Forums: Whisstock Designs: Lead keel alternative New Topic Post Reply
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benfarr
Posted: Apr 26th, 2016 at 04:39   |   Subject: Lead keel alternative
Hi

A lead keel is very expensive in NZ. Lead is expensive & so is forging. What alternatives are there ?
I've been reading on the internet about concrete filled with scrap metal.
OR cast iron (piece of railway track)
What do you think of these ideas ?

Obviously the concrete version would be lighter, could I increase the size of the keel or place ballast in the hull ?

I look forward to your reply.

Many thanks Ben Farr

p.s. Progress is going smooth & steady -
thanks to your great instructions
debenriver
Posted: Apr 27th, 2016 at 21:35   |   Subject: Lead keel alternative
Hi Ben

I need to do a few calculations – I'll be back to you later this evening.

I'm really glad all is going well.

Sometime, if you can, I would love to see any photos you have of the build.

Best regards

George



benfarr
Posted: Jun 28th, 2016 at 06:25   |   Subject: Lead keel alternative
What's the verdict ?
debenriver
Posted: Jun 28th, 2016 at 21:40   |   Subject: Lead keel alternative
Hi Ben

I'm really sorry – I did look at this but somehow I din't answer you.

The problem is that lead weighs 11,300 kg per m^3; cast iron weighs about 7,200 kg per m^3 and concrete 2,400 per m^3.

So concrete isn't basically very heavy (or rather it isn't very dense)

Cast Iron is a viable alternative. A cast iron keel to replace the lead keel would need to be about 185mm wide, instead of 120mm for lead, which isn't horrible. But this is for a proper foundry cast iron keel, which will probably be nearly as expensive as a lead keel.

The keel really isn't large enough to use concrete with cast iron in it and still remain structurally viable – and you wouldn't get sufficient weight within a reasonably sized keel.

Have you considered casting a lead keel yourself, using scrap lead? Many of our builders do this. There are some good pictures on the 077 web page slide show, which give a good guide to the process. Making a casting mould is not very difficult and the melting system can be quite basic as long as it can melt all the lead in one go. Scrap lead is usually fairly reasonably priced.

You can of course do something like bolt a couple of railway irons on, and then have internal ballast. But the boat will be less stable and less capable, because the vertical centre of gravity (VCG) will be higher.

You could compensate for this by making a deeper keel – so even though the material making up the keel was less dense, the total weight and VCG of the keel remained reasonably constant. The current lead keel weighs about 279kg and has the VCG at -0.268 (268mm below the dwl) and the LCG at -2371 (2371mm aft of Position 000).

But I don't think concrete is going to do the job, however you reinforce it, add steel to it etc.

You could consider using steel plate. If you have access to a reasonably-priced steel fabrication company with CNC equipment (most do have this). You could then make the keel from 7 or 8 vertical layers of profiled steel plates each 25mm thick – or perhaps better 12 layers of 15mm plate. These could be bolted or welded together. I you wanted to go this route I can supply DXF files for the CNC facility to cut the plates etc.

Steel is similar to cast iron as regards weight – but it corrodes in a marine environment more easily than cast iron, or of course lead – which is pretty much the ideal material.

Hope this helps.

I'd be happy to provide additional drawings for a cast iron keel, a steel keel, or indeed the casting box for a lead keel.

George