7 M length 3.5 Breadth Round bottom without skeg & single OBM in the center line of vessel

Discussion in 'Boat Design' started by alby joy, Jan 17, 2020.

  1. alby joy
    Joined: Jul 2017
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    Location: india

    alby joy Junior Member

    Hi,

    Recently I was working with a project , a 7 meter length catamaran boat with round bottom hull shape and 3. 5 meter depth.The boat is equipped with 6 kW OBM in centerline of boat with only one OBM.
    Please note that we had no skeg in the hull. At present when we taken the boat for trials. The boat was making round and not able to go straight. Even the OBM kept straight, the boat is making circles.
    Any idea about how to rectify. Can we add skeg to hull ? Do we have calculation to skeg area for directional stability.
     
  2. Squidly-Diddly
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    Squidly-Diddly Senior Member

    how about some pics? your boat is 7 long and 3.5m deep? like a 1/2 circle???
     
  3. bajansailor
    Joined: Oct 2007
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    bajansailor Marine Surveyor

    I will second Squidly's request for some photos.
    I think (at least I hope) he means that the beam is 3.5 m., not the depth!

    How far forward of the transoms is the outboard motor mounted?
    It does seem strange that she just wants to go around in circles.
     
  4. BlueBell
    Joined: May 2017
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    BlueBell Ahhhhh...

    Are the hulls accurately aligned ( parallel )?
    Towed in or out a bit?

    Photos please.
     
    Last edited: Jan 17, 2020
  5. baeckmo
    Joined: Jun 2009
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    Location: Sweden

    baeckmo Hydrodynamics

    The center of lateral area is too far forward, and probably forward of center of gravity. Try to trim her down aft and see what happens.
     
  6. Mr Efficiency
    Joined: Oct 2010
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    Mr Efficiency Senior Member

    Naturally if the drive is more at less at the centre of lateral resistance, the steering won't work, as to why it won't run straight even with motor pointing dead ahead, well that could be attributable to a number of things. Fitting rudders to the stern would be a fix.
     
  7. alby joy
    Joined: Jul 2017
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    Location: india

    alby joy Junior Member

    Happy to inform that we have put additional skeg connected to transom of the vessel.This helped to acquire the directional stability for the catamaran vessel- Depth of the hull was 1.06 m..The hull shape was round bottom hull- displacement hull

    thumbnail_IMG_20200319_181721.jpg thumbnail_IMG_20200319_181959.jpg
     
  8. Mr Efficiency
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    Mr Efficiency Senior Member

    The little motor is 6KW ?
     
  9. alby joy
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    Location: india

    alby joy Junior Member

    Yes it is a 6 kW electric outboard
     
  10. Mr Efficiency
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    Mr Efficiency Senior Member

    Looks like you have made good progress, does that run off your solar panels ?
     
  11. alby joy
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    alby joy Junior Member

    Yes we have around 2 kW solar modules on roof which charges the battery bank of 15 kWH Lithium ion phosphate battery pack. Additional to this we have a genset which can charge the battery pack. Presently boat can travel at a speed of 4-5 knots at 4kw ( We have limited the power).
     

  12. Mr Efficiency
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    Mr Efficiency Senior Member

    That is interesting, but I expect facing headwinds is not your preferred heading !
     
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