planing hull with a keel?

Discussion in 'Boat Design' started by George K, Dec 18, 2012.

  1. George K
    Joined: Dec 2012
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    Location: Greece

    George K Junior Member

    good day!
    i am trying to understand if a hull that has been given to us is a planing hull or not. it has a keel, but what worries me is that the the hull towards aft rises and flattens out, to accommodate the shafts and props. a flat aft is good for planing obviously, but what about the fact that it rises?from the front it looks the business: sharp entry, hard chines.
    any thoughts?
     
  2. tunnels

    tunnels Previous Member

    post some detailed pictures of what you got !!!

    Easy to post pictures so we can see what you are talking about !!
    boats with Keels will plane just the dont like turning to much and like to go in a straight line :D
     
  3. PAR
    Joined: Nov 2003
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    PAR Yacht Designer/Builder

    Yep, boats with keels, skegs and other appendages can plane off fun, though as with everything there's a trade off, often as Tunnels mentioned, directional stability.
     
  4. midnitmike
    Joined: Apr 2012
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    midnitmike Senior Member

    Lets have a look at it.

    MM
     
  5. George K
    Joined: Dec 2012
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    Location: Greece

    George K Junior Member

    Hello all!
    Thanks for the replies!we decided to go along with another hull (still keeled as the customer requires it) but at least i am sure this is planing, and i will be sending you pics shortly!
    Can anyone tell me how to calculate resistance? i guess Savitsky is ok but i think this requires a modified version. I have found an online calculator http://illustrations.marin.ntnu.no/hydrodynamics/resistance/planing/index.html

    but this does not take into consideration the resistance of the keel.

    Any suggestions please???
     
  6. JSL
    Joined: Nov 2012
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    JSL Senior Member

    Some drawings or sketches would be really useful
     
  7. CDK
    Joined: Aug 2007
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    CDK retired engineer

    A planing hull with a keel would make a nice ferry. Slowly point it to its destination, then open the throttle and have a beer.
    No crosswinds allowed of course.

    George K, does your customer understand that a planing hull with a keel behaves like a train?
     
    1 person likes this.
  8. daiquiri
    Joined: May 2004
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    Location: Italy (Garda Lake) and Croatia (Istria)

    daiquiri Engineering and Design

    The exact value of added resistance due to a keel will depend on the speed, keel shape and the amount of marine growth on it's surface.
    As a rough guide, with a drag coefficient Cd=0.006 (corresponding to a airfoil-like keel in mid-summer, with some marine growth on it), you might require roughly up to additional 60 HP of engine power (30 HP effective power) for each square meter of keel lateral area, at 30 kts speed.
    Since the power required to overcome friction is speed^3 dependent, it means that - assuming the above friction coefficient - you can calculate the additional power (due to the presence of the keel) via the following formula:
    EHP,add = Vkts^3 / 900
    That power, re-calculated for each given speed, has to be added to the results of that on-line Savitsky calculator you've mentioned.
    Cheers
     
    Last edited: Dec 21, 2012
  9. eyschulman
    Joined: Jul 2011
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    Location: seattle Wa USA

    eyschulman Senior Member

    DE boats have keels some are relatively fast most fall into fast semisplacement catagory. I think poster is really in that catagory without drawings or pictures we may never know.
     
  10. JSL
    Joined: Nov 2012
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    JSL Senior Member

    Several people have suggested a sketch or drawing be submitted to make it easier to understand what is being discussed. I have been designing sail and power boats for about 40 years and one skill I have never mastered is reading minds. Keels come in different shapes and sizes, as do boat hulls.
    One thing I will offer is large keels on a fast boat can often affect the handling. In 2 instances, removing a keel (large skeg) turned the boat from a totally unmanageable beast (ie: dangerous) into a manageable one.
    Wishing you all a Merry Christmas

    (ps: if I have missed a sketch- my apologies)
     
  11. mihkel
    Joined: Aug 2010
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    mihkel Junior Member

  12. Mr Efficiency
    Joined: Oct 2010
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    Mr Efficiency Senior Member

    Looks like a planing hull, you should be telling us about the performance ! You may need to do some work with that exposed fibreglass, no good to have that exposed to water.
     
  13. mihkel
    Joined: Aug 2010
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    Location: estonia

    mihkel Junior Member

    Ill try to make a test run next month. Sanded, cleaned, filled and painted the whole hull from outside and inside. That old boat had so many layers of bad paint on it. Heavy work. But fiberglass showed no cracks and strong.
     

  14. rick gray
    Joined: Dec 2012
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    Location: port coquitlam B.C.

    rick gray Junior Member

    Help to get performance info

    Hello; i have an amphibious vehicle hull in thevworks (posted on search engine (Richard Gray) hope to get help on hull design > contact rickgray@telus.net if you can consult me thanks Rick
     
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