FAST2011 Conference Papers Available

Discussion in 'Hydrodynamics and Aerodynamics' started by Leo Lazauskas, Mar 13, 2012.

  1. Leo Lazauskas
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    Leo Lazauskas Senior Member

    Yes. All are for 1993 tonne displacement.
    In SES mode, the sidehulls support 20% of the weight and the cushion supports 80%.
     
  2. Ad Hoc
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    Ad Hoc Naval Architect

    Ahh....make sense now.

    Since you cannot compare a like for like of a cat with an SES at an equal displacement. The displacement of an equivalent SES shall always be more heavier. Unless you can buy fans and ducts and additional power units with seatings to support them and fuel to run them that weigh nothing! :eek:
     
  3. Leo Lazauskas
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    Leo Lazauskas Senior Member

    That 's true, but here I am comparing a hybrid cat/SES in different modes of
    operation. The T-Craft (a hybrid cat/SES/ACV) has to carry even more
    additional weight in the form of side "balloons" which are inflated when the
    vessel is asked to operate over land. Sometimes I wonder if these vessels
    were inspired by movies like "Transformers" :)
     
  4. Ad Hoc
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    Ad Hoc Naval Architect

    This is why it is often difficult, or misleading, to read just the resistance data only. Since get a "design" to work, at that displacement, for which ever option, shall yield different lightships and hence different payloads, at that fixed displacement for that hull. Ergo, not a true like for like compassion if the SOR is the same for each configuration.
     
  5. Leo Lazauskas
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    Leo Lazauskas Senior Member

    Again that's true for most vessels. For the T-Craft and some HCAC
    (hybrid cat/air cushion) vessels the SOR is long range at (say) 19 knots with
    a large amount of fuel and no cargo, then transfer cargo at sea from another
    ship, and refuel with enough to travel at > 40 knots for a short distance.
     
  6. Ad Hoc
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    Ad Hoc Naval Architect

    Aahh..this is where we start to get into the nuances of "design" per se.

    A standard well designed cat, can do this more efficiently and cheaper than an SES. This has been proven for many years. And the simple acid test is that all the SES designs(-ers) make these claims endlessly, yet the proliferation of the SES world wide doing "this" is........nuff said!

    There used to be a 50knot SES running from where I used to live. Interesting ride when clam, wild when rough!!! It didn't last long. Even though politics were involved, it couldn't do the same job for the same money as the cats that run that route now.

    There is no logical reason to select an SES over a catamaran. The UK MoD wasted millions proving this to themselves, despite all the existing evidence; with the PASCAT that is now up for sale at a cost for less than the engine package alone!!!
     
  7. Leo Lazauskas
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    Leo Lazauskas Senior Member

    I agree. The weight and complexity of SES is a real killer. The only
    reasonably successful SES I know of is the 260 tonne Norwegian SES
    "Skjold". I suspect that a cat could do the same job, albeit with a slightly
    lower top speed. However, for a top speed of >60 knots, I can't see any
    alternatives to SES.
     
  8. Ad Hoc
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    Ad Hoc Naval Architect

    Concur.
    But does come at a high price. Also 60knots is great when flat calm..however, as soon as the sea state picks up....hmmm...you wish you bought a catamaran, or have lots of sick bags on board :eek:
     
  9. BMcF
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    BMcF Senior Member

    Uh..that's a 'no'. In fact, one of the key factors in the selection of an SES as the platform basis for the replacement MTB's in Norway was the superior seakeeping. RNoN conducted some extensive side-by-side seakeeping trials in the North Sea, comparing a 35m SES passenger ferry motions, speed and voluntary speed reductions with an in-service "Storm" class MTB and a 38m catamaran passenger ferry.

    The SES won hands down over the other two types; it was not even 'close'. In fact, during the side-by-side trials with the monohull MTB, the SES can be seen in the video as it blazes past the monohull at about 35 knots as the monohull was retiring from the testing altogether and running to seek sheltered water... Seas had increased to over 3m and and steep, nasty waves at that.
     
  10. u4ea32
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    u4ea32 Senior Member

    BMcF, do you have a link to those videos?

    From first hand experience, SES is substantially less comfortable than catamarans: in non-glass-smooth water, an SES requires remaining in seats with seat belts, while the cats do not even in rather dramatic seas. The top speeds are less on the cat, but the SES ride quality (or perhaps more accurately, beating-the-living-s**t-out-of-crew quality) is simply disqualifying for reasonable uses (e.g., when you are not simply trying to kill someone without being as badly injured).
     
  11. Ad Hoc
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    Ad Hoc Naval Architect

    Now how did I know you were going to say that :D

    In my experience of being on one, they are inferior. In certain conditions, they are slightly better, but all around, not. This is also supported by the analysis on the French SES AGNES 200. Vertical accelerations, for example varied considerably longitudinally along the vessel, as well as the transverse.

    They also used MSI evaluation curves which indicated it "should" be ok, but the MSI doesn't take into account the effect of 1 or 2 passengers being seasick in such a small boat; the knock on effect. There were many sea sick!

    It is a case of a differing opinion....I've heard it say SES's are great in increasing sea states. But I'm not convinced, also having been on one in rough seas too.

    I'm sure you're aware they were flavour of the month in the early 90s. I attended several conferences where papers on SESs were always presented. The results were a mixed bag even then. So, for now, i'm still not convinced....despite what the Norwegians say :D
     
  12. BMcF
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    BMcF Senior Member

    I base my take on having personally conducted intrumented sea trials of about 35 of them...not one. And more than few long-distance delivery voyages to boot..from Norway to Greece, for example. And I've commissiomed and trialed easily an equal number of catamarans. ;)

    AGNES was a poor design, btw, and performed poorly. Very poorly. Unfortunately for the future utility and popularity of SES as a 'class', there were other attempts that were also medicocre at best, outright failures at worst.:rolleyes: I can count the truly successful incarnations on one hand..unfortunately.
     
  13. BMcF
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    BMcF Senior Member

    I doubt they were ever posted by anyone; they were mostly RNoN property from those trials (conducted in the late 80s), the personal video taken by one civilian crew member excepting. I have a copy of that old tape somewhere..this might be the prod necessary to go locate it.;)

    Poorly designed SES can and will indeed beat you up. But again..not all were poorly designed and built. :D
     
  14. Leo Lazauskas
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    Leo Lazauskas Senior Member

    I'd be interested to know which ones you regard as exemplary.
    I am trying to put together a set of some reasonable cases. The T-Craft
    and Textron's HCAC are excellent examples to demonstrate two-speed operation.
     

  15. Ad Hoc
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    Ad Hoc Naval Architect

    And there in lies the problem. Credibility. More hit and miss than by "design" per se. Too many variables to allow a common design feature to mature and work successfully.
     
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