Hull series data

Discussion in 'Boat Design' started by anuprdk, May 13, 2018.

  1. TANSL
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    TANSL Senior Member

    This is how I understand the thing :
    DCockey wrote : "the projected planing area is the area enclosed by the chines and transom projected onto a plane parallel to the waterline"
    The figure shows (in red) what you are talking about which is not the planing area. The definitions of the books that you show, yes they are correct, of course.
     

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    Last edited: May 14, 2018
  2. Ad Hoc
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    Ad Hoc Naval Architect

    Oh dear oh dear....same old MO.

    Oh, but wait...

    Yawn...
     
  3. rxcomposite
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    rxcomposite Senior Member

    Tansl- That is the static waterline. For it to generate hydrodynamic lift, the bow rises at a certain speed and the projected PLANING area is a different shape. Common knowledge for those who follow Savitsky theory.
     
  4. TANSL
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    TANSL Senior Member

    RXcomposite, I appreciate that even thinking that I'm wrong, you use a friendlier tone than others. There is no doubt that I have expressed myself badly. I do not say that what is marked in red is the planing area. On the contrary, what I have drawn is what I think Dcokey has defined as a planing area ("The projected planing area is the area enclosed by the chines and transom projected onto a plane parallel to the waterline) and, imo, that is not correct. As you say and I agree, "PLANING area is a different shape". Neither what I have drawn is the static waterline. What I have drawn is the projection on the plane of the static design waterline of the area enclosed by the chines and the transom.
     
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  5. PAR
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    PAR Yacht Designer/Builder

    I think some semantics have come to play here. I agree with TANSL in as much as what is shown in red isn't the planing area, but essentially the water plane or static LWL. The planing area or the "patch", would be somewhat smaller and further aft, though likely a similar shape, given the shape of the hull shown.
    This isn't correct. The patch may be enclosed by the chines, though in very high speed craft, maybe not and the parallel plane to the LWL suggests no trim changes, which is clearly incorrect.
     
  6. tom28571
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    tom28571 Senior Member

    Perhaps TANSL is using the projected area of the boat on its waterline at rest onto a horizontal plane. I'd call that the at rest waterplane and it is what I generally use. Probably depends on what kind of answer your are seeking as chines that lift well above the forward waterline don't come into play unless the boat is running into waves..
     
  7. DCockey
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    DCockey Senior Member

    I think we can all agree that the wetted portion of the bottom when a boat is planing is only part of the area between the chines.

    But that's not what I was talking about in the post #11 which TANSL disagreed with. I was responding to anuprdk's statement "I just dont understand the concept of projecting the planing bottom area, chine" (post #7 above) which is Ap in the context of the Series 62 data which was being discussed. TANSL had previous quoted (post #4) the definition of Ap from the 1963 Series 62 paper: "Ap = projected planing bottom area, excluding area of external spray strips". That definition may be confusing so I provided another definition in post #11 and that is what TANSL disagreed with. In response I quoted two more recent definitions of Ap in posts #14 and #15.

    Ap is not the wetted portion of the bottom when a boat is planing. It is instead a quantity which is used, by itself and in ratios, to characterize planing hull geometry.
     
  8. TANSL
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    TANSL Senior Member

    I see that I still do not explain myself well. Perhaps the attached figure helps to clarify things. Each one can consider as "planing area" what he likes the most. My opinion is that the "planing area" is closer to being that of picture 4, than that of any other picture. I have doubts, only, if the area of sprays generates enough dynamic lift to be considered also within the "planing area".
     

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    Last edited: May 15, 2018
  9. Angélique
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    Angélique aka Angel (only by name)

    Now the last part of your here quoted sentence is not true, in fact it's an outright lie, I've been 100% friendly with you on this thread so far, and have very friendly asked you a question in post #13.
    Point is that you state a posted definition to be not correct, but till now you have carefully avoided to post the in your opinion right definition, while I've so friendly asked for it.

    Nevertheless I'll stay friendly off course, see this as yet another opportunity to post your own definition on the topic, so this matter can be further discussed on these fine and for me educational forums . . :)
     
    Last edited: May 14, 2018
  10. DCockey
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    DCockey Senior Member

    TANSL, you are correct that the area of the bottom which provides dynamic lift when a boat is planing is #4 or possibly #3 in you diagram. However, Ap, "the projected planing bottom area, excluding area of external spray strips", as used in the Series 62 data is #1 in your diagram.
     
    Last edited: May 14, 2018
  11. Angélique
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    Angélique aka Angel (only by name)

    That's not a good idea, since technique is about facts, and not about opinions.
     
  12. TANSL
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    TANSL Senior Member

    @DCockey, what I have written in post # 4 is not a definition of mine but comes from the paper I used to show the shapes of Series 62. (See page 492 in attached paper)
    In any case, whatever I say, this is not correct :
    I don't think so. Maybe someone, who really knows about this topic, can take us out of doubt.
     

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  13. Angélique
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    Angélique aka Angel (only by name)

    So what do you think the right definition should be . . ?
     
  14. Angélique
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    Angélique aka Angel (only by name)

    [​IMG]

    Do you think picture 4 shows a realistic desirable situation, or would you rather like to have the boat more level and the aft end higher on the water, so the planing area would be longer and narrower . . ?
     
    Last edited: May 14, 2018

  15. DCockey
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    DCockey Senior Member

    TANSL, I agree that the definition of Ap you used in post #4 come from that paper. I mentioned it several times. Unfortunately it can be confusing. That is why I provided two other published definitions of Ap including one by Donald Blount, one of the authors of the original paper. Note that in the paper the value of Ap for each model geometry is given in Table 1 on p 494 and is a function of the model geometry only, independent of test conditions (displacement, CG location, speed, etc).

    In Performance by Design Donald Blount discusses the definition of Ap (p 58):

    For an airplane, the projected wing area is of fundamental importance for lift, as the projected bottom area, Ap is the principal source of lift for planing craft. Some designers, however, have argued that the part of Ap forward of each speed's calm-water stagnation line should not be considered as part of design hull loading for calculating the planing area coefficient, Ap/(volume displacement)^1/3.

    This contention assumes the dry forward area does not always contribute to the hydrodynamic lift. This argument, however, ignores the fact that in random waves there are moments of impact when the entire area Ap bounded by the chine and the transom is in contact with the sea.

    Thus Ap defines the total lifting surface available to provide recovery from wave entry, as well as just supporting craft weight when operating in calm water at high speed. The chine and transom boundaries of Ap define the edges of desired flow separation when craft are operating in either calm or rough water.


     
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