Difference between centerboard and fin keel

Discussion in 'Boat Design' started by Minthihakyaw, May 6, 2015.

  1. Minthihakyaw
    Joined: Apr 2015
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    Minthihakyaw Junior Member

    I want to know about centreboard and fin keel. I want to know which type of keel is the best for over 30m sailing yacht. I m still novice in this field. Plz guide me.
    With best wishes.:)
  2. daiquiri
    Joined: May 2004
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    Location: Italy (Garda Lake) and Croatia (Istria)

    daiquiri Engineering and Design

    When a centerboard is fully extended, there is no hydrodynamic difference between the two, everything else being equal.
    But it is hard to get everything else equal. :)

    • A centreboard will allow the boat to engage shallower waters, and will create less drag when broad reaching and running. If you are unsure about what these terms mean, you can consult this chart: http://www.rya.org.uk/SiteCollectionImages/email/inbrief14/Points-of-sail-lrg.jpg
    • A centreboard will give a smaller righting moment, because you cannot mount a bulb on it. So you either need to make it longer than a fin keel, or you have to live with the consequences of increased heel in seaway.
    • A centreboard will occupy a precious cabin space, although on a 30-m boat it can be less important than on a 10-m boat.
    • A centreboard on a boat of that size will require a powered retracting and locking mechanism, hence more things to break and fail.
    • A centreboard can get stuck inside the trunk, both because of the marine growth and because of elastic deformations of the hull in seaway.
    • A centreboard requires higher maintenance efforts than a fin keel.

    As a sum of all the above points, a centreboard will cost a lots more than a fin keel.

    On the other hand:

    • A fin keel doesn't steal space from the useful internal volume of the hull, and is of a much simpler construction.
    • A fin keel doesn't require all the mechanical maintenance the centreboard does.
    • A fin keel can carry a lead bulb, thus allowing less draft than a fully extended centreboard. However, form the hydrodynamic point of view, this configuration makes a low-AR keel (AR =Aspect Ratio), which is less performant than a high-AR one.
    • A fin keel's draft is fixed and hence a fin-keeled boat cannot engage shallow waters which a boat with the centreboard can.

    That said, for a 30-m yacht I would try to avoid the use of the centreboard because of the space requirements, because it requires a considerable structural rigidity of the hull and trunk to make it work (retract/extract and stay in place) properly and reliably, and because the mechanisms for retraction and locking increase the maintenance burden, costs and probability of failure.

    Hope it helps. Cheers
  3. WindRaf
    Joined: Oct 2014
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    WindRaf Senior Member

  4. Minthihakyaw
    Joined: Apr 2015
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    Minthihakyaw Junior Member

    Thanks a lot ur replies are precious for me :) I will try best
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