hull form evolution

Discussion in 'Sailboats' started by rapscallion, Sep 11, 2010.

  1. rapscallion
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    rapscallion Senior Member

  2. Doug Lord
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    Doug Lord Flight Ready

    Thanks, Raps- very interesting...
     
  3. CT 249
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    CT 249 Senior Member

    The wing shape is extreme, but many winged boats have had major issues with wave drag to leeward that have meant that they failed to perform as planned. This shape doesn't look as if it would be any better, to my eye.

    The racket down below when waves funnel down the gap between the hull and wing would be pretty extreme, wouldn't it? And as they are constricted sideways wouldn't the energy be diverted to making the wave higher until it hit the top of the tunnel? What does a few tons of water do when it's constricted into a narrowing channel at 10 knots?

    There is a reason Shining and Maiden (two of the craft that inspired this design) have wings canted up instead of down, surely.

    As far as 8m rockets go, one of the best around would be the Stealth 8m (full cabin accomodation, 9% quicker than the Melges 24) and it has upward-pointing wings a la Shining, not downward pointing ones.
     
  4. Doug Lord
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    Doug Lord Flight Ready

    CT, did you read the PDF?
     
  5. Eralnd44
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    Eralnd44 Wanderer

    thread is better as multihull talk. after looking interest is made and not held as monohull becomes tri. a tri design solution is coming better. this boat expenses to build over plane mono.

    when is good to make trimaran for stabble fast boat then making trimaran to start

    then to make foils when boat is so clear without, no?
     
  6. rapscallion
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    rapscallion Senior Member

    The hull design satisfys the definition of monohull, according to ISAF
     
  7. rapscallion
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    rapscallion Senior Member



    I can't seem to find much information on The Stealth 8 Meter, I used to have some info on the boat, but a hard drive crash took care of that....
     
  8. CT 249
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    CT 249 Senior Member

    Yes.

    p 29 - "it is very hard to predict how the winged hull will perform in a seaway"

    P 29 notes that wave drag interaction will be a major issue.

    It is noted that the wing will only touch the water at high speeds. That may be so in the Med, but in other places where there is an ever-present ground swell and big chop, a section of hull that touches only at 10 degrees heel in flat water (like this wing) will actually regularly be slammed. This effect can cause a very significant reduction in speed.

    "Probably the small portion of wing in contact with the water has created a wave pattern that contrasts the main hull wave system." (p 37)

    "There is a visible resistance hump" at a Fn where the tunnel becomes full (p 42) and when the tunnel becomes full, there would surely be some effect from waves entering the tunnel and later finding it full. Yes, 20 degrees heel is not the normal condition, but neither is the flat water the model was tested in. Fifteen degrees of heel and a couple of metres swell and large chop IS common in many places of the world.

    "Seakeeping and seakindliness were not addressed" (p 51).

    "The added wave internal resistance model has been disengaged in both files,since it would be completely imprecise in the case of the winged hull form" (p 47) appears to indicate that the polars were made without the wave effect on the lee side of the hull being considered.

    "for obvious reasons, it was impossible to view the flow inside the tunnel" (p 41)

    I don't want to come across as anti-innovation, as I'm not - I'm just not into all forms of claimed innovation. But surely there is nothing wrong with pointing out, politely, potential issues with a concept.

    There are always plenty of people to say that it's disrespectful to make comments about a concept, but surely it is equally disrespectful to believe that Farr, Briand, Castro, Manni Frers, B&C, J & V, Finot, Elliott, etc have all been getting it wrong all these years.

    If the dissertation had included obtaining information from someone like Castro or Manni Frers about why they tilted their wings up instead of down, and then included that information into the study, I would have been fascinated.

    I'm not knocking the student, I'm not qualified to judge but it seems like nice work. I'm just pointing out that it may not be a rocketship in all conditions.
     
  9. Doug Lord
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    Doug Lord Flight Ready

    CT, you quote almost all the negative factors associated with this paper and zero(none) of the positive factors. Maybe the designer left them there so that someone like you could create an unbalanced view of the design potential? More likely, he was looking at the design dispassionately and trying to see if the good points outweighed the bad points of this cruiser-racer. It's just a shame that you would present such a one sided, negative overveiw of the balanced assesment of the concept by the designer.
     
  10. Eralnd44
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    Eralnd44 Wanderer

    negative conversstion must be met with eagerly as positive talk for idea to be useful. going the opposite direction only leads to the greasing of concept with out getting in the know of the opposite side. this is the responsibility of the concept if presented as one of whole ideas.

    do you have the answer to the points as made by CT, Mr. Doug, or do you only go to the answer you wish in the talk? if not of the address then it is not of substance and only fancy thinking.
     
  11. Doug Lord
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    Doug Lord Flight Ready

    Not sure I completely understand you Eral but if you read the PDF you'd find that the designer spelled out the positive and negative attributes of the design as best he could with this preliminary work. He noted the potential shortcomings of the design and the design and development work still necessary to reach well informed conclusions about the feasibility of the concept. You would also recognize that there are no "answers" to most of the criticisms the designer made(and CT noted) of his work without further R & D.
    It is one of the most balanced assesments of a new concept that I've had the pleasure to read.
     
  12. CT 249
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    CT 249 Senior Member

    It's not particularly negative to mention one's impressions regarding a factor that the designer COULD NOT ACCURATELY MEASURE - that is, the effect of the wing on drag in choppy conditions and/or swell. And the designer has not covered everything; i.e. how do you bring it alongside a typical dock and get off? There are ways you could do this practically, but some (all?) of them involve extra weight which was not included in the calcs.

    By saying Design A (a new boat) is superior to Design B (existing craft), one is of necessity rating design B as inferior. Why is it so good to assume that Frers, Farr, Elliott, Young, Finot, Faroux, Castro etc got it wrong when it comes to wing design, and that this design gets it right?

    Why is it so good to assume that Maiden HK, Extreme, Shining, Stealthy, the Kiwi 35, the Moore 30, the Rocket 31, just about every Open 60 and several hundred other water ballasted boats are wrong, and this design is right?

    How is it not MORE negative to assume that dozens of designers and hundreds of boats are wrong, than to assume that one designer (who SAYS that he could not measure the issue I mentioned) and one study plan is right?

    The designer here WAS balanced, and DID do the honest thing and admit he could not measure anything. All I'm pointing out is that there are many vastly experienced designers who have launched many water-ballasted winged boats and it appears that their experience is that the factors that this designer KNOWS he could not measure are very important and that they are best avoided by a different shape.

    When I got my first boat, there was another guy building a Moth in the same club with wide hull wings (under the racks) for stability. They soon got cut off, because they didn't work. The Moth hull wings that did work were the much more gradual ones a la Claridge Magnum designs. That is yet another example of a design where wave slap on a wing was an issue, but the main point is to show that such things have been considered for a very long time (and that's ignoring designs from the '60s that used stub hulls) and that there are issues with them.

    But of course Doug, you are right. This boat is perfect. Nothing about it could possibly be improved. Nothing about it is in any way anything less than the complete ultimate, the creme de la creme, the ne plus ultra, the acme of all that man could desire, the cynosure of all eyes, it is transcendent in its consumate faultlessness as the sublime realisation of all things wondrous.

    You're right - no one has the right to dare to even wonder, as a passing comment, whether this design could have the issues that other winged craft sometimes have, because this design moves into a different world, where nothing can possibly go wrong.
     
  13. Doug Lord
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    Doug Lord Flight Ready

    ===========================
    What silly, offensive comments to make! I never said or implied anything like this-you flat out misrepresent what I said.
    This designer was- and is- well aware of the short-comings of this paper and, basically, all he says is that there is potential that should be evaluated further.
    And yet you ascribe all sorts of things to him, to this paper and even to me that neither he nor I ever said, implied or even thought!
    It seems he pushed a button by merely suggesting that there are good points(and bad points) to this design and that it shows some potential that would need to be evaluated further and much more thoroughly.
    He made no outlandish claims that would warrant you implying that he somehow dissed other designers! And I made no claims whatsoever for this design other than that I found it "interesting" and that I thought the designers presentation was balanced and, I think, well done.
     
  14. CT 249
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    CT 249 Senior Member

    People here surely have the right to make comments about designs introduced for discussion. What else are we here for - to be a bunch of cheerleading nodding donkeys?

    I specifically mentioned "The designer here WAS balanced, and DID do the honest thing and admit he could not measure anything." I showed quite clearly that the designer had been honest and insightful enough to discuss some of the issues. Good on him!

    I said I wasn't knocking the student and that the design "was nice work". I didn't attack him.

    The reason I included those quotes from the design study was to show that this designer had the forethought to realise that there COULD be issues with the effects of the wing in a seaway, and therefore that my opinion about the flares was not necessarily going directly against his own ideas.

    Rewind to my first post. I made a comment about ONE feature of this boat, based on experience with winged ballasted monohulls since the '80s and discussion with other designers about wings and flares.

    That was NOT insulting. It was NOT excessive. The designer himself says that he has not been able to test that area, and I merely submitted that practical experience shows that there could be difficulties.

    My final paragraphs of the previous post were, as would have been obvious, NOT aimed at the design, because no designer thinks their boat is actually perfect. My comments were aimed at underlining how stupid it is to pretend that there is any design that doesn't have weak points.

    You keep on saying there are good and possible bad points about this design - that's exactly what I was saying, but you seem to feel that no one else has the right to discuss the possible weak points. Every design has a weakness and surely there is nothing wrong with discussing one that this boat may have.
     

  15. ancient kayaker
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    ancient kayaker aka Terry Haines

    Raps, I have to agree with the criticism here, again, as CT notes, not with any desire to denigrate the writer of the article. He seems scholarly and is making an effort to be open minded, and we should do the same. It is nice to know there is a new generation of designers emerging out there willing to explore new ideas.

    My 2 cents worth: the additional deck area is a plus for rigging and competitive sailing, but the edges of the wing would be an unsafe location for crew at speed and inconvenient moored - with a tendency to shed unwary guests. The winged hull would likely be difficult to construct using any technique or material.

    For the kind of small boat you are interested in, there are surely better ways of achieving the same end. This hull form is conceived as a fast cruising/racing boat but - as several have already noted - it is probably best suited for flat-water conditions. That is a conundrum: as such, it is clearly intended as a theoretical study and is not envisaged to evolve into a practical vessel.
     
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