Definition of Planing

Discussion in 'Hydrodynamics and Aerodynamics' started by Leo Lazauskas, Nov 2, 2012.

  1. haribo
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    haribo Junior Member

    what are the units for V and LWL?
     
  2. gonzo
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    gonzo Senior Member

    That definition says that very long and narrow hulls plane. The general consensus is that they are not planing since their displacement increases with speed.
     
  3. TANSL
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    TANSL Senior Member

    That definition says precisely the opposite.
    This definition does not mention, at any point, the beam of the boat.
    This definition speech that, for the same speed, the higher the waterline length, the further away the boat planing ability.
    Did not you see the formula or you see but not understand?. If you have time, I'll explain.

    I can not understand this. Please Gonzo, can you explain what you mean?. Speed ​​increases the lift force, this raises the ship and its displacement decreases. Is that what you mean?.Explain, please, because what you say, seems to mean exactly the opposite.
     
  4. Joakim
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    Joakim Senior Member

    That is only true for hull forms that create lift. E.g. a kayak does not and it still can reach those speeds and it does not plane.

    http://www.kayakforum.com/cgi-bin/wiki.pl?Hull_Speed
     
  5. tunnels

    tunnels Previous Member

    AAH BUT HOW DO YOU KNOW ITS NOT PLANNING ??
    HAVE YOU BEEN ON HERE AND SEEN ALL THE SCREEDS OF FIGURES AND FORMULARS AND READ AND ABSORBED ALL THE FERTILIZER ?? YOU COULD BE PLANNING AND NOT EVEN KNOW IT !! SOME ONE HERE WILL HAVE A HIDDEN FORMULAR THAT WILL SAY YES OF NO OR ITS IMPOSSIBLE jUST HAVE TO ASK!!!:(
     
  6. haribo
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    haribo Junior Member

    V / SQR (LWL)> = 5
    the units are LwL[m]; V[kn]
    (I am wondering about the unit kn why not use the dimensionsless unit fn[(L) ..... fn(L)>=0,82....)

    [​IMG][​IMG]

    ninja LwL=10m
    speed V=18kn (average over 500m, not topspeed)
    18 / Sqr(10) = 18 / 3,16= 5,7
    5,7 is > 5 !

    TANSL + tunnels what like you to call this fast sailingboat is doing with his round bilge hull in the water?

    IMO we must ask mr. bernoulli how big will be the difference (or faktor? ) between hydrostatic- and dynamic-lift in this case
     
  7. TANSL
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    TANSL Senior Member

    Haribo, if you will investigate a bit (I see that you do not have time to do), you'd know that the ISO 12215-5 applies only to single-hull vessels. So I can only say: the photos are very nice but you got the wrong site.
    I do not dare to define what is planing, I'm not qualified, but I have my opinion and all I've done is to point an approach taken by the above rule, to qualify a boat, such as displacement or planing.
    I should have stated the units of the variables in the formula, it is true. If the length is given in meters is very likely that the knots are expressed in m / sec. Anyway, the rule explains a lot more than I have explained. Therefore, if anyone is interested, I recommend you read the standard.
    Another question: If you mean by fn froud number, keep in mind that the formula given in the standard is not the number of froud.
     
  8. Joakim
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    Joakim Senior Member

    But it is very much related to Fn, since "hull speed" is Fn=0.4 or V/SQRT(LWL)=2.43 (V knots, LWL meters) or V/SQRT(LWL)=1.34 (V knots, LWL feet) or V/SQRT(LWL)=1.25 (V knots, LWL meters).

    Thus the limit 5 is most likely for knots and meters and corresponds to Fn=0.82. The other two options would give clearly too high Fn.
     
  9. daiquiri
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    daiquiri Engineering and Design

    Gents, are you now discussing and wondering about the units used in ISO 12215?? It's all explained there, it is sufficient to read the text of the standard, page 4. It so clearly says:
    V [knots] = Maximum speed at mLDC
    LWL [m] = Length of the fully loaded waterline at mLDC.

    Regarding the SLR value of 5.0 used in the definition of planing in the ISO 12215, TANSL has forgot to mention the immediately following note, in the same text (page 3):
    "NOTE
    This speed:length ratio limit has been arbitrarily set up in this part of ISO 12215, but it may vary from one boat to another according to hull shape and other parameters."

    So the ISO standard clearly says that it is a rather arbitrary value which depends on various parameters.

    Cheers
     
  10. daiquiri
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    daiquiri Engineering and Design

    Guess it's because kts are so widely used in marine industry, design offices and among boaters that, when someone says "35 kts" we all have an almost "being aboard" feeling of what it means in practical terms, but we don't have the same feel when they say "18 m/s" (which is the same speed). ;)

    Cheers
     
  11. gonzo
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    gonzo Senior Member

    TANSL: On the homepage of your website it states "T.A.N., S.L. is a specialized technical office in the naval sector, directed therefore, to Shipyards, Independent Professionals and other T.O., providing economic solutions, but technologically advanced, to the many problems of this industry". Yet, you continue to say that either you don't understand and then on post #638 " I do not dare to define what is planing, I'm not qualified". Early high speed boats were, this is common knowledge, very narrow. The theory was that narrow, shallow hulls had less resistance, thus higher speed potential. They achieved speeds of 5 or so, but eventually got buried under their bow wave. Unlike wide hulls, they increase displacement instead of decreasing it.
    Tunnels: Are you aware that writing all in caps means you are screaming at us?
     
    Last edited: Mar 23, 2013
  12. TANSL
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    TANSL Senior Member

    Gonzo, thanks for doing me the publicity. Otherwise, I still do not understand many of the things you say. Therefore, and not to enter into new discussions useless, I will not answer you more. Gonzo, thanks for your friendship and for the interest you show for me.
     
  13. haribo
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    haribo Junior Member

    thank you joakim,
    and my apologies for a smal correcture (units after they falls down from the tower of babylon.......)
    V/SQRT(LWL)=1.25 (V meter/second, LWL meters)

    @ daiquiri I learnd the feeling of speed on my bike with a speedometer in km/h and not in knots, but I understand that a kid learning speed on a boat will have a feeling of knots, so for a calculating in your head it will be the best to use the units with your best feelings..... (but sorry, I must transfer your 35kn for me first in ~70km/h than I have a feeling:....much to fast for my smale bike....very danger)

    but for a definition in mathe therms it has exceptional advantages if we use units with build a system together, and as long as speed is distance per time and the LWL a distance why why why not use the same unit for both distances in this smal calculation???
     
  14. daiquiri
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    daiquiri Engineering and Design

    I agree with you. If you saw some of my past posts on this forum, you'd see that I am a big advocate of consistent units (be it SI or British). The conversion of units is always an operation which bears hidden perils, and sometimes leads to long hours wasted in search of the point where the error was made... :rolleyes:

    Cheers
     

  15. gonzo
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    gonzo Senior Member

    I think that planing should be probably defined, if we ever manage to, with dimensionless units. For example waterline length/speed ratio.
     
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