Hydrofoils/SWATH question

Discussion in 'Boat Design' started by Red Dwarf, May 31, 2013.

  1. Ad Hoc
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    Ad Hoc Naval Architect

    You have that in a swath, as there are 2 hulls. BUT, and this is the really really impotent part, since it has a low waterplane area, the TPC is small (don’t confuse with reserve buoyancy, that’s a misnomer). So any weight moving about can, I stress can, easily affect the attitude of the vessel. The smaller the swath the more pronounced this effect. Or in the extreme case of the SLICE, when you walk across the deck, because the WPA and GM are so low, you could initiate a small list.

    And this is the whole point of design. A design does not mean just the shape of the hull. The hull shape is just one small element that must satisfy the SOR. There is so much that is required to design successful vessel, whether mono, cat, tri, swath etc…it is a multidisciplinary approach and must be approached as such, not a myopic singular objective. Since a singular objective comes at huge cost, contrary to popular opinion.

    If you want a “stable” boat but with good seakeeping, you then need to define “what else…”. Since there are many other solutions to this simple SOR, but I can guarantee you not all, if any may please you, but it does not mean it can’t be done. Just means it does not satisfy “your” SOR, such as budget or size etc.

    And then you will find, just as any naval architect does, to fulfil the whole SOR (not just 2 items) requires compromise. But if the whole SOR is essentially a superior seakeeping hull (singular SOR), then your compromise is the aforementioned and you just live with it for the sake of the one goal.

    A Ferrari will get you from A to B just as a Ford F150 or Toyota Prius will….the “whole package”, the SOR, will dictate which is the best compromise solution. The Ferrari is fast, but expensive and no luggage space…the F150 loads of luggage/pick up space, but not ideal for going around corners at high speed and poor fuel consumption, the Prius cannot go from 0 -60 in 3 seconds, nor carry a tonne of wood chipping back the garden but is excellent fuel consumption etc etc. There is no holy grail or magic bullet, your SOR dictates which is the best available option.
     
  2. 1J1
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    1J1 Senior Member

    A catamaran hydrofoil would be stable at the rest than SWATH while keeping the highspeed feature. And with lifting bodies instead of ordinary foils it would be a low speed hydrofoil, where since lifting bodies displace some volume, the hull might be more streamlined & of less buoyancy.

    Other option for SWATH at the rest might be having special pontoons for stabilization.
     
  3. BMcF
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    BMcF Senior Member

    This hybrid combination of hydrofoil, lifting body and SWATH worked very well on a rather unusual trimaran hull design..
     

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  4. dskira

    dskira Previous Member

    Sorry, it doesn't mean squat.
    Please show some plans or some exemples.
     
  5. 1J1
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    1J1 Senior Member

    An exemple is right above you, besides as a trimaran (!).
    You also might visit Navatek Ltd. and see their works, many interesting stuff to discover.
     
  6. daiquiri
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    daiquiri Engineering and Design

    Interesting, but I can see a lots of parasitic drag in that picture. It can be done much much better.
     
  7. jehardiman
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    jehardiman Senior Member

    True, but what would be more interesting would be a photo of the main propulsor...because for d..n sure it's not the outboard hanging on the back.

    Small, fast, efficient, stable...can't have them all.
     
  8. dskira

    dskira Previous Member

    On the picture of the post number 18 I count seven frontal penetrations like seven stem. A huge weted area, and a very complex system of different shape and buoyancy.
    How many horse power, and what is the reason for this structure.
    I think it is possible to do everything, but the reason is why?
    I saw on SWATH designed by Ad Hoc in 2002 I liked very much. The engines were on the uperside of the boat, which means very easy to access and maintain, the shaft very long going through the lower submarine shape, meaning no need for a real watertight shaft system, a tube will be enough.
    This SWATH was in my eye so logical in simplicity, that I am sure Ad Hoc spend a great amount of time designing it.
    My point of this story is: making things complicated is easy, making them seaworthy and easy to run is difficult.
    The Navy spend billions of dollars making prototype they abandon as soon they are done. They are not an example to follow, their R&D is dysfunctional, they are just a waste of tax payer money in that department.
     
  9. Red Dwarf
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    Red Dwarf Senior Member

    Any links to Ad Hoc's SWATH design? I would like to see a simple well designed SWATH.
     
  10. Ad Hoc
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    Ad Hoc Naval Architect

    I prefer to remain anon..since i come on her to comment and provide advice where needed. I'm not on here to advertise myself. Just provide technical assistance...
     
  11. Red Dwarf
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    Red Dwarf Senior Member

    I understand and thanks.

    I just thought if there was a picture already out in the public domain a link would be helpful.
     
  12. BMcF
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    BMcF Senior Member

    You are correct. Propulsion was from two outboards hanging on the back.:cool:
     

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  13. BMcF
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    BMcF Senior Member

    I'm always keen to see how others have done things better, of course. Please post your example(s).

    Here's another angle, running 32 kts in calm water this time. Required power was quite low; as best I recall she was soaking up approximately 330 HP in this condition. (integrated real-time thrust measurement system; in addition to the data from the flight control system, the onboard data acquisition acquired some 70 channels of data in all...including an extensive array of static pressure sensors embedded in the lifting bodies and foils.)
     

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  14. BMcF
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    BMcF Senior Member

    Really?
     

  15. Mr Efficiency
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    Mr Efficiency Senior Member

    What is the weight of this vessel in the pix ?
     
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