Speed Optimization - need to calculate the optimum speed for a given voyage

Discussion in 'Boat Design' started by Chris Pap, Jun 10, 2015.

  1. Chris Pap
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    Chris Pap Junior Member

    Daquiri, thank you very much for these valuable info.
    They are very useful and help me a lot.
    I assume that this has to do only with the wind drag.
    Is there anything similar as far as you are know about the wave drag?

    ChrisPap
     
  2. daiquiri
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    daiquiri Engineering and Design

    Check this thesis work: http://www.kth.se/polopoly_fs/1.151543!/Menu/general/column-content/attachment/Alexandersson.pdf
    Lots of things to read and digest in that paper, but it sums up various methods for calculation of added resistance due to waves. At the page 31 it shows a method to develop a simplified formula for added resistance in head waves for a given ship. I have never tried to implement it though, so you're on your own there. :)

    You might also want to check this short thread on that topic: http://www.boatdesign.net/forums/hydrodynamics-aerodynamics/added-resistance-wave-47506.html

    Cheers
     
  3. daiquiri
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    daiquiri Engineering and Design

    Off-topic

    Unfortunately, what you describe is currently a worldwide problem. Personally, when I look at the big picture of what is going on all around us, I am getting convinced that we are witnessing a major turning point in the history of the world - one of those which can radically change everything for better or for worse. I like to think it will be for better.
    Perhaps Mayans were not so wrong, after all... :p
     
  4. rxcomposite
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    rxcomposite Senior Member

    Hot Topic!

    Most of this has been discussed in previous threads and has been participated by the most notables and experienced members. Links to some:

    Seakeeping Standards
    http://www.boatdesign.net/forums/classification/seakeeping-standards-48016.html
    http://www.boatdesign.net/forums/hydrodynamics-aerodynamics/seakeeping-criteria-standards-48010.html

    Required Freight Rate by Daiquiri
    http://www.boatdesign.net/forums/boat-design/another-scaling-question-seaway-48182.html

    Sample calculations by AH- Just posted by Daiquiri
    http://www.boatdesign.net/forums/hy...s/added-resistance-wave-47506.html#post637215

    Transport Capacity
    http://www.boatdesign.net/forums/multihulls/canting-keel-monos-vs-multihulls-13511-5.html#post104220

    Least drag of the hull
    http://www.boatdesign.net/forums/hydrodynamics-aerodynamics/two-hulls-has-least-drag-45172-6.html

    Seakeeping is stability, motion comfort, and a reduction of speed/increase of power in relation to the sea state or Beaufort number.
     

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  5. rxcomposite
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    rxcomposite Senior Member

  6. BertKu
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    BertKu Senior Member

    Last edited: Jun 19, 2015
  7. Chris Pap
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    Chris Pap Junior Member

    Seems I have a lot of work to do.
    So my first priority is about the added resistance (in terms of percent increase) regarding the weather.
    Thank you all very much one more time.
    You gave me far more than a point to begin.

    Chris Pap.
     
  8. BertKu
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    BertKu Senior Member

    OK Chris, we have done our part, now you must do you part and get your qualification WITH CUMLAUDE.!!!!
    Bert
     

  9. S Steel
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    S Steel Junior Member

    Well, a car racing team is in the news in that they design systems based on acquisition of data.

    What is needed here is fuel flow rate, throttle position, engine RPM, ship speed, wind speed, wind direction, ocean current speed, and ocean current direction. All the calculations are avoided just by getting the actual result.

    But moving on, if the ship expects wind and ocean current with-it for 50% of the voyage but wind and ocean current against-it for 50% of the voyage then the ship could use maximum cruise speed with the current and minimum cruise speed when against the current.

    So the calculation is the net headwind or tailwind effect of wind and current on the ship and the percentage of distance of each weather system that the ship is in. This is the weather forecast.

    If the ship has a headwind/ocean-current force of 5 knots for 75% of the voyage but then a tailwind/ocean-current force of 7.5 knots for 25% of the voyage then:

    Headwind leg loses 5 * 7.5 or 37.5 in distance

    Tailwind leg gains 7.5 * 2.5 or 18.75 in distance

    Tailwind leg increases speed by (37.5 - 18.75) / 2.5 or 7.5 knots to regain distance

    The frame of reference is a fixed throttle setting not engine RPM and not fuel flow rate. On the tailwind leg the speed is observed at the fixed throttle setting and then increased by 7.5 .


    Now that's not an authority but just my own idea
    .
     
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