Semi submarine hull Te Puke

Discussion in 'Multihulls' started by BMP, Jul 7, 2022.

  1. BMP
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    BMP Junior Member

    What are the performance and safety considerations of a semi submarine hull like these?
     
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  2. Skyak
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    Skyak Senior Member

    Characteristics of modern "semi submarine" multihulls can be found by researching "SWATH" vessels.
    Traditional Polynesian craft are not designed to the same reasoning or materials.
     
  3. BMP
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    BMP Junior Member

    Would a hull like the ones on the tepukes in the video smooth out chop while still rising for larger swell?
     
  4. jehardiman
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    jehardiman Senior Member

    Rising to swell where? As I have pointed out before not many Polynesian designs are found outside of 35 N/S or the 25C surface thermoline. Horses for courses.

    EDIT: Look up a baidarka kayak for how the other half of the world implemented it.
     
  5. BMP
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    BMP Junior Member

    Baidarkas don't make great family boats, and while umiaks do fill the purpose it seems that multihulls do have some advantages, especially in the speed and stability departments.


    If a 30ft boat could cut through 1-2ft wind waves/wakes with little motion but would not bury the bow too much in 4+ waves it would seem like a worth while concept to explore, what would the downsides be for use in higher latitudes?
     
  6. jehardiman
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    jehardiman Senior Member

    But not in transport capacity...which is why there are umiaks.
    Cold water on/in the deck. Polynesian and Inuit are completely different in how they treat the crew exposure to water. Not rising to the wave require entirely different methods to keep the crew warm.
     
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  7. BMP
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    BMP Junior Member

    So if you took a long kayak and a short kayak connected them to a platform high enough that the waves wouldn't break over it and added a small wind shelter and good size sail then equipped the crew with seal gut parkas and pants wouldn't you have the best of both worlds (you could even add a small fire pit so you had a chance to get warm)
     
  8. BlueBell
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    BlueBell . . . . .

    Marshmallows, weiners, open flames... what could possibly go wrong. ;)
     
  9. peterAustralia
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    peterAustralia Senior Member

    jeremy Walker has built a similar canoe from modern materials. He is in New Zealand. Perhaps you should contact him for real world sailing information
     
  10. Skyak
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    Skyak Senior Member

    It can under the right conditions, but it could also fail to rise above in the wrong conditions. This is why I defer to SWATH for study.

    Small-waterplane-area twin hull - Wikipedia

    To simplify, think about the floating hull in frequency response. The change in buoyancy per change in depth is proportional to the waterplane area so that is the spring constant. If the waterplane is small relative to the mass the natural frequency will be low, and if the craft is moving fast through small, short wavelength chop the driving frequency will be high. The mismatch between natural frequency and drive frequency lowers the response. If the same craft went slowly over long wavelength swells it could go over and not through because the wavelength is close to the natural frequency.
    That low natual frequency could be an issue at harmonics of high frequencies or steep faces of large waves. The frequency of incident waves also depends on angle. Furthermore, the paragraph above is a huge simplification to one dimension. To get real answers you need to do the 3D with rotational inertia and force distribution....the hull length relative to wavelength is critical.

    Modern SWATH vessels are calculated, know their limits, and have adjustments to address different conditions. My understanding of traditional Polynesian system is that they were highly skilled and at peace with the world when they set out, possibly never to return.
     
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  11. BMP
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    BMP Junior Member

    Thanks so much, that is about what I thought, but just thinking can get you into trouble.
    SWATH vessels often have active control systems to avoid the problems you mentioned, right?
     
  12. Skyak
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    Skyak Senior Member

    Yep. SWATH craft can adjust mass and buoyancy, and those systems are critical.
    The interesting thing about Te Puke is the one hull goes through the waves and the other is narrow but has a significant and increasing waterplane. Did they just move weight around to alter the wave response?
    BTW there is a very active community on Harry Proa and Rob is out in Fiji now developing a boat for island trade.
    80 foot cargo harryproa | Page 9 | Boat Design Net
     

  13. BMP
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    BMP Junior Member

    I have been following Rob's work with interest. As far as I can tell only the tepukes carry the weight to windward like a harry.
     
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