Propeller design

Discussion in 'Propulsion' started by 91SARATH, Dec 14, 2017.

  1. 91SARATH
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    91SARATH Junior Member

    Hi all!!

    My doubt is about practical difficulties in design of a propeller which is of 330 mm dia and has to provide 6 knots speed with 100 hp engine.

    Is it feasible to design a propeller of this 330 mm dia?.
     
    Last edited: Dec 15, 2017
  2. TANSL
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    TANSL Senior Member

    I know very little of propellers so I will not be so bold to give you any advice. I just want to point out that getting 6 knots of speed with a 100 hp engine can be very easy or very difficult, depending on the hull you are going to use and regardless of whether the propeller design is good or bad.
    Why do you know that the diameter should be 300 mm?
     
  3. 91SARATH
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    91SARATH Junior Member

    we have got draft restriction and our vessel draft is 0.6 m only.And as per hull clearances we can go of 90mm and clearance from baseline 50mm the remaining dia we can have is 360 mm
     
  4. TANSL
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    TANSL Senior Member

    Perhaps a longitudinal tunnel for the propeller and shaft could be a solution?
     
  5. 91SARATH
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    91SARATH Junior Member

    If we can meet the requirement with design of 360mm propeller,we can keep the hull simple and flat from construction point of view to reduce cost.That is why looking out for solution.
     
  6. TANSL
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    TANSL Senior Member

    It is understood.
    Check then if that hull, with 100 hp, is adequate to reach 6 knots of speed.
     
  7. baeckmo
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    baeckmo Hydrodynamics

    The simple answer is NO! But, as always there is the standard phrase "it depends on....".
    That said, there may be a couple of solutions that are less bad than others, but before we start spinning around these, it would be better if you could show us the hull lines aft (if possible the complete hull), and also the resistance estimates that have resulted in the engine power selection. On top of that, the operating requirements in general (in addition to the draft restriction).
     
  8. gonzo
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    gonzo Senior Member

    You could use a 5 blade propeller to get enough blade area.
     
  9. TANSL
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    TANSL Senior Member

    Something like this one?
    helice 5 p.png
    But, id the solution is in the number of blades, maybe that one could be better
    helice 7 palas.jpg
     
  10. Ad Hoc
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    Ad Hoc Naval Architect

    There are only 3 variables that govern the design of a propeller:
    1) speed of advance - flow of water into the prop
    2) the power being delivered
    3) the rpms of the prop.

    Anything is possible, but your values seem extreme and highly unlikely... BUT, if you had a very slow turning prop (ie large gearbox ratio), it is "possible", but it seems extreme. More data would be need to confirm what is or is not possible.

    Yet you simply cannot help yourself, as always., You start every post this way yet continue to blow endless smoke...
    Realistically you need 20% of prop diameter for tip clearance. The real minimum is 17% and absolute minimum is 15%...with each value less than 20% your prop's performance shall be compromised.

    Indeed, the devil is always in the detail...that's where the fun is... :D:D:D
     
  11. TANSL
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    TANSL Senior Member

    Why are you so kind, my friend? Really, it is not necessary, I will respect you equally:D.
     
  12. Ad Hoc
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    Ad Hoc Naval Architect

    And yet...

    You simply can't stop yourself.....go figure!
     
  13. TANSL
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    TANSL Senior Member

  14. gonzo
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    gonzo Senior Member

    Ad Hoc: I think there is a fourth variable that is important, the clearance/ maximum diameter possible.
     

  15. TANSL
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    TANSL Senior Member

    Gonzo, really what do you think Ad Hoc is talking about when he says :
    Although other experts seem to think very differently. Among other things, as you can see, clearances vary enormously with the number of propeller blades.
    Propeller clearances.jpg
     
    Last edited: Dec 16, 2017
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