rhino unroll prob's!?

Discussion in 'Software' started by tugboat, Sep 20, 2013.

  1. DCockey
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    DCockey Senior Member

    That's considerably more complicated than how I work in Rhino for hulls with developable surfaces. :eek:

    A basic method for creating a developable surface hull in Rhino:

    1) Create sheer, chine and keel curves in 3D. the keel curve and the chine curve should coincide at the stem. Either start by drawing the curves in side-view and plan-view, or draw directly in 3D. Adjust the curves until they are as desired. Rebuild the curves with the minimum number of points which give the desired shapes. It's preferred but not required that the sheer, chine and keel curves have the same number of points. Typically 6 to 15 should be satisfactory.

    2) Create the side surface with the Loft command, Developable option using the sheer and chine curves. If the first attempt is not satisfactory try selecting sheer and chine curves a different location. Typically selecting both around amidships is satisfactory. If the surface is still unsatisfactory the shape of the sheer or chine curve may need to be modified.

    3) Adjust the shape of the keel curve so that it aligns with the stem end of the side surface if desired.

    4) Create the bottom surface with the Loft command, Developable option using the chine and keel curves. If the first attempt is not satisfactory try selecting chine and keel curves a different location. Typically selecting both around amidships is satisfactory. If the surface is still unsatisfactory the shape of the chine or keel curve may need to be modified.

    5) Create the transom using the edges of the side and bottom panels. Note that the edges of the created side and bottom panels define the edges of the transom.
     
  2. tugboat

    tugboat Previous Member

    but if it was created as you described (which was how I also initially created my surfaces)in your last post to monsieur Watson-
    then wouldn't it be able to be created as I intended? since it seems others at rhino have pointed to my unfair lines as the culprit. it seems fairing the lines must have some effect on the compound curvature in making it less compound? please explain further on that?
     
  3. bhnautika
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    bhnautika Senior Member

    Here is another idea to remove some curvature from the bow. I used the original file, took the lines off those surfaces then rebuilt to 10 points did some small adjustments to smooth some points, extended the keel line and moved the chine and sheer line end point out from the centre line at the stem. I created the surfaces then using the forefoot curve trimmed the surfaces at that point. You then model the stem as separate surfaces which can be unrolled. I put in a few section lines to show the result (blue lines top model) also a straight line between the end points to show the difference.
    (green).
     

    Attached Files:

  4. DCockey
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    DCockey Senior Member

    The bottom of the upper hull has considerable compound curvature though it still unrolls. Whether it is "close enough" to a true developable surface for tugboat's purposes depends on how the material he uses behaves, his fabrication methods, and how directly and accurately he expects to go from the Rhino model to the physical build. Some experimentation with a scale model may be useful and informative.
     
  5. bhnautika
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    bhnautika Senior Member

    My suggestion for the bow was to help improve on this.
     

    Attached Files:

  6. tugboat

    tugboat Previous Member

    thanks bhnautika, seems im no the only one with developing issues- your hull is out a whopping 0.21% per sq ft. I do appreciate the help...im wondering If the chine is too high?
     
  7. tugboat

    tugboat Previous Member

    Dcockey- im wondering if the chine is too high toward the bow? meaning the vessel would tend to squat?

    also it would not trim properly...might have to go for a redesign and try again...but this is about as simple as it gets and if rhino cant give me good tolerances and/or if I don't have the skills to draft it properly- then it is "stock plans time" for me...
    might just go with a stock glen-l tug- which has flared sides- although Im guessing that has some advantages- I could just use some good fendering to fill in the flare and make the vessel able to tow on the hip better...im thinking aloud here...

    suggestions?
     
  8. DCockey
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    DCockey Senior Member

    Remember that a developable surface will probably have curved transverse sections. The surfaces I provided in post #21 are very close to exactly developable, and the bottom has curved transverse sections near the bow. I'll attach it as a Rhino 4 file with transverse sections added.

    The curvature of the transverse sections in the bow can be reduced but it will require carefully tailored changes to the keel and/or chine curves to keep the surface developable.
     

    Attached Files:

  9. DCockey
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    DCockey Senior Member

    Rhino can provide surfaces and unrolled shapes which are as close to exactly developable as anyone needs. But to achieve that with the type of shape you want may require considerable experimentation and patience. Understanding how developable surfaces work and the relationship between the defining curves and the resulting shape takes a lot of time. including study to understand how developable surfaces. It can be considerably more work to design a developable hull with the desired work than a round bottom hull.

    There is a lot to be gained by going with a set of proven plans. The Glen-L Fred Murphy does have vertical bulwarks.

    I would expect the shape of the stern would have considerably more effect on squatting than the shape of the bow.
     
  10. bhnautika
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    bhnautika Senior Member

    Tugboat that was from your original hull, I only smoothed the lines a little to move the bow end out to show a possible way of reducing the curvature in the forward sections.
    "whopping 0.21% per sq ft" ?
     
    Last edited: Sep 24, 2013
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  11. baeckmo
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    baeckmo Hydrodynamics

    In one of his previous comments above, Tugboat seems to have made a mistake in calculating the resulting area difference. His values are 100 times too high, since he is multiplying with the percentage factor (i.e. 0.21 instead of 0.0021).

    In the case at hand, this surplus area corresponds to a circular patch of 0.62 in (15.8 mm). Whether that is whopping or not, is a question of what material you use, something that David has noted on several occasions now!
     
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  12. tugboat

    tugboat Previous Member

    Yea-my apologies it looks like I actrually miscalculated...I thought that means that 1 sq ft = 144 sq inches- and that the plate is 21% larger when unrolled or 30.24 sq inches bigger- it seems quite large.

    sadly those are the stats im getting too...I managed to get it down to .03% and Dcockey-who is turning out to be a very gifted draftsman- managed to get it to "within tolerance"...which I think is .0001% or something ridiculously envious ! I hope I didn't come across as being arrogant and apologize for any misunderstanding- I was actually making a joke at my own lines...no foul intended.

    btw thanks for you attempt- its been a tough road. I think im done with the -diy-design-a-boat-yourself-without-a-naval-architects-training-method.
    :):):)
     
  13. tugboat

    tugboat Previous Member

    Jeezuz!!! am I that out?

    my mistake...sorry guys. yea that would make more sense...but isn't 0.21 a percentage of 21% when applied to a sq ft? I guess im eating my foot for dinner...
     
  14. tugboat

    tugboat Previous Member

    the stern does in fact have a lot to do with a squat- however a bow section that is too buoyant would also affect it. at least from my understanding?

    the only issue with a stock plan is- Im making a couple big compromises by going with a stock plan.

    i.e. I would be building a tugboat with my own hypocritical "don'ts" on a tugboat...which are fared sides. and it limits my steam dream.

    I might be able to get a water tube boiler in her but forget a HFT boiler. or a VFT either. too much weight and or not enough room. But it has other advantages.

    Its not a true tug but it can do the work I need to do- im not building a commercial vessel. the compromise is - its a steel boat- its a proven design -it has accommodations layed out, it is good in heavy weather, economical to run, and it does look nice. easy to build - cheap to build. etc...

    I loved my design though. but some things must remain a dream-- better to get out on the water sooner...at least I think.
     

  15. tugboat

    tugboat Previous Member

    this is totally from my understanding and I could be quite mistaken here-

    when the hulls chines are too far out of the water- which I believe mine to be- they force the vessel to try and plane even though the hull is not a planing type- in doing so it rides higher on its bow wave, due to the buoyancy of the a fuller and deeper forefoot.
    thus forcing the aft sections downwards. a strong engine and a offset shaft might counter this. since the force of the prop would be vectoring through a spot aft of the LCb(I think) countering that tendency to squat- but the bow does not help if it is too buoyant from my understanding. a buoyant stern is a huge percentage of what stop the squat in a tow. something you don't want. so all I know is-
    to me something doesn't look right at the chine as well. Not just the unrolling of the hulls...as Dcockey has said I think this might require a lot of tailoring...?
     
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