From winged keel to bulb keel

Discussion in 'Sailboats' started by Mad for sail, Nov 15, 2011.

  1. Mad for sail
    Joined: Nov 2011
    Posts: 53
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    Location: Brazil

    Mad for sail Junior Member

    Hello Mikko, it´s been a while!

    All models have 1:20 scale and the longest keel prototype is about 12,5 cm.
    The process used to produce the parts generates a extremely precise solid based on IGES models out of ABS resins. At the end you have a model whitihn 0,1 mm precision with a hard material that you can rework with sandpaper or even cover with metalic layers like nickel or chrom.
    The machine lays very thin philaments in a cross pattern to generate the layers in a very time consuming process. Prices are tied up to the manufacturing time so a good way to reduce the cost on bigger parts is to generate hollow models. For those keel I spent between Euro 50-100.
    There are other cheper process like sthereolithography (SLA) where parts are produced by lasering a resin over a miving table. The laser beam solidifies the liquid resin generating thin layers as the table moves on vertical direction. The only problems is that the resin is poliurethan based and do not stands mechanical efforts and is highly affected by water. For bigger size prototypes a combination of SLA and a hollow model will certainly makes it cheaper.
    Once you have the models you can make a silicon mold and pour low melting point metal like lead and its alloys as silicon stands up to 250ºC without problems.
    In the picture attached you see the wing keel prototype I poured using a Pb/Sn alloy with density very close to steel. It can be handy if you really want to reproduce most of the phisical material caracteristics in your model.
    I will make a lead model of the proposed L Keel but therefore I will need to sacrifice the weights from my diving belt ....
     

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  2. Mad for sail
    Joined: Nov 2011
    Posts: 53
    Likes: 2, Points: 0, Legacy Rep: 42
    Location: Brazil

    Mad for sail Junior Member

    I was about to decide for my L-keel or so called bulb integrated keel when somebady advised to buy some books. So the outcome is that I have some new doubt´s!
    Does anybody dares to tell me the performance difference I should expect from the 3 different proposals in the picture?
     

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  3. Petros
    Joined: Oct 2007
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    Location: Arlington, WA-USA

    Petros Senior Member

    I have not followed this thread from the beginning so I do not know what else has influenced you. Presuming these keels are the same weight, keel C would put more weight lower and would give you more righting moment, from my years working in aerodyamics, both keel B and C would not be as efficient since span wise flow will be upward toward hull. Also, keel B would be slightly destabilizing directionally (not a big issue if your rudder is adequate), this means it will be less directionally stable, but will also make turns faster.

    I think keel A would be most efficient and would affect handling behavior the least and be most predicable.
     
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