Corroding ballast splitting the keel top!

[Zagato]

I have looked at a couple of boats today that have long keels. On the nicer of the two (It's VERY nice ) there is a 5" long x 2mm wide split running length ways which is visible when you lift the floorboards, and bubbling rust around the top edges where the Ballast meets the GRP. Another smaller split goes port to starboard further back.

I believe ballast in some boats is iron which will corrode and I am really trying to find out the consequences and what would be involved to cure the problem. I suppose it could be surface water corroding it but unlikely or maybe a stress crack but then why the other crack runnig the opposite way.

If the keel has been compromised maybe by running aground, then salt water would fill the keel, once that has happened it's got to be game over surely as the ballast will gradually rust and eventually split/blow the keel.

What do you think, anyone got any experiance of this matter? Thanks.

 

[Downsman]

I had a steel hull that I ballasted with fine mix concrete and window sash weights which were cast iron. I was a bit dubious about doing so but spoke to a Boffin at one of the big ready mix companies ( Francis & Co that were at Littlehampton) I was told that as long as ALL air was excluded rust would not be a problem. And so it proved over the 10 years I owned the boat, never a sign of rust, swelling, splitting etc: So perhaps in the case of the Crabbers, if you could seal those cracks completely airtight, the rust would not progress to a point where it caused problems.
That's purely a guess, no doubt someone with more scientific knowledge will put us straight.

 

[Seajet]

If the whole keel - not just the top in the bilges - is encapsulated, there's always the risk of water getting in through grounding damage, boatyard crane clumsiness ashore, etc.

Then it will 'swell' if the usual cast iron; hard to say without seeing the boat, and anything is fixable if money is thrown at it, but my instinct sadly is 'run like the wind' !

Looking at a few more similar boats should give an idea, and I'm sure more knowledgeable people will be along.

 

[boatmike]

I have indeed seen this before. Ecapsulated internal ballast in a GRP keel is fine but if not properly encapsulated can indeed corrode and expand causing problems that require major surgery to repair. You don't say where the split is but if it's in the GRP hull walk away at a brisk pace. If its in the encapsulation cap which is simply resin poured in after the ballast it's not quite as serious and may in fact only be shrinkage of the resin when first poured due to too much being poured in at once (mass effect) A photo would be useful but failing that please be more explicit regarding what is in fact split

 

[Danielmc]

A couple of years ago I quite fancied a Cornish Shrimper, but decided against it when two separate boat repairers both advised me to check the operation of the keel on any boat I looked at. The encapsulated mild steel pellets (mixed with resin and slate dust if I recall correctly) used for ballast were known to cause problems by swelling up and causing the keelbox to pinch the keel plate once water got to them and rust followed. The only solution (I was advised) was to chisel out all the original ballast and refit something less likely to corrode such as lead; a costly (and dirty) repair job. I recall being a bit surprised that such expensive (to me at least) boats had such a cheap ballast arrangement.

I ended up buying a Memory 19...

 

[Zagato]

Danielmc - that is exackly what was described to me by an authority on Crabbers. The swelling gets so bad that the keel will not lift up and down as it is pinched! I need to find out if they used the same ballast in Crabbers - probably

Boatmike - the crack is on top when you take up the floor boards, the crack is in the covering (whatever that is made of) so we don't know what is underneath!!?? BUT the outside top edges are visibly corroded so I should think it will be corrosion causing it. It needs digging out to investigate really.

If the hull has been compromised and water has got in game over unless Waxoyl or something could be poured in to inhibit the corrosion, but it would cost thousands to sort eventually and who wants a keel that could crack open at anytime.

If it is from water over flowing from the bilges so is only a small amount and maybe has not reached the bottom of the keel, then the top corrosion could be "dug" out and treated! I am being overly positive as the boat is so good

To treat corrosion you need to acid convert the rust but this will only treat surface rust, also I wonder how acid treatments would effect GRP You could pour in Dinitrol or Waxoyl but that would only inhibit the rust. Waxoyl due to its white spirit content bubbles rubber some plastics and tarmac driveways - again I would be worried how it affected GRP.

It's a shame as the NICE BOAT is really nice

I think I know the answer and that is to walk away - sadly it will probably be the end of the Crabber 24 dream

 

[Deleted member 36384]

It doesn't have tone the end of the dream. If you get the boat for a good price, its not that difficult a job to do properly. Consider it an opportunity, if you have the time and will.

 

[Zagato]

If water has got in it's a case of chopping out a complete side GRP panel to get the old ballast out, replacing the side and pouring new ballast in. Lead ballast alone could be 1-1.5K apparently It's just not financially viable...

 

[lw395]

If water has got in it's a case of chopping out a complete side GRP panel to get the old ballast out, replacing the side and pouring new ballast in. Lead ballast alone could be 1-1.5K apparently It's just not financially viable...

Depends how cheap the boat is.

 

[LittleSister]

If water has got in it's a case of chopping out a complete side GRP panel to get the old ballast out, replacing the side and pouring new ballast in. Lead ballast alone could be 1-1.5K apparently It's just not financially viable...

I am no expert on this, but I do not think the response necessarily has to be that drastic. You may need only to dry out and reseal the ballast, not remove it altogether. There are three issues.

1) First is the ingress of water which caused the problem in the first place. There is nothing wrong with iron/steel ballast or encapsulated keels, but the iron/steel ballast must be kept dry. That is not usually a problem. If it isn't kept dry (inadequate sealing, later damage or whatever) the resultant rusting expands the ballast, and MAY cause a serious problem, but not necessarily (depends on which stage it's caught, where it's expanded). So the job that MUST be done is to identify where water is getting into the ballast and stop it doing so, and to drain and dry out the ballast.

2) Whether the expanding ballast has caused damage to the hull or keel moulding which requires repair. If so this must be repaired. There's no point in doing this if you haven't dealt with one (above).

3) If the ballast has expanded enough to cause damage, do you need to remove some of the ballast in order to effect a proper repair? It may be that you just end up with a slight, non-problematic bulge somewhere. If you've repaired the hull and dealt with the original problem you can stop there. Otherwise you might need to remove some ballast, but I would have thought that would usually involve just grinding some away in the problem area, not often removing the whole lot and starting again.

Enacapsulated balllast rarely has problems. When there are problems they can be major, but are usually minor.

 

[Tranona]

Depends to an extent whether it is a casting dropped in. This is usually set in a filler and the outside moulding is normally thick enough so that it does not wear away. You need to check the bottom of the keel to see if there is any damage that might have let water in from there. Having a centreboard slot does not help as the damage maybe in the slot. The casting is glassed over to form the bilge, so it could be that this has failed and the water has got in from the top. Rust goes a long way - like blood and the damage may be localised. Severe damage would show by external cracks in the moulding as the rust expands.

The alternative form of ballast, metal or shot set in resin is potentially more of a problem because there is more surface area to go rusty if water does get in. I built a SeaWych in the 70's with this form of ballast and aa subsequent owner allowed the keel shoes to wear away as it dried on a hard bottom. The rust split the bottom of the keel. The guy who bought it chipped all the old ballast out, moulded a new keel and reballasted. Fortunately I still had the original instructions on how to do it. Lot of work, but AFAIK the boat is still in use.

So, find out what the ballast actually is. If as seems likely it is water got in from the top, it is not difficult to repair. If it was seriously rusted you would see more than cracks and stains. Probably not a DIY job and not one you would choose to buy without knowing exactly what needs doing.

 

[Colvic Watson]

A one time exposure to air or water has no long lasting damage, once that oxygen is used up, the rusting metal doesn't make more of it, so the rust process halts. What can be damaging is continuous exposure to a source of oxygen. Walk around any number of boatyards and try and find a yacht with bulging or cracked GRP; cases do exist but they are rare. For example, there has only been one reported case in all the Colvic Watson fleet of 100's of yachts - and that was caused by a very amateur seal on the ballast. The new owner cutout the ballast and replaced with lead.

 

[Zagato]

Well having contacted a few Crabber 24 owners last night and even speaking to "Mr Crabber" Peter Thomas, it appears splits and corrosion around the edge is not uncommon on the old Crabber24's, 22's etc. and it is nothing to worry about. Splits can occur from new from shrinkage of the resin when cooling as suggested hear earlier. Some of the owners have said their splits have not changed in over ten years i.e. caused by shrinkage not corrosion.

This is a statement made by Peter Thomas some time ago...

"Dear all.
An interesting subject.
The ballast in the Cornish Crabbers is a combination of steel punchings (little disks of steel) resin and slate powder. The slate powder eliminates the danger of exo-therming when mixing large amounts of resin at once.
There are always chances of this resin / ballast mix expanding and contracting which can cause some cracks in the system. If these are spotted then it would be good to dry them out and fill them to make them waterproof. However the steel punchings are well mixed and should be well sealed from each other in most cases.

From my experience there have been a few Shrimpers that have had problems with ballast expansion. These boats tend to be wetter than the bigger boats in the range and the reason we hear about these is that there are 1100 of them in existence..... The tell tale for this quite rare problem on a Shrimper is that the center plate gets stuck due to the ballast expanding and closing the plate case.
This is certainly not an epidemic problem and a common sense approach is all that is required.
On the Crabber 26 we use lead ballast which is cast in 3 lumps. This makes the boat very stable and enables us to get better headroom etc...... BUT it costs 4 times what the steel ballast would cost.....
Don't let this take your mind off your sailing. Peter Thomas"

So I slept well last night having spoken to Peter who put my mind at ease (A very helpful and accommodating chap having spent half the day with me on his day off whilst also having to reassure a panicky buyer over the phone late last night! )