The project fast lightweight power catamarans - is possible?

Discussion in 'Boat Design' started by romanewas, Jan 6, 2017.

  1. TANSL
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    TANSL Senior Member

    I do not know if the correct figure will be 0.1g or 0.2g, or ... but I guess of course it should be quite less than 1g and never greater than 1g.
     
  2. romanewas
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    romanewas Junior Member

    Attached source material. Please look at page 7/8. There is a chart titled: Figure 1.1: Human Appreciations of Accelerations
     

    Attached Files:

  3. kilocharlie2
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    kilocharlie2 Junior Member

    Looking at the video you were impressed with, the main factors for your desired stability (NOT causing sea sickness) level has to do with: 1) upper hull wave clearance; and 2) LOA (no, not LWL) interaction with the swell period, not so much individual waves.

    The video was no where near 2 meter waves. That SWATH in the video would have experienced much more roughness in 6 foot seas. I'd suggest taller and longer for a smooth ride.
     
  4. TANSL
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    TANSL Senior Member

    Taller or smaller has not much sense if not related to wave length.
     
  5. kilocharlie2
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    kilocharlie2 Junior Member

    Yes, it appears that the SWATH in the video was quite comfortable in 1- to 3-foot seas, and was performing quite nicely. The only "bumpy" parts of the ride appeared to be when a wave peak coincided with the swell peak and pushed upon the upper hull, rocking it a bit. But, the video is not like riding in the boat.

    It also appeared as IF the same boat was in 6-foot seas, it would have experienced a rougher ride. I suppose I'd build for slightly worse conditions than expected, and try to keep those customers comfortable.
     
  6. romanewas
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    romanewas Junior Member

  7. kilocharlie2
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    kilocharlie2 Junior Member

    Thank you for posting that chart, Roman. That helps.
     
  8. romanewas
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    romanewas Junior Member

    This is a very important chart. It defines the conditions for a comfortable travel for passengers.
     
  9. Stumble
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    Stumble Senior Member

    I have real doubts about the use of a SWATH here. SWATH's have a lot of surface area, meaning very high running costs, and at about 60' operating at 20kn is going to burn a lot of fuel. If you go longer, then the hull build cost just soars and passenger capacity becomes excessive to needs.

    I would suggest looking at a high speed displacement catamaran instead. It may not handle really large waves quite as well as the SWATH but will likely be an all round better performer at far lower cost.

    Something like http://www.one2three.com.au/c19.html and since there are already boats built, there minimal gamble on the design and operation.
     
  10. TANSL
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    TANSL Senior Member

    My opinion, without being able to provide specific comparative studies, is the following:
    The design of a boat is always a compromise between various parameters many of which may be incompatible with each other. None is reached at 100% and therefore some priorities have to be set. If the main concern is the comfort of the passage, in the terms expressed by Romanewas, I have no doubt that the SWATH is the type of boat he needs.
    In resistance to advancement there are several factors involved. The most important is wave resistance. The wet surface may be smaller on a catamaran but not much smaller. The SWATH minimizes the formation of waves so the total resistance, sure, is less than on a catamaran. But, of course, it depends on the shapes that are adopted for the hulls. On boats with little variation in the paid load, such as passenger ships, SWATH, for the same displacement, has advantages in terms of fuel consumption and power / speed ratio.
    Just my opinion.
     
  11. Mr Efficiency
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    Mr Efficiency Senior Member

    Stumble's suggestion seems a good one, an existing design must exist for this task, if not the specification is unlikely to be met.
     
  12. TANSL
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    TANSL Senior Member

    I totally agree with you, Mr Efficiency, an existing SWATH project is an option that should be taken into account.
     
  13. Mr Efficiency
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    Mr Efficiency Senior Member

    Haha, I doubt a SWATH is the answer, there is a glut of rough water cat designs, I expect a lot less SWATH's off-the-shelf tourist boats.
     
  14. TANSL
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    TANSL Senior Member

    I still agree with you, there are very few SWATH, in the field of passenger ships and in any other field, but the conditions that the OP has proposed can hardly be reached, can not be reached, with a mono-hull or a catamaran, instead A SWATH does have options.
    The problem to be solved is not that the boat can sail with huge waves, but that the accelerations that the passage experiences (the sensation of floating in the air) are as low as possible.
     

  15. Mr Efficiency
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    Mr Efficiency Senior Member

    The link provided by Stumble should help the OP a good deal.
     
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