Hydrofoils/SWATH question

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

  1. jehardiman
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    jehardiman Senior Member

    Oh, I understand, but I'm not sure everone else does. In terms of powering and structural efficency, the law of cubes works against distributed hullforms and those that use area for support and for monohulls and those that use displacement for support. There are many things that work in small test items that can never be scaled beyond a certian point. Both you and I have pointed this out in prervious hydrofoil and SWATH design threads. I just wanted to make sure that everyone understood that there is an upper (and lower if you have a given load requirement) limit to these types of things.

    So what was the testbeds capacity as a % of total weight?
     
  2. BMcF
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    BMcF Senior Member

    Roughly 17% "useful" or "variable" payload fraction. Quite high for a scale model actually and one of the benefits of building such a large one. We've built many self-propelled models (manned and unmanned) where it was barely possible to have it come in at the correct scale weight for full-load-displacement. The last model we built for ONR was 57' LOA and remotely-controlled and we still couldn't get it built under half-load displacement. Some things just don't scale down that well.;)
     
  3. Red Dwarf
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    Red Dwarf Senior Member

    BMcF - Thanks for posting so many details on that project. It looks great and very promising. One thing that I find intriguing is your statement that it rides well in 1.5m seas. The hull doesn't look like it is even close to 1.5m out of the water. Are you saying the wave tops hitting the hulls doesn't appreciably upset the vehicle?

    Now if you go back to page one and some of my thoughts, I think I am on the right track as your project already tested and proved similar concepts.

    So back to my needs. Do you think the same concept scales down in speed. I am talking about a 20 meter vehicle of which 50% of its displacement is submerged bodies and 50% foil borne. I have no interest in speed just efficiency. I want a 10-12 knot cruise and a 15-20 knot top speed. I expect the hulls to be out of the water well below 10 knots, maybe 5-7 knots.

    The 50% displacement split is just a wild a$$ guess and means nothing. I imagine a run of simulations needs to be run and determine the best balance of foil borne vs submerged bodies lift.

    Using the 50% ratio I ran some numbers and to lift off at 3m/sec (5.8 knots) I would need 14m^2 ( 150^ft) of foil area. If that is split 75/25 between two foils the larger is 10.5m^2 and the smaller 3.5m^2.

    I would appreciate your input. Honestly the hardest parts of this concept is propulsion. I have kicked around a dozen concepts and they get complex quick, but I'm sure you already know that and are chuckling at how naive I am. I don't mind, playing with design concepts is fun and keeps me out of the bars, mostly.
     
  4. Ad Hoc
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    Ad Hoc Naval Architect

    Hmm..i tend to shudder when i hear companies say they "invented" an XX and YY concpet/mix of hull forms, or whatever.

    Not disputing the "invention" per se, just that fact that in order to protect something they think is wanted by the whole world, because they love it and spent some much blood sweat and tears, it requires a patent and thus stops innovation...or research into the "invention" for real independent validation.

    It's just a shape. The real "invention" is the technology that is required to make such a hybrid work. Since without such, it is just another shape collecting dust until someone "invents" a method to make it workable :)

    The Typhoon Euro-fighter is a good example. It can only fly by the 4 on-board computers keeping the naturally unstable craft, stable for flight. What is the invention...an aircraft a shape that has wings (unstable or otherwise), or the technology that makes it an aircraft and fly?

    Unnecessary patents...it's one of my bugbears that ruins innovation and research for the sake of "I have the holy grail"..when in fact they don't and no one usually cares either.
     
  5. BMcF
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    BMcF Senior Member

    That is exactly how it is. You are sporting along at 20-something knots in 1.5m seas and the only disturbing part of the ride quality is the "bumps" from the cross-deck structure hitting waves as they pass. No effect on vessel flight attitude; its flying off the gyro and that bow height radar mounted on the frame stuck forward of the bow.
     
  6. BMcF
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    BMcF Senior Member

    Me too. We own no patents and have never applied for one. Yet we've made more invented and patented concepts fly than probably anyone else.

    Observing the results...some good, most bad..is probably why we wouldn't spend money on patents.:D
     
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  7. tomas
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    tomas Senior Member

    Nice. Looking forward to more info.



    How far did those projects go?
    Not much past the scale model tank testing I hope...
     
  8. tomas
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    tomas Senior Member

    Hi Red Dwarf.

    His project is exactly what I was getting at earlier but I didn't want to speak on his behalf since my knowledge is tiny (I'm a nautical noob).

    I did want to say that even though he states a successful result for the project discussed here, he is still being modest. His active stabilization expertise and experience is vast and he's generous as well. You should search the forum for his previous contributions. Very interesting and informative.


    I always laugh when new members take issue with his posts, or challenge his knowledge.
    Ditto for Ad Hoc, Par, Richard Woods, and many others.
    (Some people don't like having a bucket of reality poured on their head it seems.)

    They make this forum a fantastic resource.
     
  9. BMcF
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    BMcF Senior Member

    No. Sadly to say..back in the wild and crazy days of the late 80s and early 90s fast ferry craze, many really crappy designs hit the water.:(
     
  10. BMcF
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    BMcF Senior Member

    Thanks for that..and those fellas do know their game. And some...probably not you..but some would probably be surprised how far back that some of those same names go when it comes to collaborating on successful projects.;)

    That Ad Hoc character and I, for example...we're both about due to have the same cute oriental gal wiping the drool from our chins as we nod our heads and doze off.
     
  11. Ad Hoc
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    Ad Hoc Naval Architect

    What...again!! :eek::eek::eek:

    The "cute" one that 'attacked' me in the "you must come to our bar so we may entertain you" in Pohang...eeekkkk!! She had more foundation cream on her face than the foundations of the Burj Khalifa. Those were the days ;)

    Mind you, not all were moose's :p
     
  12. BMcF
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    BMcF Senior Member

    I can't forget the nice momma that was not going to let me leave her 100 square foot dining establishment in Ulsan without one of her daughters honestly betrothed and in my trail. I might have sprinted away even. I'm sure I tried to. I could not accomplish that now.:rolleyes:
     
  13. BMcF
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    BMcF Senior Member

    Say, Ad..speaking of all those great times..the Koreans are close to building something that looks like X-craft. ;)
     
  14. Ad Hoc
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    Ad Hoc Naval Architect

    The X-Craft ala BMT basic slim cat type?...no, didn't know that. Any public info?
     

  15. BMcF
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    BMcF Senior Member

    Nothing public other than their "expressions of interest" and visits to the US last year.

    But maybe more in a few weeks...;)
     
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