Foil assisted multihull design

Discussion in 'Boat Design' started by groper, Sep 29, 2013.

  1. BMcF
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    BMcF Senior Member

    Which one(s)? Some of them were indeed not very kind due to the rather abrupt nature of the motions when wave impacts were involved. The earlier "little" Rodriguez boats rode rough as a cob too; spent many an hour riding on those in Korea and across the French channel....err...English channel...whatever..:p...on Condor's.

    The Boeing boats, on the other hand...
     
  2. BMcF
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    BMcF Senior Member

    You couldn't be more incorrect about the nature of fabricating foils in titanium or about how the x-craft was funded and built.

    I'll leave it at that. I don't recall seeing you or hearing your name mentioned at any of the monthly IPT meetings over the course of x-craft's construction.

    Suffice to say that active motion control via trailing edge flaps on fixed foils - any fixed foil - is typically efficient, cheap and reliable...when properly implemented. There are, of course, plenty of examples of failed foil assisted vessel designs..and failed retrofits as well. Credit certainly due Dr. Hoppe for seeing so many variants of his concept succeed.;)
     
  3. Ad Hoc
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    Ad Hoc Naval Architect

    The RHS 70s. The poor helmsman appeared to be "manually" assisting the craft in extremely rough weather. I could see and hear the hydraulics working double over-time as he man handled the controls from sharp left to right with gusto!

    Yup, a real pig of a ride. Not a pleasant experience day in day out when a SW wind was set in for a few days.
     
  4. BMcF
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    BMcF Senior Member

    I would have guessed exactly those. I should have guessed out loud..I would have won something, right?;)
     
  5. Ad Hoc
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    Ad Hoc Naval Architect

    A nice private karaoke booth for yourself and the heavily make-up'ed old gal to "entertain you" ;) ;)
     
  6. BMcF
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    BMcF Senior Member

    Lovely..but I'd have to pass. Been there,,,done that...was very much younger at the time. I believe it was after I managed to direct the modifications of a certain Korean-built fast ferry prototype over the course of several months, during which time the top speed crept from 34 knots to 51 knots.

    But here I must offer an apology to the OP; this thread has been hijacked terribly.

    :(
     
  7. groper
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    groper Senior Member

    I dont mind the hijack, so long as you offer some help in relation to my problem :) what are your thoughts on this? Id very much value your opinion...

    id also like some information pertaining to foil assisted craft of more moderate speeds, as the fuel burn goes up at high speed no matter how great the efficiency it seems...
     
  8. BMcF
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    BMcF Senior Member

    For every foil assisted cat or tri I've been involved with, including the one we built in house, there is a clear cross-over point where the foils produce a benefit in drag reduction. Many failed foil-assisted projects ..most, in my experience, failed because the designers did not correctly predict where that crossover point was in the overall speed/drag/power continuum. I've been involved in at least two foil-assisted projects over the years where the top speed of the craft actually decreased after adding lifting foils.

    There are many successful variants of Dr. Hoppe's simple foil assisted designs running around today. The key, as has already been noted, is all about the proper placement and balance and an appropriately loaded foil system. Some of those would benefit from a trim able aft foil to deal more robustly with CG variations; we've had discussions with more than one designers using Dr. Hoppe's approach that were interested in methods to automatically control the lift on only the aft foils, for average lift and trim balance, and even for dynamic ride control. The cost of that is usually what kills the idea since most of the Hoppe foils are on fairly small, light and relatively inexpensive cats...relative to the multi-million $ fast ferries that do routinely use active stabilization anyway.
     
  9. Ad Hoc
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    Ad Hoc Naval Architect

    Perhaps this one??: ;)
    http://www.flickr.com/photos/darylchapman/8366244589/

    At the time the strength was the main issue. To get the strength the thickness had to be increased, which of course increased the drag. It's the span that's the killer. Okay on small light narrow hulls, but not so easy on the larger multi-$$ ferries you note. The foil lifted and reduced draft about 20 - 30% if I recall, but net speed gain was zero. It was an odd feeling on sea trials, it felt jittery too. (This was back in 1993!!)
     
  10. Mr Efficiency
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    Mr Efficiency Senior Member

    The span under groper's boat will make foils that are hull-to-hull non-starters imo.
     
  11. groper
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    groper Senior Member

    Im aware of this, but the key information i seek, is how to calculate this point for my vessel... any guidance as to how to go about it?

    Any charts or graphs which plot volumetric froude number vs resistance for a variety of foil assisted catamarans of different configurations perhaps?

    This may have been covered in earlier references given, however i dont have access to them...
     
  12. sottorf
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    sottorf member

    I am not questioning your knowledge. You are probably one of the few people around who does understand hydrofoils well and certainly understands application of ride control using foils very well. You mentioned you have worked on "many actively stabilized hydrofoil-assisted catamarans". Which projects were these? There are not that many to my knowledge.
    The Rodriquez Foilmaster is a niche product in itself. They build very few vessels each year. I speak under correction but I think the last couple of years they have not built any. Are you involved in the development of Rodriquez's FSWH37?

    I have to concede that I did not know that the Katran had active ride control elements but the class notation confirms what you say. The Russian hydrofoils I have personally been involved in were fixed foils.

    I am still of the opinion that that actively controlled foils will be a niche mainly for ride control and perhaps a few other high-end vessels here and there but the majority of applications of true lifting hydrofoils will remain fixed foils. Perhaps I am wrong, time will tell...
     
  13. BMcF
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    BMcF Senior Member

    I agree with that...but from a different perspective. The size and cost of the vessels typically being fitted with the simple fixed lifting foils is such that its typically a non-starter to include the cost and complexity of active control flaps on the trailing edge(s), even though they can be mechanically very simple and reliable. As with anything in the AMV arena, it comes to down to cost v benefit, considering the ultimate end objectives and requirements laid down by the user/owner/operator.

    An example: The transport efficiency, seakeeping and ride quality demonstrated by the Techman a.s foil-assisted and computer-stabilized trimaran design were, as a combination, literally some of the best, if not the best, I've ever measured for any vessel of similar size and speed. However, none were ever put in to ferry service. Why?....the total cost of such performance is/was prohibitive.
     
  14. BMcF
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    BMcF Senior Member

    The only way I know how to go about it is to take the bare hull drag curve for your specific design and start analytically adding foils and foil lift/drag to it. It's very much an iterative process and somewhat tedious one at that, because every iteration of increased lift (via change in foil design, vessel speed, or both) requires recalculation of the bare-hull drag as the immersion and wetted surface decrease.

    For purposes of preliminary design estimates, you can "skip some steps" and define a candidate foil configuration for only the intended operational top speed. But you still need to go back and do the rest of the range to see if you will have the powering margins to get past any drag hump effects and achieve that top speed on foil. That is especially critical for waterjet propelled vessels.
     

  15. sottorf
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    sottorf member

    I fully agree with you - the cost and secondly an industry that is notoriously conservative. Even getting ferry operators to accept the "simple" HYSUCAT design is extremely difficult. Couple such conservatism with too many failed projects around the world by people who don't understand the design issues and it is a hard sell all round.

    What was the transport efficiency and Volumetric Froude number of the Techman. It would be interesting to compare with what is achievable with HYSUCATs for the same Froude №.
     
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