Displacement boat - speed

Discussion in 'Boat Design' started by Duco84, Apr 11, 2015.

  1. Duco84
    Joined: Feb 2014
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    Duco84 Junior Member

    Hello? Does anybody have experience with adding stern (something like on menorquin) plate on boat like this one from photo? What I can except regarding the speed and stability? Currently, top speed with 100hp is 8.5kn.
     

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  2. Duco84
    Joined: Feb 2014
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    Duco84 Junior Member

    I plan to add stabilizer like on this photo
     

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  3. TANSL
    Joined: Sep 2011
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    TANSL Senior Member

    Many current "menorquinas" are built with aft platform. Very useful as bathing platform, I do not think it will improve the speed or stability.
    If what you want to add are sponsons, the result can improve trim and stability. With a speed of 8 knots do not think it will improve the speed.
     
  4. Duco84
    Joined: Feb 2014
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    Duco84 Junior Member

    My plan is to add sponson, length about 4m
     
  5. TANSL
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    TANSL Senior Member

    Then you should explain the problem you have, what you want to achieve with sponsons, to calculate its volume, shape and position.
     
  6. Duco84
    Joined: Feb 2014
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    Duco84 Junior Member

    I want to achieve higher speed and stability. At top speed the trim is about 60cm.
     
  7. messabout
    Joined: Jan 2006
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    messabout Senior Member

    You say that trim at top speed is 60cm. Does that mean that the bow of the boat is 60cm higher than when the boat is at rest? Or does that mean that the stern is depressed 60cm ?
     
  8. Duco84
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    Duco84 Junior Member

    The stern is depressed aboat 60cm
     
  9. DCockey
    Joined: Oct 2009
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    DCockey Senior Member

    What is the length of the boat?

    What is the speed with 50% or 75% throttle?
     
  10. Duco84
    Joined: Feb 2014
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    Duco84 Junior Member

    L=11.4m,
    Lwl=10.8m,
    B=3.35m,

    Propeller: D=650, H=580,
    Enigine 100hp, 2000rpm, ratio 1:2.9,

    1000rpm - 6.5kn
     

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  11. Pericles
    Joined: Sep 2006
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    Location: Heights of High Wycombe, not far from River Thames

    Pericles Senior Member

    Duco84,

    Your vessel is just right the way it is. It is fit for purpose. Adding sponsons will greatly increase wetted surface & drag, so you would probably need more horse power.

    To illustrate your predicament, there was a tourist on holiday & driving a hire car, who had become lost in the countryside. He stopped to ask a local farmer the directions to return to his hotel.

    The farmer was silent for a few moments & then said to the tourist, " Well, if you want to get back to your hotel, I would not start from here".

    There is this Jetpac system. http://sealionmarine.com/products_en.php
     
  12. TANSL
    Joined: Sep 2011
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    TANSL Senior Member

    A 5% trim is a lot. You are right, you should add volume aft to reduce that trim, or change the weight distribution. I think the latter is more advisable, if possible.
     
  13. nzboy
    Joined: Apr 2011
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    nzboy Senior Member

    I agree with pericles .This boats original design was for 30hp motor for efficiency at around 6 knots .What happens when you add more power is that it actually gains lift on the flat mid section and lifts the bow and hence pivots and sinks the stern.You may add water tanks forwards on each side .This may improve stability and trim .
    I think you need just to enjoy going slow and sipping fuel or get another boat that fits your need for speed
     
    Last edited: Apr 12, 2015
  14. Mr Efficiency
    Joined: Oct 2010
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    Mr Efficiency Senior Member

    You might finish up with a boat that handles quite differently with the seas running with it, too.
     

  15. WindRaf
    Joined: Oct 2014
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    Location: Italy

    WindRaf Senior Member

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