Gerr's Roll Period Recommendation

Discussion in 'Stability' started by DCockey, Jun 20, 2011.

  1. Alik
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    Alik Senior Member

    Grant, are You familiar with ship dynamics? For me, it is main degree. I do not need You or others consider my thoughts same weights with Dave, there are facts - You are free to believe or not. All information is presented, references are made. And also pls note that criticism is normal for scientific discussion.

    P.S. OK, just found You are Westlawn student about to complete the course. Well, backing up Your teacher is good move.
    Quick test: can You tell us, without looking to Google, what is residual resistance?
     
  2. BMcF
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    BMcF Senior Member

    So you have applied that degree to the actual testing, data reduction, correlation and development of predictive methods on how many real ships and/or tow tank models?

    Just curious. I've worked with many folks who hold advanced degrees in ship dynamics and similar. And I've worked with many more who do not have a directly related degree but who have amassed a lot of practical knowledge over the 40 or 50 years that they worked with advanced marine vehicle design.
     
  3. Alik
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    Alik Senior Member

    Just curious: would You ask Dave to post his CV as well?
     
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  4. BMcF
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    BMcF Senior Member

    I already know his from working in this field for as long as I have, from using his publications for references and from crossing his (or his student's) path on occasion as will often happen in the ship and craft design world. Heck, the last conference I attended just weeks ago (MACC) was like some sort of "old guys that been designing advanced craft for the last 50 years" reunion. We all joked about that...except for the getting old part.:rolleyes:


    Perhaps you've been around longer and done more; that's fine and good on ya. I said I was just curious. I certainly don't claim that I know everyone in this funny business I chose and I certainly doubt that many know me either, so I tend to back up my assertions with a bit of "CV" when trying to drive home a point that gets contentious. Just a bit though.....:D
     
  5. Alik
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    Alik Senior Member

    Again, it is not about who is longer in the business; it is all about scientific facts. Do You have anything particular to say about equation of roll?

    For C.V. just follow link at profile.
     
  6. BMcF
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    BMcF Senior Member

    Nothing to add other than that I use other 'equations of roll' since most of the vessels I work with are multi-hulls. ;)
     
  7. BMcF
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    BMcF Senior Member

    So how do you explain then that so many of the best tools and methods that have been employed so successfully for so long are emperically based.?
     
  8. BMcF
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    BMcF Senior Member

    Did. Nuff said.

    Carry on.
     
  9. Alik
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    Alik Senior Member

    Most of classic ship hydrodynamics is empirical... But behind that, the empirical model should be correct and match physics of phenomena omitting negligible factors. The question is what level of simplification is acceptable?

    Talking about empirical formulas - all of them have their limitations and conditions of use that should be clearly specified. Unfortunately not always...

    Enclose extract from Russian small craft design reference book (often used by me), this section includes discussion of approximate performance prediction methods. I understand You can't read it, but it is easy to note that for every formula/method limitations are specified, and for some formulas accuracy is specified also. And the section starts from discussion of limitations. This is good style of presenting such formulas that is unfortunately not seen in SOME popular books. So this is source of problem.
     

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    Last edited: Jun 28, 2011
  10. daiquiri
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    daiquiri Engineering and Design

    What does "advanced craft" mean?
     
  11. BMcF
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    BMcF Senior Member

    I use that term loosely as it fell out of the old USN "Advanced Marine Vehicles" terminology of the day. It meant, then, just about anything that was not a conventional displacement monohull and falling just about anywhere on any leg of the 'famous' sustention triangle whose corners were defined by powered lift (ACV/SES), planing lift, and foil lift.

    The SWATH came to be lumped in the AMV world too and since the origin of the term AMV, there have been some 3,4 and 5-hull multihull concepts show up that fit in that box.

    Today..it's meaning has not changed much although the number of what were then 'advanced technology' craft are much more commonplace now, of course. That said, hybrid combinations that fall on the legs of the sustention triangle are still popping up to this day. Our last hybrid project, for example, combined pure hydrofoil technology, with 1800s Herreshof super-slender monohull technology, topped off with trimaran amas to keep it upright whe off foils.

    The term "HPMV', or High Performance Marine Vehicle, is what is now in vogue, it seems, but I'm stuck in the past. I still call Air Cushion Catamarans SES', for example.
     
  12. Grant Nelson
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    Grant Nelson Senior Member

    Check this out, http://www.gerrmarine.com/dave.html no need to ask...

    however I could not find yours next to a short paragraph on your website (and even then I dont know if that is you, since I do not know what your real name is).. for the rest its all pictures, can not even read the articles you post, etc... you must have a list of your 60 scientific articles (and no, I will not ask Dave for his since I have seen and read enough, and read other peoples reviews of his work, to be able to judge his skills.

    And WOW, do I wish I was about to graduate from Westlawn, and BOY do I wish I could brown nose Dave, but alas, for me that is not in my nature, as Dave and others can tell you.. heheh..

    Regardless, I am sure this thread has greatly improved your reputation with potential clients, which would be no different...

    Anyways, happy fishing, you hooked me, but now I am going to break the line and let you go for bigger bait...

    Grant
     
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  13. BMcF
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    BMcF Senior Member

    I didn't either, but I saw the collection of little boat pictures and realized we worked in very different areas of marine design..although some of our free-running models are about the same size.:D In fact, the last we built was 17m LOA..a ~1/20-scale model of a 50-knot 340m LOA fast ocean transit vessel.

    It's all good; a lot of those small craft looked very nice.
     
  14. Ad Hoc
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    Ad Hoc Naval Architect

    But we know the quality of your work :)
     

  15. Alik
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    Alik Senior Member

    Gerr has no degree in naval architecture or related field. That's enough for me to not involve in further comparison of qualifications.

    Unfortunately question to Grant on residual resistance remain unanswered. So I made my conclusions :cool:
     
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