Replacing an iron keel with a lead keel.

hi!

I am starting to renovate an old sailing yacht from 1908, and it has a
badly rusted iron keel. I am considering replacing the keel with a lead
one, of the same dimensions... i know it might sound ill prepared to
ask such questions but, what are the things that this would affect
if I just replaced it with a lead keel of exactly the same dimensions
and shape.

Yes, the weight of the keel will increase by 1.5 times, but what does
that change in terms of the maritime properties of the boat?

Is this a bad idea?

Thanks

-Mohan

 

It will:
- increase draft
- decrease freeboard
- possibly overstress the ballast keel support structure (keel, keelson, floors, etc.)
- cause the boat to have a shorter roll period, which may be uncomfortable
- cause the boat to have a shorter roll period, which may cause undue stress in the mast & rig
- increase rigging loads

Other than that, not much effect.

I would suggest that you stay with the existing mass and CG of ballast keel, and fit deadwoods in the existing ballast keel cavity to compensate for the smaller physical size of the lead ballast keel. Unless, of course, there is substantial internal ballast as well, the mass of which can be transfered to the new external ballast.

 

Or just cast one with a void in it to match the CG and weight of the old one.

 

Lets see, you have a one hundred or so year old sailing yacht and want to butcher the thing with a major structural change. Mike is quite correct, the same volume filled with lead will likely break the boat, as the structure will have to support near twice the weight in ballast, not to mention the rig strains with the lowered CG.

You need consult with a NA as this engineering isn't difficult, but must be done correctly, or you will break her back, certainly the rig. Personally I'd be trying as hard as possible to bring this old girl back into good form, not redesign something that was suited well enough to survive a century. Lead ballast would make a reasonable addition, but do it right, she deserves this at least for her next century.

 

What do you consider badly rusted? It may just be cosmetic.