adding keel to deep v

Discussion in 'Stability' started by gtflash, Jan 20, 2011.

  1. gtflash
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    gtflash Senior Member

    What would be the pro and cons of adding a keel to a deep v planning hull capable of 35knots, would it stop it planning, or push its nse down, or just reduce top speed and increase stability at rest??
     
  2. gonzo
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    gonzo Senior Member

    Less speed, more fuel consumption, possible erratic handling, unbalanced trim.
     
  3. Tad
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    Tad Boat Designer

    And no additional stability at rest, less in fact as the additional volume floats the boat higher and reduces waterline beam.......

    Now if you are talking about a ballast keel.......that's a different story
     
  4. tom28571
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    tom28571 Senior Member

    Tad,

    Bite your tongue. Why would anyone add ballast to a planing hull? Certainly not to one of yours. Then again, we might like to know why the OP wants to add a keel to a deep V in the first place?
     
  5. Tad
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    Tad Boat Designer

    Biting...ow!....why?.....who knows?
     
  6. gtflash
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    gtflash Senior Member

    OP??

    Thinking a minimal design, similar to pictured, more than the need for adding a keel, im more interested in the pro and cons.. such as gonzo reply.
     

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  7. baeckmo
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    baeckmo Hydrodynamics

    With a keel you may end up with a hull that is heeling over and planing on the keel and one side of the bottom, depending on proportions of (keel area)/(bottom area) and speed. It has been done, this is what happens with some overpowered semi-displacement hulls. So, unless you are prepared for a considerable amount of trial and error: DONĀ“T go that route!
     
  8. PAR
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    PAR Yacht Designer/Builder

    That's a skeg not a keel, though it's likely attached where part of a keel would be, if that particular boat actaully had one. As a rule you don't want appendages or other protuberances under the boat if you can avoid it on planning hulls.
     
  9. Willallison
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    Willallison Senior Member

    As PAR stated, that's a skeg rather than a keel - probably added more for prop protection than any sort of stability - which could be improved or reduced as others have said.
    It doesn't really look like a 35 knot boat either...
    A better way to improve initial stability (whilst at rest) in a deep-v is to have a hole in the transom to allow water to fill a ballast tank whilst at rest. The water can then freely flow out once the boat starts to pick up speed, so you're not carrying around any extra weight or additional wetted surface. This is easier to achieve in outboard powered powered boats, of course...

    oh... and OP is short for original poster...
    bloody acronyms can drive you mad, I know!;)
     
  10. Mr Efficiency
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    Mr Efficiency Senior Member

    Surely the OP wasn't looking to increase stability ? Certainly no joy in the keel idea there. With the ballast tank idea, no doubt has some merits, but you need it to be full with no slosh factor, and vented well to allow quick draining on take-off.
     
  11. Willallison
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    Willallison Senior Member

    I don't know what he's trying to achieve as he hasn't told us...
    Could be an imrovement in initial stability whlist at rest, could be an improvement in dynamic stability whilst underway... who knows....

    The problem with deep-vee's is that in order to be suffuciently submerged so that the chines are immersed - so giving them much better initial stability at rest - they generally need to be quite heavy.
    The open transom is one solution to the problem and I've been on a number of boats where it makes a hguge difference. The earliest probably being the Bertram 25 when they came out with OMC Seadrives (basically o/b's). The boats were faster and more economical than their sterndrive counterparts, but suffered badly from having the chines out of the water at rest.
    You are correct, however, the "hole" on the transom needs to be as big as possible and vents are required in order for it to fill and empty quickly.
     
  12. PAR
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    PAR Yacht Designer/Builder

    I gathered that the original poster wanted to know the pro's and cons, which he should have surmised by now. I don't think he's looking to install a "keel" on his Bayliner, but who knows.
     
  13. tom28571
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    tom28571 Senior Member

    gtflash,

    My first comment was playfully directed at Tad. The second was a question to you, to which you have not replied. Obtuse questions get obtuse answers. Most here would rather not have to guess at what the question really is. There is no reasonable reason to put a keel on a 35kt planing deep V.
     
  14. Tim B
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    Tim B Senior Member

    The only significant benefits of a skeg on a planing boat are to fair in the propeller tube, and to change (usually increase) the directional stability of the hull. Effectively, it's like increasing the deadrise angle, and it can be used to improve the handling on a shallow V (i.e. 10 deg DR) hull. Deep Vs (over 18 degrees typically) have little need of it, unless there really is a problem with directional stability.

    The effect on static stability and roll damping are negligible. Cons? It adds drag. It may actually de-stabilise the boat in certain down-seas conditions if you make it excessively large.

    Cheers,

    Tim B.
     

  15. PAR
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    PAR Yacht Designer/Builder

    Deep V's can be impressively stable on sand bars . . .
     
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