Rust on Bilge Keels

[Dougie_the_Mate]

Earlier in the year we had everything below the waterline cleaned . It was professionally done and 2 coats of primer were applied to her hull and the keels with 2 coats of Anti fouling added. We were very pleased with how she looked after the job - which wasn't cheap.

W
Yesterday we were fitting her out prior to launching next week, and i noticed some spots of rust on the starboard keel. I contacted the firm who did the job and asked was this not a bit soon to be seeing rust, since it was earlier this year the job was done. They replied that it had been out of the water since October and the primer was only effective for so long and in any case they had a similar job and the spots were 'surface rust'.

I wondered what folks thoughts might be as to whether or not my expectation that it would be clean for a wee while longer, is unreasonable and if anyone has heard of 'surface rust'?

 

[VicS]

How were the keels prepared?

• Grit blasted to Swedish Standard SA2½ ?
• Tested for chlorjde (and other soluble iron salts) with potassium hexacyanoferrate(III) paper ?
• Primed before any surface rust could form?

You expectations were probably too high.

Vyv Cox will be along soon.

 

[john_morris_uk]

I had our keel blasted and then coated with six or seven coats of epoxy. I still have to attend to the odd patch of rust..

Two coats sounds a bit thin.

 

[Elessar]

Earlier in the year we had everything below the waterline cleaned . It was professionally done and 2 coats of primer were applied to her hull and the keels with 2 coats of Anti fouling added. We were very pleased with how she looked after the job - which wasn't cheap.

W
Yesterday we were fitting her out prior to launching next week, and i noticed some spots of rust on the starboard keel. I contacted the firm who did the job and asked was this not a bit soon to be seeing rust, since it was earlier this year the job was done. They replied that it had been out of the water since October and the primer was only effective for so long and in any case they had a similar job and the spots were 'surface rust'.

I wondered what folks thoughts might be as to whether or not my expectation that it would be clean for a wee while longer, is unreasonable and if anyone has heard of 'surface rust'?

If you want to minimise rust you need to take the keels off the boat for a start or you can’t blast the top of them.

Even then, keels are often made of terrible, porous metal.

Blast, and then epoxy is your best bet and it may stay fairly rust free for ages. But I don’t know anyone who will guarantee no rust on an iron keel. Because it’s impossible to guarantee.

 

[Elessar]

I had our keel blasted and then coated with six or seven coats of epoxy. I still have to attend to the odd patch of rust..

Two coats sounds a bit thin.

“Epoxy” doesn’t say much John. Solvented or solvent free? Dry film thickness of 2 coats of solvent free can be about the same as 7 solvented.

Having said that I agree with the premise the thicker is better but even so keels can be porous so short of baking them in an oven you’re fighting a battle.

Westerly keels seem particularly poor, with one side worse than the other - I was told that this is because they were cast on their side and the materials were rather variable. Anyone know if this is true?

 

[Sea-Fever]

I’m wondering how much rust you would have to have to make a keel weighing several hundreds of kg become less effective? And with that in mind I’m not convinced it’s worth thinking about IMHO.

 

[Elessar]

I’m wondering how much rust you would have to have to make a keel weighing several hundreds of kg become less effective? And with that in mind I’m not convinced it’s worth thinking about IMHO.

That’s a good attitude. It isn’t going to fall off unless the bolts are compromised.
The rusty bits do foul though.

 

[Derek ide]

That’s a good attitude. It isn’t going to fall off unless the bolts are compromised.
The rusty bits do foul though.

My Westerly Fulmar keel used to show more rusting when out of the water in the winter than when in commission., once afloat the rusting was minimal. Wire brush or grind the patches then primacon and antifoul. Once immersed the rusting slows down, starved of oxygen?

 

[Elessar]

My Westerly Fulmar keel used to show more rusting when out of the water in the winter than when in commission., once afloat the rusting was minimal. Wire brush or grind the patches then primacon and antifoul. Once immersed the rusting slows down, starved of oxygen?

We need Vyv to explain that!

 

[vyv_cox]

We need Vyv to explain that!

I think I would need more detail before commenting. There is plenty of dissolved oxygen in seawater, certainly enough to rust our keels.

One point arising, as mentioned in the thread, the cast iron used for many keels is pretty poor stuff, especially in the horizontal sand cast keels on many boats (Westerly, Sadler, amongst others). Wire brushing tends to drive rust into the porosity and graphite. Needle gunning is great on steel but even worse than wire brushing on iron. Grit blasting is always going to be best but angle grinding is not too bad.

 

[ghostlymoron]

Doesn't angle grinding leave marks?
I never bother too much about rust patches on keels and accept some patches will need doing every year - I just wire brush the patches, 2 coats of Primocon and anti foul. Out of sight out of mind.