Single step hydro hull modification (help)

Discussion in 'Boat Design' started by nwaters, Jun 12, 2015.

  1. nwaters
    Joined: Oct 2009
    Posts: 81
    Likes: 3, Points: 18, Legacy Rep: 90
    Location: wisconsin

    nwaters Junior Member

    I built this single step hydro based on a old Hackercraft design and have a porpoising issues after 2400 rpms. I believe a CG issue. I would like to fill the bottom of the boat to remove the step and looking for the best solution. I attached two different options and would like to hear some feedback on them. The step design scares me so, I would prefer to have a less efficient but, more stable design. Any input is greatly appreciated.
    Thanks,
    https://www.youtube.com/watch?v=M4GMLahamkw
     

    Attached Files:

    1 person likes this.
  2. messabout
    Joined: Jan 2006
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    Location: Lakeland Fl USA

    messabout Senior Member

    Have you considered using some trim tabs? A pair of adjustable tabs will be easier than rebuilding the whole boat bottom.
     
  3. nwaters
    Joined: Oct 2009
    Posts: 81
    Likes: 3, Points: 18, Legacy Rep: 90
    Location: wisconsin

    nwaters Junior Member

    Messsabout,
    I tried interceptor type tabs, it was really squirrely at higher speeds and galloped at low speed. Tried a fixed tab but, drove the bow underwater. I think a variable or adjustable would work better but, if the tab wasn't up when slowing down or dropping off plane it would submarine the nose under. The fixed tabs were down about 1/4" from level over 8" and I could not get on plane, drove the bow underwaters and almost filled the cockpit. As you can see from these pictures the boat sits very low to the water. Coming off plane sometimes makes the bow go under. I have extra weight in bow to try and correct CG but, can't get enough with before the bow sinks to far. I hope by filling the step I can remove the weight forward so I get some buoyancy back and keep the nose up.
     

    Attached Files:

  4. PAR
    Joined: Nov 2003
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    Location: Eustis, FL

    PAR Yacht Designer/Builder

    Without going though the numbers that should be crunched on a boat like this, I'll bet you need to move the CG aft, not forward.
     
  5. nwaters
    Joined: Oct 2009
    Posts: 81
    Likes: 3, Points: 18, Legacy Rep: 90
    Location: wisconsin

    nwaters Junior Member

    Well, this is a temp filler that I'm starting with...wish me luck have not run it yet. Stay tuned!!!
     

    Attached Files:

  6. nwaters
    Joined: Oct 2009
    Posts: 81
    Likes: 3, Points: 18, Legacy Rep: 90
    Location: wisconsin

    nwaters Junior Member

    Success! Much better but, not perfect. I'm going to add a small wedge at the trailing edge to try and correct the little bit left. I will also play with some weight in aft to see what effects it has on the ride.
    https://www.youtube.com/watch?v=6XX_DIB6qsw
     
  7. Kailani
    Joined: Apr 2013
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    Location: Hawaii

    Kailani Senior Member

    Did you lose anything by getting rid of the step? (other than the unwanted porpoising!?)
     
  8. nwaters
    Joined: Oct 2009
    Posts: 81
    Likes: 3, Points: 18, Legacy Rep: 90
    Location: wisconsin

    nwaters Junior Member

    Kailani,
    I have not lost any noticeable performance. The boat is so overpowered so loss of speed is not a issue.
     

  9. nwaters
    Joined: Oct 2009
    Posts: 81
    Likes: 3, Points: 18, Legacy Rep: 90
    Location: wisconsin

    nwaters Junior Member

    Finished the step fill...now its time to go play:)
     

    Attached Files:

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