Lead vs. Wood Keel

Discussion in 'Wooden Boat Building and Restoration' started by fascia, Jan 2, 2009.

  1. fascia
    Joined: Dec 2008
    Posts: 1
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    Location: Safety Harbor, Florida

    fascia Richard

    I am looking to build a wooden 16' centerboard sloop. Of the two designs I am researching, one has a wood keel and the other a 583# lead ballast keel (combined with centerboard).
    Question- what are the pros and cons of each design as far as speed, handling, safety, etc. and which would you want? Thank you for any and all comments.
     
  2. PAR
    Joined: Nov 2003
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    Location: Eustis, FL

    PAR Yacht Designer/Builder

    As in most thing about yacht design, each has good and bad things going for it.

    A wooden deadwood assembly is relatively easy to shape and cut a rabbit into. The materials are easy to find and most have tools to work it. On the other hand, wood can rot, there are more pieces to assemble, which requires more fasteners, adhesives, etc. It also can move or work as fasteners get loose, which threatens other elements of the yacht, like garboards, floor timbers, etc.

    A cast keel, typically is a shallow hunk of iron or lead that serves as the rabbit for part of the underwater areas. The advantage are: there aren't additional pieces, it's not going to rot, it absorbs damage very well and the rabbit can be cast into it. The disadvantages are: making a fairly large lead pour isn't pleasant work, in fact it's dangerous. You have to build a stout mold, acquire or make a boiler, etc. Then you have to machine the lead to clean up or cut a rabbit, bore holes for bolts, etc. Most don't know how to do this, nor have the tools for working it or manhandling it around during the process. When I met my woman, she wondered aloud, why I had a well stained cast iron bath tub in the side yard, stacked on concrete blocks, "was it a planter?". "No sweetie, it a lead casting crucible . . ." which quickly shut her up.

    From a structural stand point a cast keel is desirable, as it's one piece, isn't likely to move, swell up, check or any of the things a wooden assembly might do. The rigid nature of this casting can make a lighter boat, improving it's ballast/displacement ratio some what.

    Conversely, a cast keel will lock down the garboard and floor fastenings, which can be problematic, as the wood will naturally wet/dry cycle with moisture content. If the fasteners are wood to wood, then it's not and issue, but wood to metal, then something has to give, which is usually the wood surrounding the fastener, potentially leading to leaks. Then there's the dissimilar metals thingie that can rear up it's ugly head.

    L.F. Herreshoff commonly used lead keels in place of deadwood assemblies, with good success. His engineering skills were high compared to others of his era, which could account for much of this.

    In short, much depends on how the casting is arranged within the yacht, attachments, loading, strain transmission, etc.

    On a small boat, I'd elect not to have the complication of a cast keel, preferring to have a "shoe" or internal ballast. These can be removed or adjusted to suit loading and trim requirements, which is a plentiful issue in craft under 20', particularly if short term cruising is desired. With a fixed ballast, you haven't this "lightening ship" option.

    As far as "speed, handling and safety" the casting will provide a very slight performance increase (read a fraction of a knot) and slightly more stability. Speed would be basically the same for either version, handling would be the same for all essential purposes and safety might be improved, with a single degree or two of initial stability and the potential for a half a dozen more, at the other end of the stability curve. In other words, no significant differences in speed, handling or safety, from one to the other (assuming it's designed right).

    Which designs are you looking into?
     
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