Well next week is next time so the moment of truth has come. Wondering what's the best procedure to fill these little divots (approx 50mm diameter max) will be this time. I'm thinking to bog them with epoxy presumably after hitting them lightly with an angle grinder again. Presumably some sort of undercoat will be necessary and then use of an epoxy which will stay put on a vertical surface and can be reasonably readily sanded to get it smooth. Any recommendations for procedure and products to use?

Thanks.

The best CI keel protection from new was black (coal) tar epoxy in 5 coats. But this is banned now. Good general keel maintenance article here

marskeel.com/your-guide-to-keel-maintenance/

Previous post here

www.seabreeze.com.au/forums/Sailing/General/Paint-Product-for-Cast-Iron-Keel-?page=1

Good article on patch repairing here

www.practical-sailor.com/boat-maintenance/keels-minor-maintenance-and-repair

And a more extensive re-coating here - "Plaster" in Setp6 title should be "epoxy filler"

www.boatsnews.com/story/20344/my-keels-rusting-what-can-i-do

Many on-line links indicate etch priming the CI patches before epoxy barrier coating -

Select to expand quote

r13 said..
The best CI keel protection from new was black (coal) tar epoxy in 5 coats. But this is banned now. Good general keel maintenance article here

marskeel.com/your-guide-to-keel-maintenance/

Previous post here

www.seabreeze.com.au/forums/Sailing/General/Paint-Product-for-Cast-Iron-Keel-?page=1

Good article on patch repairing here

www.practical-sailor.com/boat-maintenance/keels-minor-maintenance-and-repair

And a more extensive re-coating here - "Plaster" in Setp6 title should be "epoxy filler"

www.boatsnews.com/story/20344/my-keels-rusting-what-can-i-do

Many on-line links indicate etch priming the CI patches before epoxy barrier coating -

Thank you very much :-)

It's a shame that you brought this up - you've reminded me that I need to do the same thing. My list of haul out week jobs is getting longer. More like haul out 6 months at this stage...

How big is your boat and is it feasible to take the keel off to do the work? My club doesn't allow sand blasting in the work bay and scrabbling around under the boat with an angle grinder sounds awful (and would probably create more airborne dust than blasting anyway).

If it was possible to undo the keel bolts, remove the keel and cart it away to be sandblasted it might result in a better job. Plus there would be the opportunity to inspect/replace the keel bolts.

Manhandling 400+ kg of steel might be tricky though...

Select to expand quote

julesmoto said..
My boat has a cast iron keel and last time it was out I noticed a number smallish spider like cracks with telltale brown colour (due to underlying water intrusion and rust) which weeped a tiny bit. I took the angle grinder to 1/2 dozen or so of these spots thinking the steel keel would come to light a couple of mils under whatever fairing was there but then took fright when I went down 6 or 7 mil and was not getting to Steel. I had a lot to do that slip so just let them dry a bit then painted them with Altex Primashield then antifouled leaving any filling or fairing for next time.

Well next week is next time so the moment of truth has come. Wondering what's the best procedure to fill these little divots (approx 50mm diameter max) will be this time. I'm thinking to bog them with epoxy presumably after hitting them lightly with an angle grinder again. Presumably some sort of undercoat will be necessary and then use of an epoxy which will stay put on a vertical surface and can be reasonably readily sanded to get it smooth. Any recommendations for procedure and products to use?

Thanks.

To remove thick bogg on steel my preferred method is to hit it with a hammer and maybe an old chisel. I've seen jotafair hold up well in immersed conditions but I'm sure any under water fairing compound mixed with epoxy will be good the trick will be to remove ALL the rust. If you want to be extremely thorough all the bogg could be removed and the rust with a needle scaler, but I hardly see the point as it not going to sink the ship, the cast is solid yes ?

Select to expand quote

woko said..

julesmoto said..
My boat has a cast iron keel and last time it was out I noticed a number smallish spider like cracks with telltale brown colour (due to underlying water intrusion and rust) which weeped a tiny bit. I took the angle grinder to 1/2 dozen or so of these spots thinking the steel keel would come to light a couple of mils under whatever fairing was there but then took fright when I went down 6 or 7 mil and was not getting to Steel. I had a lot to do that slip so just let them dry a bit then painted them with Altex Primashield then antifouled leaving any filling or fairing for next time.

Well next week is next time so the moment of truth has come. Wondering what's the best procedure to fill these little divots (approx 50mm diameter max) will be this time. I'm thinking to bog them with epoxy presumably after hitting them lightly with an angle grinder again. Presumably some sort of undercoat will be necessary and then use of an epoxy which will stay put on a vertical surface and can be reasonably readily sanded to get it smooth. Any recommendations for procedure and products to use?

Thanks.

To remove thick bogg on steel my preferred method is to hit it with a hammer and maybe an old chisel. I've seen jotafair hold up well in immersed conditions but I'm sure any under water fairing compound mixed with epoxy will be good the trick will be to remove ALL the rust. If you want to be extremely thorough all the bogg could be removed and the rust with a needle scaler, but I hardly see the point as it not going to sink the ship, the cast is solid yes ?

Yes pretty sure it's solid though some say it is filled with lead.

Select to expand quote

Microbe said..
It's a shame that you brought this up - you've reminded me that I need to do the same thing. My list of haul out week jobs is getting longer. More like haul out 6 months at this stage...

How big is your boat and is it feasible to take the keel off to do the work? My club doesn't allow sand blasting in the work bay and scrabbling around under the boat with an angle grinder sounds awful (and would probably create more airborne dust than blasting anyway).

If it was possible to undo the keel bolts, remove the keel and cart it away to be sandblasted it might result in a better job. Plus there would be the opportunity to inspect/replace the keel bolts.

Manhandling 400+ kg of steel might be tricky though...

I don't think things are that bad. It's a Northshore 38 and apparently other owners pretty much just ignore it or do minor spot fixes and have been doing so for decades. Be interesting to see what it looks like in the areas that I just primed last time