Fulmar Keel Corrosion/Erosion

[chrisbailey]

The Fulmar does not normally have bonding between the keel and anode. there is a conection from the mast to the keel using a wide woven earthing strap but that is for lightening protection. I dont think the problem is electrolosis more like slag as mentioned earlier in a poor casting. A good clean, repair and paint job shold solve the problem.

 

[YELLOW BOAT]

NEVER NEVER NEVER use stainless steel to repair normal steel like your keel!
You will introduce a very high galvanic element ( +/- 0.2Volts! , could burn a light bulb on it!) and when this makes contact with water your keel will riust away very fast!
To repair your keel with epoxy you must remove all paint from the keel and have it gritblasted . Epoxy does not fit with the normal coating on the keel ( unless its already epoxied) .
If you don't want to do the whole keel , just take epoxy filler and normal paint like primocon from international.
More info at the paint sites.
Ad

 

[YELLOW BOAT]

Hi Peter,
You're absolutely right about bad castings!
I believe almost all keels are bad castings to a certain degree. Also Sometimes(or even most times?) the keels were painted without removing the millscale ( ironoxide formed during casting) . That's asking for trouble.
There is a good method to get rid of it. gritblasting followed by laminating etwo thin layers of glass with epoxy or ( less dangereous for your health) vinylster resin.
Ad

 

[YELLOW BOAT]

The Fulmar does not normally have bonding between the keel and anode. there is a conection from the mast to the keel using a wide woven earthing strap but that is for lightening protection. I dont think the problem is electrolosis more like slag as mentioned earlier in a poor casting. A good clean, repair and paint job shold solve the problem.

Aha . Could be a bad lead inside the mast e.g. for the light or others.
A bad isolation can easily result in stray currents withoput tripping your fuses.
This has happend more than once especially on older yachts ( with old wiring!).
Ad

 

[Bilgediver]

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

Have you scraped around in ths damaged areas with a sharp instrument like a screw driver and if so was the material soft and easy to break away till you reached solid metal???

This looks like graphitisation which is a sort of sea water corrosion of cast iron. I had it on my Westerly chieftain keels at the lower front corner. It can be due to a number of circumstances and itt looks like your over enthusiasm with the power washer found it and dug it out

If it is a soft grey material then all you can do is dig it out to good metal and then prime the metal and fill the holes with something like west system. It is more cosmetic than structural and should not be happening in way of the studs etc.

The only disadvantage is your keel is not as heavy as it was and you get sleepless nights for a week or two.

It is possible that contaminants in the mud have accelerated the process and that it was there under the antifoul last year.

 

[charles_reed]

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

I'd guess it's certainly galvanic corrosion - whether it's "radio-active mud", strange microorganisms, casting impurities or errant currents in a marina is pretty immaterial.

I'd certainly clean it to bare metal and, before it has time to rust fill the craters with epoxy putty, coat (again on bright shiny metal) with 5-8 layers of Primocon before re-anti-fouling.

The secret is to only key onto clean, unoxidised iron - which wasn't done last time, hence the craters.

 

[30boat]

Have you scraped around in ths damaged areas with a sharp instrument like a screw driver and if so was the material soft and easy to break away till you reached solid metal???

This looks like graphitisation which is a sort of sea water corrosion of cast iron. I had it on my Westerly chieftain keels at the lower front corner. It can be due to a number of circumstances and itt looks like your over enthusiasm with the power washer found it and dug it out

If it is a soft grey material then all you can do is dig it out to good metal and then prime the metal and fill the holes with something like west system. It is more cosmetic than structural and should not be happening in way of the studs etc.

The only disadvantage is your keel is not as heavy as it was and you get sleepless nights for a week or two.

It is possible that contaminants in the mud have accelerated the process and that it was there under the antifoul last year.

I had that on the exhaust manifold of my old Bukh.It was like the iron had leeched out and only the graphite was left.

 

[Bilgediver]

I had that on the exhaust manifold of my old Bukh.It was like the iron had leeched out and only the graphite was left.

It is more usual where the sea water is heated. Ie Ships evapourators and boiler feed pumps but does happen at a slower rate in cold sea water. Maybe acidic mud helps In thin metal it is a disaster but a solid keel casting it should not be a problem so long as cleaned back to clean metal before priming and filling.

 

[YELLOW BOAT]

Just a bit background about castings.
The post about the carbon is only right if the keel is made from cast iron and not cast steel.
Its an often made confusion.
Cast Iron normally has 2-4.5 % Carbon , even more with bad castings.
Cast steel shoud have 0.2-0.5 % .
Because cast steel is more expensive keels normally will be made from cast iron.
Ad

 

[Sinc]

Thanks to all for your replies and advice.
We had a further look at it yesterday and the damage is pretty much confined to one side and the trailing edge and the inside of the craters has that 'slag' look to them so casting issues may be the problem.

We will repair along the lines suggested and see what happens over the next season.

As far as I know there is no electrical connection between the keel and the engine. I will try testing as suggested. She's qite a dry boat so not much bilge water to connect as someone suggested.

I wasn't aware of any connection from mast to keel - and can't see any. But we have had some electrical issues in the mast - neither tricolour or anchor light work at the moment - so I'd be interested to hear if there's any way of testing for stray current between the two. (please excuse the electical ignorance here). I guess a simple continuity test would show if they are connected?

Thanks again for your advice and knowledge.

 

[chrisbailey]

Mast earthing

If you look in the forward end of the port side saloon locker if your mast is earthed to the keel you will see a braided flat cable coming into the locker and attached to the forward keel bolt. From the locker it runs under the saloon floor boards and up the side of the mast post and is then attached to the bolt that holds the mast step.

 

[Sinc]

If you look in the forward end of the port side saloon locker if your mast is earthed to the keel you will see a braided flat cable coming into the locker and attached to the forward keel bolt. From the locker it runs under the saloon floor boards and up the side of the mast post and is then attached to the bolt that holds the mast step.

Thanks Chris,
Don't recall seeing anything attached to the keel bolts but I'll look next time I'm there.