Definition of Planing

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

  1. Stephen Ditmore
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    Stephen Ditmore Senior Member

    Eugene Clements draws a parallel between planing hulls and supercavitating foils (e.g. supercavitating props).
     
  2. Stephen Ditmore
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    Stephen Ditmore Senior Member

    Directing your attention to page 22 of this thread, can Savitsky's definition be used to recalibrate the Almeter Number that defines planing?
    (Almeter puts it at a point that strikes me as overly fast).

    As I asked on that earlier page:
     
  3. haribo
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    haribo Junior Member

    sorry, yet I am not in the position to understand almeterĀ“s or clements intention with his numbers....

    but I understand now that we have to look to the changes in the flow (changes of the pressure field) between displacment and planing and not so much to the (relativ-)speed

    the relativ speed for the change of the flow is IMO a criterium of the efficence of the planinghull, a hull that starts to plan with lower relativ speed seems to be more efficient...., but not so much a criterium for the definition of planing itself
     
  4. HJS
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    HJS Member

    Definition?

    What is the definition of a definition?
    What is the ultimate purpose of a definition?


    js
     
  5. rxcomposite
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    rxcomposite Senior Member

    That would be too difficult. Even the scientist could not agree on what is NOTHING. Even zero has a definition, beyond zero or nothing is what the scientist could not agree on to define.
     
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  6. gonzo
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    gonzo Senior Member

    The ultimate purpose of a definition is to allow people to create limits for a description. It prevents apparent disagreements. For example, arguing about two different things called by the same name. Otherwise, arguing about because of calling the same thing by different names. It is the basis of science, philosophy and Human knowledge in general.
     
  7. philSweet
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    philSweet Senior Member

    Okay, I think quite a lot of the folks involved in this discussion have gravitated towards estimating the components of hull pressure. One difficulty with that is that the wetted surface can be assumed to be very different, and even the waterline does not reflect sea level in any useable way. It also isn't obvious to me why the ITTC would go for it. The point of a specification is to produce an economical and adequate gadget. Planing ought to relate to some tangible component of business in a very clear way if it is to receive a lot of attention in the test and validation of the deliverable.

    At least one person mentioned sinkage. And several more have mentioned VCB requirements. The single simplest definition that I can think of is to say a boat is planing when its sinkage stops increasing. Specifically, the speed which for all faster speeds, the VCB is above its minimum.

    In my mind, this definition has several desirable features.

    1. It requires nothing new in the way of describing a vessel's behavior in general- sinkage being a customary metric already.

    2. I suspect the test tank people can adapt to it fairly easily as far as equating models to actual ships if it turns up in specifications.

    3. It does not temp specifiers into overly simplistic contractual wording by just saying "Shall plane at 20 knots" etc. That would fall well short of giving everybody what they wanted, which no single definition is ever going to do. However, it might also be why nobody will like this definition.:D

    4. It works on pretty much any hull. For a multihull or asymmetric hull, you would have to specify heel angle.

    5. It doesn't lose relevance in a seaway.

    6. It admits hull appendages and control systems and all varieties of set up.

    7. The fact that previous vessels and models can be analyzed with respect to this definition provides a graceful entrance. I hate it when a new species of specification can't be evaluated with previous data to get a feel for the critter. That requires proceeding very gingerly.

    Its downside is that it may not be a strong enough definition to be of any real use. It may also suffer from the fact that a boat could have a very long, flat sinkage response. This could make the testing and acceptance condition dependant on more than just this one condition. Generally speaking, you want to test for requirements one for one. But that doesn't always work. Try comparing the performance of two bulldozers tested a thousand miles apart. Snowblowers are fun to write acceptance tests for also. It never snows per specifications. Sometimes, it doesn't snow at all, even in Marquette Michigan in December. Regardless, at some point, you have to man up and make a damned decision. Would this definition of planing help you do that? Does it lend itself to contractual language that can withstand legal scrutiny. Do you end up with a better boat for your money?
     
  8. tunnels

    tunnels Previous Member

    Its like these posts no one can agree with anyone else when a poat is planning !!
    Want to know a secret ?? i know when my boat is planing and im not telling anyone !!
     
  9. gonzo
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    gonzo Senior Member

    Tunnels: You have been very disruptive. If you have nothing but sarcasm to contribute, please stay off.
     
  10. tunnels

    tunnels Previous Member

    What a dull boring life some people lead !!

    How can anyone disupt someything thats going no where !!
    Is there no such thing as a yes or no answer or just a million shades of might be and maybe or it could be but then again it might not be !
    All any one can contribute is information and formulars develope from the dim dark ages !! :mad:.
    Is everyone lazy ? or hasent any one done any modern day up to date testing and research in this day and age of super duper computers to produced one single solution to say that boat is planning when bla bla bla !! :eek:
     
  11. gonzo
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    gonzo Senior Member

    Tunnels; I think that you should show good manners and delete your insulting posts.
     
  12. tunnels

    tunnels Previous Member

    Insulting in what way ??
    what is insulting in speaking the truth ??
    no one can agree with anyone else ,everyone has had there say and no one agrees with any one else !!
    Me as a person searching for answers in simple language after reading a dozen posts can see its going round and round on ever diminishing circals !!
    Insults i have seen worse things written in little kids story books !!
    Why is everyone refering to formulars and papers that must have first been written on stone with a chisel ,the information is so old !!
    Is there no modern simple yes or no answers ?? information that with the push of a button on either of my two computers i can get an answer ??
    I want you to tell me when my boat shows indications of when its planning !! keep it simple because my chisel needs sharpening and the stone man wont be here till this afternoon !!! :(:rolleyes:
    After 672 posts and still no further ahead than the second posting !
     
  13. haribo
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    haribo Junior Member

    I agree with you!

    but is it nessesery that I agree with you? is it a democratic question? if 99% agree with whatever it could be wrong

    you know when your boat is planing! as every millon of surfers know when their boards are planing down the wave, they can not surf without planing and they know if they surf, so they know that they are in planingplaningplaning modus

    for your other question (is there no simple yes or no?) the adequat answer is "there is no simple answer" even the clever second poster wrote it:
    "First, my personal opinion is that such a definition needs to be completely quantifiable" (Don MacPherson) .......... not only yes and no

    and if you read his post again, you will found out that his idee is clever first snapshot idee "It is planing if the dynamic VCG is higher than the static VCG." is not suitable for a single surfer on his board, planing truly down the wave, it is not suitable because you and me we can not deside if the CG of a planing surfer is climb higher or deeper if he start his ride, it will climb up and down with the waves rolling under him if he do not start.. and it will stay at one high (or fall down a little bit???) if he start.....

    you are correct if you say: a thinker can not come up with the idee to surf down a wave, and a surfer can do it but can not explain it,

    but neither the conclusion: stopp thinking go surfing!
    nor the conclusion: stop surfing start thinking!
    is correct for any man

    the surfer create the idee of surfing, and the thinker might gave him back a definition of a better board, it alternates between experience and passion, between theorie and skill

    what is wrong if we think a longer time over a problem? is it not fabulous that we can sit around the world and wrote 6XX posts over one question?

    for me and others there is a lot to learn (not only the language......), nothing for you? I promise you, if we found out a definition after post 6666, you could build a beautiful better boat like is your passion

    (by the way did you found a new job??)
     
  14. Dave T
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    Dave T Senior Member

    Dave T's simple definition of planing

    Since I know very little about hydrodynamics or other technical stuff I'll give you my own definition of planing. To me planing is the reduction of displacement as speed increases and is influenced by the shape of the hull, the weight of the boat, weight distribution and the amount of horse power applied. So I would define planing as a percentage, a boat at 50% plane would have reduced the volume of water it displaced setting still by half, at 100% plane the boat would no longer be displacing any water and would actually be flying. So anywhere in between and the boat is planing to a certain degree.

    Adjusting planing attitude. Slow speed leaving dock or in no wake zone. Wife and large cooler of beer in back of boat bow raised. Medium speed have wife move to middle of boat and bring cooler with her. High speed have wife move to front of boat and adjust beer cooler as needed to level boat. As beer is consumed and waist products are disposed of over railing reduce speed.

    Dave T :cool:
     
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  15. daiquiri
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    daiquiri Engineering and Design

    Hi Dave
    More or less we have all agreed that the base of the definition of planing should be the fact that, as speed increases, the hydrodynamic force takes over an increasing part of the vertical load, and at the hydrostatic force decreases by the same amount.
    The part nobody could agree on so far concerns the quantitative part of the definition. How much of the hydrodynamic force is enough to declare the hull on plane?
    By the way, 100% hydrodynamic and 0% hydrostatic force is physically impossible condition because, as you have noted, the hull would then be flying, and hence not planing. ;)

    Good one. Would like to hear your wife's opinion on this regard. ;) :p

    Cheers
     
    Last edited: Apr 4, 2013
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