SWATH vs Catamaran question

Discussion in 'Boat Design' started by Red Dwarf, Feb 13, 2013.

  1. Red Dwarf
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    Red Dwarf Senior Member

    Please critique this idea.

    Start with a SWATH type hull but have it ballasted so at rest in smooth water the hull is only 95% submerged. This provides normal stability at rest so you don't have to worry about where people on the boat are standing.

    Then when in motion, for example 10 knots, use the control planes to pull the hull down to a true SWATH mode. The control planes are just small wings so I expect they have decent L/D. If the L/D is 20:1 5000 lbs of down force may increase drag 250 lbs. Of course the other option is to pump in water to lower the hulls to SWATH mode draft.

    In this video the control planes clearly have more than enough authority to vary the ride height, look at the 2:05 minute mark. http://www.youtube.com/watch?list=PL0BD4D97C5818A05F&v=c13IrmOF4eE&feature=player_detailpage#t=121s
     
  2. BMcF
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    BMcF Senior Member

    The SWATH (A&R) that you provided the video for certainly does not have the control authority in the appendages to vary the draft..

    Otherwise..you have it backwards in your first hypothetical and correct as an aside at the end of that. What has been done in practice by Swath Ocean International, JMS, and MAPC, and others, is to take very inherently unstable extreme SWATH designs and ballast them down with water when docked or manuevering slowly..and/or include larger appendages and rely on those for lift and to increase cross-structure clearance underway. Then the ballast is pumped out and the appendages used to provide support for some of the vessel displacement as the speed increases. The MAPC HYSWAS is probably the most extreme example of that in an applied sense, but A&R are building one like that at this very moment, and there are other examples.
     
  3. Ad Hoc
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    Ad Hoc Naval Architect

    We did the same sea trial tests on the SLICE....its like a roller coaster ride, in flat calm sea at the push of a button.
     
  4. Submarine Tom

    Submarine Tom Previous Member

    YOU were on SLICE!

    Funny you didn't mention that when we spoke of it earlier.
     
  5. FAST FRED
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    FAST FRED Senior Member

    When I look at most Swath style boats , wonder why did they not just modernize the decades old Box Keel concept.

    Many claims were made for modern style box keels that take the majority of the displacement about their Superior Sea Keeping ability.

    In GRP the box keel can be as shapley as modern hydrodynamics require with little building hassles.
     
  6. BMcF
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    BMcF Senior Member

    I should have been clearer; I meant using foils to control/change the "static" draft, of course. Control of heave, pitch and roll motions about the mean condition is another matter altogether and forced-response tests are always fun. It can also be "interesting" to see what happens when yard personnel re-install the stabilization gyro backwards druing a refit.....and you turn the system on underway not realizing that. :cool:
     
  7. Red Dwarf
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    Red Dwarf Senior Member

    Yes you are right I was thinking of it backwards. I was thinking of getting the draft as small as possible but that only applies to shallow water use. As you said it is better to sink the hulls to the primary structure for stability when stopped.
     
  8. yipster
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    yipster designer

    Yep, since dynamic control is key does make you think of fast one legged swa's as we have seen some demonstrators of in the past
     
  9. BMcF
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    BMcF Senior Member

  10. Ad Hoc
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    Ad Hoc Naval Architect

    Yeah…I saw this recently. It’s a variation on a theme, been done before.

    The Japanese TSL-F back in the early 90s, the other which I’m sure you know more about the HYSWAS way back and also more recently at UCL and their Tri-SWACH Frigate.
     
  11. yipster
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    yipster designer

    as we all like pic's

    [​IMG]TSL-F
    TSL-F looks good for her 20 year :D

    [​IMG]
    i had this demonstator in mind, stuffed with electronics

    [​IMG]
    still interesting i find this swath foil

    [​IMG]
    stevenson build a small bulb swa, as former forum member Rick Willoughby did a bulb with 3 floads
    and pointed out that for a small swa the bulb should be at least 3 diameters below the surface

    [​IMG]
    Tony Graiger drew a swath with nose foil

    [​IMG]
    others imagine wig swaths

    [​IMG]
    as this recently winning design of witch i think it fly's backward :confused:

    [​IMG]
    saw also some jets and supercavitation pics


    with Bolgers boxkeel hardly yet mentiont wiki
    answers original posters question probably shorter
     
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  12. Leo Lazauskas
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    Leo Lazauskas Senior Member

    Would you regard them as successful vessels?, i.e. fulfilling their SOR at a
    reasonable price?
     
  13. Ad Hoc
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    Ad Hoc Naval Architect

    Aaaahh..there in lies the $1million question.

    What was their SOR...seakeeping...only..or cost with seakeeping, or what??. Hard to say.

    The SLICE, excellent seakeeping...probably one of the best vessels out there bar none. But the cost... wow...$$$$$$$.

    There is no one size fits all....as alwasy :eek:
     
    Last edited: Feb 18, 2013
  14. BMcF
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    BMcF Senior Member

    That is remarkably similar to the lifting-body demonstrator built by Navatech some 10 years ago..HYSWAC, I believe they called it.
     
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  15. BMcF
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    BMcF Senior Member

    Here are a couple shots of the hybrid we built and tested a decade ago. Super-slender monohull supported by foils and twin lifting bodies. The 3D rendered view shows a typical flying configuration relative to still water surface.

    Of interest, perhaps, was that we proved we could operate quite well with those "bulbs" very close to, even touching, the mean water surface (the undisdurbed surface).
     

    Attached Files:

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