What size model should represent a vessel design in life testing?

Discussion in 'Boat Design' started by kvsgkvng, Mar 27, 2012.

  1. Leo Lazauskas
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    Leo Lazauskas Senior Member

    There is a paper by McKesson and Doctors in that bunch of FAST 2011 papers I mentioned entitled:
    "Scaling of Resistance from Surface-Effect Ship Model Tests".

    There's an interesting take on using weight (which is usually known quite accurately), instead of wetted area (which is not known well) in some scaling operations.
     
  2. BMcF
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    BMcF Senior Member

    Chris may or may not have taken entirely in to account the hideously tedious but (we always believed) necessary exercise of deriving the exact wetted surface area from the tow tank pictures (with the painted grid on the models for refererence, of course). It was that procedure of subtracting, correcting, and then adding back in the corrected values that resulted in vessels like the Skjold hitting their predicted speed targets exactly. But to put credit where due, that procedure was perfected by the folks at David Taylor and the other basins that were developing those procedures and methods back in the 70s. I've only used what they documented, but to good effect.
     
  3. kvsgkvng
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    kvsgkvng Senior Member

    Thank you, all

    Thank you all for informatinve answers, I learned that physical modeling is a hot topic with the depth of meaning which I do not comprehend. I have enough information to go on at this moment. I appreciate all answers, positive, neutral and one or two sarcastic.

    At this time I would be overwhelmed with more technical replies, unless the thread turned out to live on its own...

    Thanks again, all good people.
    Best regards, kvsgkvng.
     
  4. Leo Lazauskas
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    Leo Lazauskas Senior Member

    He does mention using gold strips on the inside and outside of the sidehulls
    to measure wetted girth, but only at three stations.
     
  5. BMcF
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    BMcF Senior Member

    I could see that method being quite expeditous - as well as valid - for higher Froude numbers where the shape of the contact surface area is neatly more trapezoidal with a straight-line fit to the surface elevation.

    At lower Froude numbers and in the drag hump region(s), the surface elevation and hence wetted surface shape is too complex to estimate it accurately using any approach other than manually calculating the area piecewise from the grid photos. We always gave that job to the new hires. :D
     
  6. Leo Lazauskas
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    Leo Lazauskas Senior Member

    I tried to get a rowing shell builder to add a "graph paper" grid on
    the boat and told them that they could market it as a "scientific" rowing
    hull. It would make my work easier, but I think they knew that was the only
    real advantage. :(
     

  7. Ad Hoc
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    Ad Hoc Naval Architect

    After we did tank testing I used to do that with the video footage we took, slow mo reply frame by frame...i wasn't even a newbbie :(
     
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