SWATH vs Catamaran question

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

  1. groper
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    groper Senior Member

    Im curious bill, for what purpose was the design idea being experimented with? Other than simply research i mean...

    Was the objective a fast vessel with good seakeeping or simply outright speed, or low resistance across a wide speed range or....?
     
  2. BMcF
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    BMcF Senior Member

    The design was for a 50-knot high-speed pax-car ferry; the demonstrator we built was 1/4-scale. The objectives were what one would expect for that application; efficient high speed operation with best-possible seakeeping.

    The concept actually hit both marks better than many..even better than most..that I've tested over the last 25 years. But that said..it arrived at the "end" of the fast ferry boom and has received little attention. Austal bought some license rights, I believe, but I was not privy to the details.

    The company that designed it (Norwegian) is still pursuing the construction of a service vessel and its not completely gone by the way yet...

    The seakeeping was actually superlative. We could take the 13m demonstrator in seas up to 1.5m (that would be 6m at full scale!!) and still leave a coffee cup resting on the console. The high-speed efficiency and the overall speed-drag performance was remarkably similar to that you would expect from a surface effect ship of similar size (including that pesky drag hump), but without the same speed loss in waves.
     
  3. tomas
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    tomas Senior Member

    So what you are working lately?
    More seakeeping and stability projects?
     
  4. BMcF
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    BMcF Senior Member

    More of the "same" thing really. A stabilized high-speed monohull (missile craft) and a fairly radical high-speed foil-stabilized-and-assisted SWATH prototype are taking up most of our time lately.
     
  5. tomas
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    tomas Senior Member


    :eek: You used high-speed and SWATH in the same sentence!

    I can only assume this is a dual-mode vessel of some kind or, it uses a tremendous amount of fuel with a very long and slender submerged hull(s).
     
  6. Red Dwarf
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    Red Dwarf Senior Member

    Very interesting. Are there any papers I can purchase or download that go into more detail on the design and testing of this boat?

    The lifting bodies remind me of the X-35 and dolphin shapes. In a previous life I did some work with Bruce Carmichael, not boats, air vehicle related.
     
  7. BMcF
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    BMcF Senior Member

    You would be making some pretty darned good assumptions, I'd say.;)
     
  8. BMcF
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    BMcF Senior Member

    A professor out of Cal State-LB was involved in the project and did publish some interesting papers. They were available, some years ago anyway, on the CCDOT web site. I'll see if they are still there when I get a chance.

    Those "bulbs" were instrumented with many surface pressure sensors. Interesting data...a lot of correlation work was done, comparing the measurements with the predictions from some cutting edge CFD tools..
     
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  9. Red Dwarf
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    Red Dwarf Senior Member

  10. BMcF
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    BMcF Senior Member

    You found them. Public domain...so you are good to go.

    ;)


    We still have the hull(k) from that demonstrator (built in 2000-2001, last operated in 2004); free to anyone wishing to duplicate the CCDOTT results ...or to use as a party barge..or....
     
  11. groper
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    groper Senior Member

    Bill, can you give us run down on the pros and cons of underwater lifting body application. Clearly theres a seakeeping advantage, but what about things like resistance and load carrying ability etc?

    Do you think its simply a novel idea or might one day see some real commercial application/advantage?
     

  12. BMcF
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    BMcF Senior Member

    The short and sweet answer (i.e the vague and off-the-cuff one) is that lifting body technology generally falls in a sort of nich between hydrofoils and SWATH, having some of the benefits of each. How far you skew those benefits toward one or the other depends primarily on what lift fraction you put on the bouyancy of the body (and any hull remaining in the water).

    Using our own testcraft as an example. Initially a pure foil-assisted monohull with about 80% of the displacement on the foils, she would reach design top speed of 25 knots with a max payload fraction of approaximately 12% and absorbing a bit less than 300 engine horsepower.

    As a lifting body craft (replaced the original main foil with the blended-wing-body one shown in the pics earlier), the max payload fraction was increased to around 20% and the HP required to move the craft at 25 knots increased as well...but I'd have to go look for the answer to how much.

    The seakeeping performance was superlative for both configurations but I'd have to declare the overall winner to be the lifting body version; the pure hydrofoil variant had the inherently jerky or snappy ride quality many foils have..while the lifting body tended to dampen those higher-frequency responses.

    In the real world application arena..I'm seeing more activity in the area of lfting-body or HYSWAS vessel configurations than I am the area of pure hydrofoils. All of these kinds of beasts are subject to the same concerns for excessive draft and/or strike damage to critical appendages.
     
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