Prop Design

Discussion in 'Boat Design' started by aho2167, Jan 3, 2014.

  1. aho2167
    Joined: Jan 2014
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    aho2167 aho2167

    Happy new year to all!

    I'm doing a group design project and have been tasked with the design the propeller. The only way I know how is by using an iterative process with Bp-Delta diagrams for a given power. Unfortunately, for the vessel that we've got. I can't seem to find a Bp-Delta diagram that fits..
    For example my Bp and Delta for one prop speed is 11.2 and 76.2 respectively.

    Would anyone be able to give me some guidance on this? That would be much appreciated!!!
     
  2. Ad Hoc
    Joined: Oct 2008
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    Ad Hoc Naval Architect

    welcome aho2167

    Don't forget it is Sq.root Bp-delta...not Bp-delta.
     
  3. aho2167
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    aho2167 aho2167

    Thank you, but this still leaves me with the fact that I'm unable to find the information I need for the prop calculations?
     
  4. Ad Hoc
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    Ad Hoc Naval Architect

    In that case it would generally indicate that you're using a gear box ratio that is too high.
     
  5. jehardiman
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    jehardiman Senior Member

    Or using the wrong wheel for the speed and load. Low delta for that Bp is also indicative of too small a wheel.

    Anyway, Aho, what type of vessel is this for? Tugs use very different wheels than an express cruiser. Perhaps we can point you to a different wheel type if we know the speed, thrust, diameter, etc...

    Also see this post if you want to work in Kt-J or Kq-J

    http://www.boatdesign.net/forums/pr...-delta-diagrams-request-37507.html#post454896
     
    Last edited: Jan 3, 2014
  6. aho2167
    Joined: Jan 2014
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    aho2167 aho2167

    First of all, I would like to say i very much appreciate your help on this guys. It is for an offshore windfarms support vessel. The data was supplied to me by the member of our group that made a preliminary design for the hull on Maxsurf. That's where I got particulars from.

    As for the Kq-J nd Kt-Jdiagrams, I've been told that that might be an idea but I'm not very sure how to use them. The trail power was 3790 kW, which was found from the holtrop method, and the speed corresponding to that was 18 knots.
     
  7. Ad Hoc
    Joined: Oct 2008
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    Ad Hoc Naval Architect

    Aho

    How about posting your values (and assumptions) so we can assist better?

    3790 is a lot of horses!! (yeah, i know its in kW)
     
  8. Adler
    Joined: Jan 2010
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    Adler Senior Member

    Do you have any Limit on Propeller's Diameter according to your plans ?
     
  9. bit
    Joined: Feb 2008
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    Location: Trieste

    bit Student

    ???
    RPM prop?
    w?
     

  10. aho2167
    Joined: Jan 2014
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    aho2167 aho2167

    Hey guys, apologies for the late reply, Ive been busy travelling back to university. I've been able to receive a bit of guidance from one of my lecturers who has pointed me in the right direction. He pointed out a few mistakes that I made, which, when corrected, will give me other values for Bp and Delta. Hopefully these values will fit the charts I have.

    Thank you all for your help, I will hopefully not have to get in touch again!!!
     
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