modified vee rocker hull with jet - planing/porpoise

Discussion in 'Hydrodynamics and Aerodynamics' started by richard gray, Jul 29, 2013.

  1. richard gray
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    richard gray Junior Member

    I intend to use a jetdrive to push a 20 ft aluminium hull. 6 degree floor rise , keel has 6 degree of rocker starts at 6 ft forward of transom. i think it will get up on plane ,but may porpoise? how will this shape affect the jet nozzle ,will it be to level at speed the jet points down 4 degrees from level ( factory spec) the bottom at inlet is as manufacturer suggests, but no info on the rocker in hull?
     
  2. PAR
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    PAR Yacht Designer/Builder

    I'm not sure how you're measuring the rocker, but 6 degrees of buttock angle will cause the bow to be very high. Post some pictures of her profile.
     
  3. richard gray
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    richard gray Junior Member

    Par: the rise of keel is 4 degrees. the question is, if the hull is in plane the bow should drop to a condition where the bottom is in a 2 degree rise, i know the jet drive points down to aft at4 degrees, so it should force bow down as it goes into plane. at rest the front 2/3 would be a 3* rise and last 7ft to transom would rise 3* so it is a rocker bottom. i guess this will affect the planing effect, and may porpoise. the balance is just aft of midship at engine /trans. i only have lines plan and 1/4 scale model shown at (members list )site.
     
  4. PAR
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    PAR Yacht Designer/Builder

    Is this the project I talked to you about this morning?
     
  5. richard gray
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    richard gray Junior Member

    Par i thinks so? check my photos on member list site Richard Gray
     
  6. JSL
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    JSL Senior Member

    A drawing would really help.
    A bit of rocker on a fast planing hull is common but 6 degrees is a lot.
     
  7. richard gray
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    richard gray Junior Member

    rocker hull at jetdrive

    JSL ; i can reduce rocker to 4 degrees. and flatten and widen the last 6 ft. aft. i have not modelled the aft end yet but crude lines plane is on the members list site.
     

    Attached Files:


  8. JSL
    Joined: Nov 2012
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    JSL Senior Member

    Whatever that 'thumbnail' is, it isn't much help. Once a 'Lines Plan' (showing Plan, Profile, and Body Plan) is posted, contributors might be able to make some useful comments.
     
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