steel keels -inside and out

[EddBee]

I have just come into possession of a Kingfisher 30s, which i am- overall- very pleased with. As you might know the keels are steel with lead at the base and were (previously- since altered it seems) used as fuel tanks. After a period of neglect there is work to do on the external steel and i've found advice on here about how to tackle that, but should i be worried about the internal surfaces of the keels? As i see it this is now an open surfact of steel, maybe with some old diesel and no doubt water slopping about, potentially ripe for corrosion that would go on without me being aware of it. There's no access, so if it does need sorting it's going to be a job and a half. My thoughts are to drain and dry as best as possible, treat with rust converter if possible and (since they are meant to be ballast) fill with.. something. Epoxy and lead shot? just epoxy? some kind of anti corrosion agent? Or am I over thininking this? -this is quarter inch steel, but then the boat is nudging 50...
Thoughts?

 

[srm]

The old way of filling small void spaces to avoid corrosion on steel yachts was by filing with hot bitumen. It was also be used to encapsulate lead ballast in steel hulls. Probably a lot cheaper than epoxy. There can also be problems of exothermic reaction if some types of epoxy is mixed in a largish volume.
I would not be inclined to add extra ballast, but the inside of the keels need to be sealed to prevent oxygen and/or humidity reaching the steel.
An inspection hole could be cut in the side of the keel to see what is going on inside, then welded back afterwards before the outside is coated.

 

[EddBee]

I genuinely hadn't thought of bitumen- so fixated on clever clever modern solutions. Thanks.
There is a post on the junk rig association asking similar questions and one poster filled them with some kind of oil and left the breathers open to allow for expansion in hot spells, and avoiding a keel explosion. I suppose solid bitumen might also soften and rise (and would be a bugger to clean up) but it would i imagine have to be very very warm...

 

[srm]

I seem to remember an engineer advising hydraulic oil for such uses as it does not have any water content.
My old steel boat had voids in the bilge filled with bitumen and I never noticed softening, but then that was below the waterline in northern waters so low sea temperatures. If you fill the keels with oil they will normally be at sea temperature so expansion should not be a big problem. It could be more so if you haul out in the south though and one is in direct sunlight.

 

[RogerJolly]

I have just come into possession of a Kingfisher 30s, which i am- overall- very pleased with. As you might know the keels are steel with lead at the base and were (previously- since altered it seems) used as fuel tanks. After a period of neglect there is work to do on the external steel and i've found advice on here about how to tackle that, but should i be worried about the internal surfaces of the keels? As i see it this is now an open surfact of steel, maybe with some old diesel and no doubt water slopping about, potentially ripe for corrosion that would go on without me being aware of it. There's no access, so if it does need sorting it's going to be a job and a half. My thoughts are to drain and dry as best as possible, treat with rust converter if possible and (since they are meant to be ballast) fill with.. something. Epoxy and lead shot? just epoxy? some kind of anti corrosion agent? Or am I over thininking this? -this is quarter inch steel, but then the boat is nudging 50...
Thoughts?

I'd say you were overthinking.

My Kingfisher 26 was the same. I just left the diesel in, topped right up.

Eventually the seams where the bottom plate is welded to the sides started to let go and ooze water/diesel. Whether my (lack of) inside treatment contributed I don't know. This seemed a bit of a nightmare as I couldn't see how it could be welded without the lead melting and falling out, and with contamination from the oozing water/diesel. In the end I drained the diesel and sheathed the bottom few inches of keel with epoxy/glass (the curing seemed to beat the new oozing contamination after drying). Put the diesel back. Just left with a patch job every couple of years where the sheathing started to peel at the top.

Did the same job on the other keel as a preventative measure. On this one wire brushing in preparation actually started leak. Fixed with that underwater setting epoxy putting, held in place along the seam for quarter hour.

Am interested in the 'advice on here...'. Haven't noticed it. Academic interest now though as no longer own the boat.

 

[EddBee]

I'd say you were overthinking.

My Kingfisher 26 was the same. I just left the diesel in, topped right up.

Eventually the seams where the bottom plate is welded to the sides started to let go and ooze water/diesel. Whether my (lack of) inside treatment contributed I don't know. This seemed a bit of a nightmare as I couldn't see how it could be welded without the lead melting and falling out, and with contamination from the oozing water/diesel. In the end I drained the diesel and sheathed the bottom few inches of keel with epoxy/glass (the curing seemed to beat the new oozing contamination after drying). Put the diesel back. Just left with a patch job every couple of years where the sheathing started to peel at the top.

Did the same job on the other keel as a preventative measure. On this one wire brushing in preparation actually started leak. Fixed with that underwater setting epoxy putting, held in place along the seam for quarter hour.

Am interested in the 'advice on here...'. Haven't noticed it. Academic interest now though as no longer own the boat.

I didn't mention, for fear of complication, that i do have one dribbling keel- seems to be rusty water with a slight diesel tang to it. I know that the KYOA page (inactive?) has an example of some steel 'shoes' for the keel which sound like they are a response to a recognised issue. There's a youtube channel called 'the boat rambler' who has a K30 too, and seems to have the same dribble, fixed with epoxy putty in the short term.

The keels seem (still at the stage of tracing lines) to be redundant as tanks with a new(ish) S/S tank in the aft locker so it's really just a question of rendering them safe.

 

[srm]

Another technique on old steel boats was to patch small leaks on the inside with a cement mortar. Can you pour some into the keels to fill the bottoms? Perhaps drill drain holes first to get rid of old water/diesel.
Likewise, in the 70's, I came across steel water tanks on a fishing boat that were treated inside with a cement wash to prevent corrosion.

 

[EddBee]

i think i can drain them/ pump them out through the original pipes which seem to be there still- i could also fill them with -whatever- through there. I'd prefer this to drilling in, although i had thought about cutting an access hole but that's a really brutal option. I just want to make sure whatever i fill them with doesn't allow the rust to continue to do its work unseen, so something that excludes water and fills gaps would be ideal.

 

[srm]

There is usually a space in the bottom of tanks below the suction where a sludgy mess gradually builds over the years, hence my sugestion of drain hole(s) at the lowest point so that you can flush the mess out before filling/sealing. The holes could then be filled closed by welding or an epoxy putty.
I would guess that your new fuel tank was installed because the keel tanks had become contaminated and kept blocking the fuel filters.