Fulmar Keel Corrosion/Erosion

[Sinc]

Could I once again call on the experience of those who have been boat owners for many more years than I.

When we lifted our Fulmar out last week we found that the keel was showing quite serious corrosion damage. This appears to be more like electrical erosion than rust - but I could be completely wrong on this. I have posted some 'before and after' pics here:
http://tinyurl.com/6zdru4e

We bought her a year ago when she was out of the water and there were no significant corrosion problems to see either by us or the surveyor although parts of the keel had been overpainted and so could have covered repairs.

She has a hull pear anode which was about 30% worn last year so remained. The shaft anode was replaced but has disappeared over the season. Shaft and prop are unmarked and the hull anode is further eroded but still about 50+% remaining.

For the last season she has been sitting in soft mud every low tide alongside a shore pontoon on the Itchen. There is no shore power connection.

We have two problems to resolve:
1 - Establish the cause so we can prevent recurrence over the next seasons
2 - Decide how best to repair the damage

Any ideas would be much appreciated.

Thanks in advance, Graham

 

[Tranona]

Highly unlikely to be anything to do with galvanic action. Looks just like ordinary rust. Cast iron has a lot of impurities in it and it is difficult to get a good key for a protective coating. Only solution is to have it blasted and immediately epoxy coated. No mean undertaking and you may decide to live with it and just clean up and repaint every year.

Suggest you speak to a blasting contractor such as Symblast for advice and a quote.

 

[30boat]

I confess my ignorance of all things electrical but that looks like galvanic corrosion.Where do you keep her?Marinas many times have serious stray currents.A friend once lost his prop after having to replace the anodes roughly every month for a while.Do you have anything connected to the keel bolts?

 

[vyv_cox]

That is very strange damage, the like of which I have not seen before. I note that the internal surface of the big pits is grey, not red. Is this as it was hauled out or have you cleaned it up and treated it? It doesn't really look like corrosion damage to me, could it be porosity in the iron that has been filled before you bought the boat? One clue might be if the damage is all on one side. Keels are cast lying down, so gas bubbles would float to the top.

 

[30boat]

That is very strange damage, the like of which I have not seen before. I note that the internal surface of the big pits is grey, not red. Is this as it was hauled out or have you cleaned it up and treated it? It doesn't really look like corrosion damage to me, could it be porosity in the iron that has been filled before you bought the boat? One clue might be if the damage is all on one side. Keels are cast lying down, so gas bubbles would float to the top.

Actually I remember a friend's "82 Jeanneau that had holes just like that that were full of casting impurities.I cleaned and epoxy filled them and the problem never returned.

 

[Sinc]

That is very strange damage, the like of which I have not seen before. I note that the internal surface of the big pits is grey, not red. Is this as it was hauled out or have you cleaned it up and treated it? It doesn't really look like corrosion damage to me, could it be porosity in the iron that has been filled before you bought the boat? One clue might be if the damage is all on one side. Keels are cast lying down, so gas bubbles would float to the top.

These pics were taken and hour after coming out of the water. Nothing done at all apart from a jet wash.
It certainly doesn't look like normal rust damage to me - hence the thought of electroysis.
From recollection, most of the damage is on one side - but I'd need to check that.
To put it in perspective, those big pits are maybe 20mm dia. and 10mm deep and there is also some damage to the trailing edge of the fin. Not easily seen in the photos - I never competed with David Bailey!
Could the mud immersion have anything to do with it do you think?

 

[Tranona]

I have had pits like that on my iron keel, particularly at the top and on the mating face with the hull. my keel is an old fashioned trough shape that was cast upright so all the impurities went to the top. 20 years ago I cleaned them all out and levelled the ones on the face with epoxy. Still reasonable with the odd breakout of rust at the edges. Just last year had it blasted by Symblast and a holding coat put on as the boat is laid up.

Suspect the Fulmar keel has been filled in the past, but no protective coating.

 

[Sinc]

I have had pits like that on my iron keel, particularly at the top and on the mating face with the hull. my keel is an old fashioned trough shape that was cast upright so all the impurities went to the top. 20 years ago I cleaned them all out and levelled the ones on the face with epoxy. Still reasonable with the odd breakout of rust at the edges. Just last year had it blasted by Symblast and a holding coat put on as the boat is laid up.

Suspect the Fulmar keel has been filled in the past, but no protective coating.

Thanks Tranona.
I'm beginning to feel a bit better about this. I guess what I was really concerned about was some electical issue that we would have real trouble finding a solution for.

So far the majority view is against gavanic erosion.

 

[chrisbailey]

rusty keels can be treated

I had a similar problem with one of the keels on my fulmar quite a few years ago. I have had the boat since new in 1986 so I knew the history. I believe that some of the keels were poor quality castings, hence the type of damage you have.
I ground out the worst of the rust then treated the area with a rust converter, filled the holes with underwater epoxy putty. Then after cleaning the keels back to bare metal I painted them with 7 or 8 coats of Primocom which has lasted well over about ten years.
I don't think that is something to worry about too much as it is easily treated.

 

[30boat]

I should have added that my own Fulmar had some pits on the keel (smaller than yours)that I ground clean and filled with epoxy putty with very good results so far.

 

[richardbrennan]

I would concur with the view that it is almost certainly casting impurities especially if it is mainly on one side. Westerlys are rather famous for this and a trip round any boat yard will confirm this; very few if any will have rust free keels. Treatment depends very much on how much time and money you wish to spend.

 

[vyv_cox]

I've been thinking a little more about this overnight. Note how the silver/grey appearance inside the cavities is not corroded, whereas areas around them are red rusty. I suspect that the grey is slag that is both conducting and more noble than the iron of the keel. Perfect recipe for galvanic corrosion. Areas around the cavities are thus sacrificial and corrode to hydrated iron oxide.

I suggest that the cavities need to be completely cleaned out, almost certainly by grit blasting as I can't think of another way. Then epoxy prime, five coats normally recommended, and fill the holes with epoxy filler.

Of course it could be argued that the rusting is not normally visible and it will take a long time before a keel rusts away, so don't do anything. Just depends on attitudes, I guess.

 

[YELLOW BOAT]

Hi,
Question: is there an electric connection betwee keel/keelbolts and enghinemass or negative lead. If so , cut it because then its possibly electric. If there aint then it definetely cannot be electric corrosion.
To be shure , measure the resistance between mass and keelbolte. Should be
close to infinite.
eElectric or galvanic corrosion can only occur if there is a connection for the current to flow.
In case of electric this current can be quite high if galvanic its a very low current.
This is why a protection anode always needs a connection to the materials to be peotected.
Ad

 

[VicS]

A hull anode has been mentioned.

Is it located reasonably close to the keel?

Is it intended to protect the keel ... is it bonded to the keel?

Anything else bonded to the keel ... no bronze seacocks ?

No changes in the electrical system or possibility of a fault that could case electrolysis ( as distinct from galvanic corrosion) I'm just thinking out loud of the possibility of a stray positive connection to the keel with a return path via the prop and shaft.

 

[savageseadog]

I've been thinking a little more about this overnight. Note how the silver/grey appearance inside the cavities is not corroded, whereas areas around them are red rusty. I suspect that the grey is slag that is both conducting and more noble than the iron of the keel. Perfect recipe for galvanic corrosion. Areas around the cavities are thus sacrificial and corrode to hydrated iron oxide.

I suggest that the cavities need to be completely cleaned out, almost certainly by grit blasting as I can't think of another way. Then epoxy prime, five coats normally recommended, and fill the holes with epoxy filler.

Of course it could be argued that the rusting is not normally visible and it will take a long time before a keel rusts away, so don't do anything. Just depends on attitudes, I guess.

Just a thought. I've welded up (non marine) cast iron with specialist and stainless steel rods. Would it be possible to fill them effectively that way?

 

[YELLOW BOAT]

Normally there is no need for keelanodes on a polyester boat.
For galvanic as well as for electric corrosion there must be a connection somewhere at the keel with mass ( electric) or shaft and prop ( galvanic).
For the last the distance between shaft/prop and keel probably is too big for a problem.
Anodes cannot protect against electric corrosion e.g. by stray currents,
The anodes would be eaten in months!
Better start measuring . that's also what an expert probably would start with.
By the way , also a very dirty bilge can conduct a stray current to the keel e.g. from a bad electric lead somewhere in the muck.Than jsut clean up thouroughly.
Ad

 

[savageseadog]

I've been thinking a little more about this overnight. Note how the silver/grey appearance inside the cavities is not corroded, whereas areas around them are red rusty. I suspect that the grey is slag that is both conducting and more noble than the iron of the keel. Perfect recipe for galvanic corrosion. Areas around the cavities are thus sacrificial and corrode to hydrated iron oxide.

I suggest that the cavities need to be completely cleaned out, almost certainly by grit blasting as I can't think of another way. Then epoxy prime, five coats normally recommended, and fill the holes with epoxy filler.

Of course it could be argued that the rusting is not normally visible and it will take a long time before a keel rusts away, so don't do anything. Just depends on attitudes, I guess.

Just a thought. I've welded up (non marine) cast iron with specialist and stainless steel rods. Would it be possible to fill them effectively that way?

 

[Robin]

As mentioned before Westerly keels were not the best but they are never going to corrode enough to be more than a cosmetic problem. We took our W33 keel when we had it back to bare metal (scraped, chipped and ground,not blasted), then treated it immediately with a liquid rust killer before painting it with 6 or more coats of International Primocon. Subsequent years we just sanded off any bubbles and touched them up with Primocon before antifouing and this worked for the rest of the time we had that boat, another 13 years.

If you have it blasted then it needs to be coated within minutes of that finishing to be really effective, not easy to arrange nor the weather to time in with it.

Epoxy coatings IMO are not really conducive to doing the job in the yard in winter and anyway work their best on better quality castings. Our Jeanneau keel on the last boat was a much better finish and apart from touching in the odd spot with Primocon needed nothing else over the ten years we had her.

Beware painting keels after a cold spell BTW, because they hold the cold and are a magnet for moisture collection with a damp airflow. I have seen paint fall off in slabs because it hadn't stuck to the keel or the coating on it because of this.

 

[Seajet]

Is the boat anywhere like the Chichester - Portsmouth area ?

There is a known problem with 'accelerated corrosion' around there.

My boat's 3/4" galvanised mild steel keel plate suffered terminal corrosion after about 25 years, the majority of which included good maintenance during the winters, with pitting similar to that shown; the replacement started to go the same way, until I fitted an anode.

There are no electrical items anywhere near the keel inside or out and the anode was fitted on a hunch, but seeing as the corrosion has stopped and the anode is fizzing away to disappearing it seems to work !

I happen to believe in the 'stray electrical current' theory; there's a marina and the mains electrical supply to Hayling Island close by...

I had a chat with Portsmouth University Marine Metallurgy Dept, they were keen to see my boat; as I say there is a known problem with accelerated corrosion in the area.

They were mainly focussed on a type of microrganism with excretes metal-corroding stuff.

It proved not to be the case on my boat, but as this is known to be in the area it's worth bearing in mind; not sure how far spread the 'steel eating microbes' are !

 

[PeterGibbs]

I had a similar problem with one of the keels on my fulmar quite a few years ago. I have had the boat since new in 1986 so I knew the history. I believe that some of the keels were poor quality castings, hence the type of damage you have.
I ground out the worst of the rust then treated the area with a rust converter, filled the holes with underwater epoxy putty. Then after cleaning the keels back to bare metal I painted them with 7 or 8 coats of Primocom which has lasted well over about ten years.
I don't think that is something to worry about too much as it is easily treated.

Stray currents should always be considered but in this case, where only the keel is affected, I think your problem lies closer to home.

A generation ago (Fulmar age) keels were not poured to the standards expected today - they were regarded as lumps that kept the boat upright. I recall over the 9 years I had a Fulmar having to spend time most years making good on the keels. I suspect if you follow the well-intentioned advice above and have the keel blasted and painted, in two seasons time you will be wondering why you went to the expense.

Patch, paint and sail on - she's a great boat and you should not lose a moment's confidence in her design.

PWG