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Thread: weight of cast iron vs. lead for new keel

  1. #1
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    wondering if anyone has pertinent experience replacing missing cast iron keel w/ new lead one??? 33' william hand motorsailor in need of one. lead is currently .53/pound to be poured into your mold, bloomfield's in providence. appears to be the way to go with this project, unless we find the old one. thanks.

  2. #2
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    Do you have the drawings? Seems like it wouldn't be too hard to modify the size of the ballast keel based upon the greater weight/unit volume of lead vs iron.

    The actual attachment would likely be different as many iron keels have pockets a bit down from their upper surface for access to the nuts for the keel bolts. Lead usually uses a different technique.

    I had, in one of my more demented moments, the same idea with Phoenix; maybe we can strike a deal, LOL.

  3. #3

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    My vote would be for lead. Vastly fewer corrosion problems and enhanced performance.

    A lead keel of the same size would give much more righting moment. A lead keel of the same weight would give shallower draft and less drag.

  4. #4
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    I wouldn't be too to quick to replace iron with lead. You could actually end up with LESS righting moment. Yes I know that iron is about 475 lbs/cu ft, and lead is 710.

    Having got your attention, let me explain. I don't know the shape or weight of the keel. If the iron keel is replace with a lead one of the same size and shape it will be heavier and the righting moment will be greater. But, do we really want to add that much displacement to the boat?

    On the other hand if the lead keel is simply reduced in depth to make it the same weight as the iron, then the distance from center of buoyancy to the center of gravity of the lead keel of same weight will be less than to the CG of the iron keel.

    To make everything come out the same one needs to redesign the cross section for lead.

    Art

  5. #5
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    Or keep the profile and sections the same w/ the lead at the lowest point & filling the unused space above it w/ more deadwood or empty sump - same displacement, same draft, lower cg/greater righting moment.

  6. #6

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    Good reply from AHP. He raised some important issues.

    You did not mention present performance. Would you want a stiffer boat with a light air performance penelaty?

    Could you tolarate deeper draft? That could make a stiffer boat with a slimmer keel with less drag and the same weight or even less weight and less displacement.

    If you are going to re-design and cast a keel, while you are at it you might even cast in a fin like the cup racers.

    jim

  7. #7
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    I poured and refit a lead ballast on to SAFARI to replace the cast one (long story), without changing the overall dimensions or weight as TomRobb had suggested. So far , so good and it's been 5 years. Plus it is no to bad to work with.
    mariner

  8. #8
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    Yachtdoc's "performance considerations" sound like a crock of **** to me...

    Look, if you put your ballast down lower, which you can do to some extent because lead weighs more than iron, you will improve the stability by lowering the metacentric height. It probably won't make a measureable difference in the performance of your boat. Certainly, if you seriously consider "adding fins" to your ballast keel, you ought to have your head examined. If you replace the iron keel with lead, you will have to recalculate the SHAPE and SIZE of the ballast keel to develop the dimensions of a mold which will fit the boat and maintain the balance. Just cutting some off the top of the iron ballast casting will not work, since the shape is not perfectly rectangular. Pay a naval architect what they are worth to do the calculations for you. You don't want your boat nose up and ass down on account of doing it yourself. BTW, there isn't much, if any difference, corrosion-wise between iron and lead. An iron ballast keel will rust, but so what? It does not affect its effectiveness. You can (and should) use bronze keel bolts with a lead ballast keel and iron bolts with iron ballast. The bronze stands up better, of course, but given your circumstances, were you to put in new iron keel bolts, they would certainly last longer than the rest of the boat will. Check out the forum search engine and you will find a lot of information on this issue in past posts.

  9. #9
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    Boy, I must have been OTR yesterday... LOL Sorry, doc... Still, if you get your ballast lower, your boat should be stiffer. BUT, it won't do to just cast lead instead of iron. The weight of lead is far greater than iron and you have to design the casting so the fore and aft center of balance remains the same if you switch from iron to lead.

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