Restoration and concrete in the bilge?!

[joliette]

I've been looking at a possible project - a gaff cutter, built in the 1920's - which was built with concrete in the bilge to about the 2nd / 3 rd plank up from the garboard. She also has a long external iron ballast keel.

External examination of the planking in this area has revealed a few soft spots, which appear to be the result of electrolisis around fastenings into the frames. The keel does not have any signs of rust runs from keel bolts.

However, it is not possible to withdraw any keel bolts or examine the frames where they are set in the concrete, although they mostly look sound where they enter the concrete.

Does anybody have any experience of this kind of issue? Would it be possible to dig the concrete out without destroying everything around it?! And, at what point would this be recommended?

 

[jon]

I have friends that had to replace the keel on a Bristol Chanel Pilot Cutter, before it fell off. It had been 'restored' before they purchased it, but the keel had not been replaced, short sited, cost cutting,respected boat builder,no names!
They had to dig out the concrete, and lead and iron ballast, with a Kango hammer to get at the keel bolts. It was a huge and very unpleasant job, so my advice would be to think very carefully before undertaking such a job.
In my opinion it is a poor way of ballasting a boat!

 

[Transcur]

If you have a ballast keel you should check and change keel bolts fairly regularly. The condition of the wood under the concrete depends on several factors. Was it put in when the boat was built. If put in from new then it is more likley to be good beneath it.What preparation was done before the concrete went in. What dissimilar metals are in close proximity. Are the frames grown or steamed ribs. It would be a real concern if you can not find the bolt heads inside the boat. This may suggest that the concrete was not put in when she was built. Concrete removal can be very time consuming, but it is really possible. The simplest way is to remove the garboards first then keep working at the edges. Thumping about in the bottom of the boat can upset things. You need to allow the rubbish to fall clear.

Be prepared for the worst . Then it can only get better. I removed the concrete from my bilges by drilling fairly large holes with a masonary bit then thumping it with a lump hammer and cold chisel, driving the concrete through the bottom. The oak wood floors and hog exposed was still white after 111 years. It turned black in about 20 minutes on exposure to air. The rest of the boat was rotten.

 

[Mirelle]

Some good advice here already.

As Pete rightly says, it's very unusual for a boat that was cemented from new to have the keel bolts buried in cement.

I'm lucky in that I know when my boat's bilges were flushed out with cement, and why, and I know the man who did it, forty years ago. We have chipped out some areas and replaced them, mainly to extract a rotten mast step and associated frame ends. I reckon that if a frame is good where it enters the cement, its probably good all the way down, but if its waffy above the cement it will be waffy below it.

I have found that a long thin cold chisel and a lump hammer does quite well - much better than a short fat cold chisel.

 

[DoubleEnder]

Best to assume that the concrete has to go, its the only way you will get any paece of mind. Otherwise you'll always wonder, as you fall off a wave . . . .

IMHO the best way to remove it is to take off garboard, and perhaps the next plank or 2 and work upwards. Horrible job, use a small kango with extreme caution. But by going in from the bottom you can avoid hammering too hard into the structure and bashing the floors, frame ends, backbone scarfs etc unneccessarily

 

[joliette]

Thank you all for the excellent advice. I hadn't thought about taking the garboard off, to avoid potential damage. Eitherway it looks like a hell of a job! I now have to decide if the boat is worth going for, and at what price. Incidentally, she's an Itchen Ferry. These have a very narrow keel - only about 3 - 4 inches wide - so they need internal ballast as you just can't get enough ballast on the outside. So, she would have been built from new with a mix of concrete and scrap iron chucked into the bilge....no doubt seemed like good idea at the time, as no one ever thought that she'd last 80 years and that someone would be interested in keeping her going!

 

[cliffordpope]

The state of the keel bolts seems the real issue. If the bolts are buried under the concrete that sounds like a potential disaster, but if you can see them emerging then they should be no more difficult to extract than any other (!)
The trouble with concrete is that you just never know. There are stories of very old boats being broken up and the bit under the concrete being the best (only) part to survive unrotted. But maybe the others sank before thay got to that age.
If you took the garboards off in preparation, perhaps the state of the floors etc then exposed would give you more confidence that the hidden wood was sound? One option might be then simply to replace them but leave the concrete?
But I don't think I could ever really be happy leaving it.