godevil on canoe

Discussion in 'Surface Drives' started by fishon91, Dec 28, 2007.

  1. John O`Neal
    Joined: Sep 2007
    Posts: 85
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    Location: Lenexa Ks.

    John O`Neal Junior Member

    propulsion unit


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  2. Guest625101138

    Guest625101138 Previous Member

    Not as much as I thought initially after doing the numbers. Depending on loading condition the efficiency for the prop shown could go from 58% to say 62%.

    The shrouding in this case provides a measure of safety as well as the thing would be quite a weapon.

    Rick W.
  3. grob
    Joined: Oct 2002
    Posts: 216
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    Location: Cotswolds Waterpark, UK

    grob www.windknife.com


    Thanks for that, do you have any references for this calculation, or do you use a piece of software?


  4. Guest625101138

    Guest625101138 Previous Member

    I have my own prop analysis software only because I can do all sorts of manipulation with different foils. It does not give results much different to JavaProp:

    As downloaded, the options are set for air but you can change them to suit water.
    Density for saltwater is 1025
    Viscosity for water is OK at 0.0000013

    You have to select the type of foil. Most boat prop blades are thin so I usually use the MH 9.8% 500,000 for bigger/faster boats and the E193 100,000 foil for smaller boats. You can adjust the AoA to get a suitable chord.

    I have attached the screen dump from one of the calculations I did for the Whipella. Note that there is a checkbox that can be ticked to have with and without shrouding.

    Effective shrouding will eliminate induced drag so it is particularly effective in heavily loaded applications.

    As far as the boat goes conserning speed and power, I just guesstimated the speed and drag by looking at the video. I was only interested in the relative performance of the shrouding.

    I have seen loading conditions where shrouding has had a dramatic increase in efficiency. Better than 10% gain in efficiency. This gain is offset a little by the extra drag of the shroud.

    JavaProp provides a primarily anylitical result based on the underlying physics rather than relying on empirical data so it gives good understanding of what is going on if you care to work through the various analysis tabs.

    Rick W.

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  5. masalai
    Joined: Oct 2007
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    Location: cruising, Australia

    masalai masalai

    And he hasn't even cleaned the weed growth off :D
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