length/beam ratio of around 20

Discussion in 'Multihulls' started by PetterM, Apr 21, 2015.

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  1. Mr Efficiency
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    Mr Efficiency Senior Member

    Why make a smart-alec remark like that ? The bloke asked for a reference, because none was given.
     
  2. Mr Efficiency
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    Mr Efficiency Senior Member

    You don't improve, do you ? Insufferable, uncharitable, overbearing, and just plain arrogant. Don't think you're improving traffic on this site old mate, but keep up the good work and you might get rid of a few more !
     
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  3. Leo Lazauskas
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    Leo Lazauskas Senior Member

    And he got one. (I wasn't replying to any one person, btw.)
     
  4. Mr Efficiency
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    Mr Efficiency Senior Member

    What's the " zany, novel idea" ? Looking for, and ploughing through, original research papers ourselves, instead of being lazy and asking questions of The Oracle ? Not much point in the forum if that is the case.
     
  5. Mr Efficiency
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    Mr Efficiency Senior Member

    "useless" is the single-word comment to give me some negative rep, don't be shy, come out here and show yourself Mr Anonymous ! ;) I am starting to think that epithet could have considerable application around here. And knock off as much rep points as you like, I couldn't care less. :cool:
     
  6. Ad Hoc
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    Ad Hoc Naval Architect

  7. Mr Efficiency
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    Mr Efficiency Senior Member

  8. Mr Efficiency
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    Mr Efficiency Senior Member

    talking about "useless", post #33 here gets my vote !
     
  9. Mr Efficiency
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    Mr Efficiency Senior Member

    "Well, if that means one less charlatan sprouting religious mysticism subverted for engineering, great "

    well ? do explain ! ;)
     
  10. daiquiri
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    daiquiri Engineering and Design

    How about getting back to discussion about boats?
     
  11. Mr Efficiency
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    Mr Efficiency Senior Member

    God bless you daiquiri, whoops, that sounds like someone sp(r)outing religion ! :D
     
  12. Mr Efficiency
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    Mr Efficiency Senior Member

    I'd prefer to talk about the boats, but whoever deducted some of those precious little rep points with this gem......Find somewhere else to thump your bible.....seems to have other pre-occupations ! I wonder who that could have been.....:D
     
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  13. hump101
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    hump101 Senior Member

    I just ignore the snide comments in the hope that I might still learn something useful, so I appreciate your comments on my behalf, Mr. E., but don't worry about my sensibilities!

    Thanks for the reference. I had thought the curves looked like Molland et al. These are made using NPL round bilge naval vessel hullforms, nothing like a modern catamaran, and the authors acknowledge the issues with this, but were correlating with earlier studies they had done with the same hull form.

    This is definitely not a monohull split down the middle, so that interpretation is wrong. It is as I described, with two identical hulls, each with the same displacement as the mono, with the total resistance of the cat halved for the graph. I watched some of those tests being done, so I can vouch for that.

    I've done some work on "split mono" cat forms, offshore racing powerboats, and I've built a 12m power cat with asymmetric hulls (though not fully flat on the inner faces), so I've got a bit of experience with this. The 12m boat design was tested at 1/10th scale, and we found that the resistence of an individual hull correlates well between model and full scale, but the resistance of the catamarans did not correlate well, with the model generally over-predicting the resistance. In the model there were several humps and troughs at different speeds associated with waves interacting in different ways. At full scale, the catamaran shows a resistance which is practically the same as two monohulls, except for one small hump in the curve in a narrow speed range, which can be observed as a peak between the hulls which touches the bridge deck. Had the inner surfaces been completely flat, then I had hypothesised this small difference would be eliminated, as I've not observed a similar peak in the race boats, but I've never seen any data to confirm this hypothesis. The B/L for this boat is 0.375, with hull spacing/L equal to 0.275.

    I have found this issue to be really interesting, as I spent a lot of effort refining the 12m design to improve the wave resistance basd on the model tests, only to find at full scale the wave resistance was not so critical. I had compromised the frictional resistance to achieve this, so was pretty frustrated, to say the least! I intend to repeat the experiment with my F40 hulls (symmetric) as I suspect that the increase in frictional resistance was more than the reduction in wave making resistance at full scale.

    I'm not a hydrodynamicist, so can't explain why this scaling of wave interaction seems to be such an issue, hence my questions here to those more knowledgeable than me.
     
  14. Mr Efficiency
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    Mr Efficiency Senior Member

    Interesting comments, hump101, and well explained, but my theoretical predictor says they won't be well received by the Lord Warden of the Catamaran !
     

  15. yofish

    yofish Previous Member

    You know Mr E, I like you more all the time. Now, let's introduce some building methods to complete the decent into lunacy.
     
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