Need Rhino help with hull surface from curves

Discussion in 'Software' started by zmrbill, Jul 22, 2014.

  1. zmrbill
    Joined: Jul 2014
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    Location: San Diego

    zmrbill New Member

    Hi,

    I have a sof row boat design that I started with in delftship and have been adding frames etc. I am having trouble producing a hull surface from open curves that define the transom, keel, edges and chines. I will post the file and would appreciate some help producing a surface for the hull.

    Thanks in advance, Bill
     

    Attached Files:

    Last edited: Jul 22, 2014
  2. DCockey
    Joined: Oct 2009
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    DCockey Senior Member

    Attached is a first pass at a surface.

    Input 1 has the curves I used.
    Stem: rebuilt using FitCrv
    Keel: rebuilt the two curves into one and faired slightly

    NetworkSrf Surface has a surface created using the curves in Input 1

    Rebuilt Surface is above surface rebuilt and simplified using FitSrf

    Keep in mind that a NURBS surface is a rectangle in UV parameter space. Think of it as starting as a rectangular rubber sheet which is then bent and twisted into the desired shape.
     

    Attached Files:

  3. zmrbill
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    zmrbill New Member

    Hey thanks David,

    I see a bulge in the center of the bottom as meets the keel. Any idea how to rectify this?

    Thanks, Bill
     

    Attached Files:

  4. DCockey
    Joined: Oct 2009
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    DCockey Senior Member

    Several possibilities for dealing with the bulge:

    The most obvious but perhaps the most frustrating would be to directly edit the current surface's control points.

    A fundamental question: how close does the Rhino surface need to follow the DelftShip surface? If closely then you could export more data from DelftShip such as section curves and/or mesh vertices and use that data to create the surface in Rhino which is a close match to the DelftShip surface. I've done that once or twice in the distant past but don't remember the details. Others should be able to provide help. However, the curves you did export show that the DelftShip surface could use some fairing.

    If not so close then another option would be to export more data from DelftShip such as section curves and/or mesh vertices, and use that data to create a simpler starting surface in Rhino, and then edit and fair that surface. The result would deviate from DelftShip surface which could checked using the PointSetDeviation command in Rhino.

    Another possibility would be create several section curves in Rhino using the curves you have, and then use those section curves and the current curves to build a simplified starting surface in Rhino. The starting surface could then be edited and faired.

    And there are more alternatives.

    What are your objectives?
     
  5. rwatson
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    rwatson Senior Member

    You have a lot more problems than that.

    For a SOF boat, you cant have hollow 'cheeks' in you stem, as the fabric will 'fall off' it.

    Also, the rest of the hull is all 'kinky'.


    Try generating the hull again with fewer frames and chines
     

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  6. DCockey
    Joined: Oct 2009
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    DCockey Senior Member

    I missed that it's a skin-on frame boat.
     
  7. SukiSolo
    Joined: Dec 2012
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    SukiSolo Senior Member

    Might also be worth considering 'How to build' as this may have a bearing on the moulds, stringers and rib configuration. I put a couple of links below to show different approaches to this. Personally I have only built SOF canoes, the old PVC covered types, once very popular here in the UK. These used primarily stringers to form the material around.

    http://gentrycustomboats.com/whitehall page.html

    http://www.capefalconkayak.com/adirondackguideboat.html

    Your decision on build method may influence, how you approach modelling the hull which is why I mention this. Effectively you need a developable surface to get the material to sit correctly. It is almost like thin ply, so do not assume it will stretch unless you have a bias cloth which will do so, until resin impregnated.
    Or you could use polythene and 'shrink wrap'..;)
     
  8. zmrbill
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    zmrbill New Member

    Wow, thanks so much guys...

    Some background...I live in San Diego within minutes of the bay and ocean(see picture below). I owned a Hobie 16 in my 20's and now in my 50's I want to take advantage of my location and get back out on the water. I want to start rowing for exerciser thus the SOF row boat. So the boat will be a car top, 1 person skull, 2 person fishing with trolling motor and possibly sail in the future. I may do some fun transits like San Diego bay out to ocean and back into mission bay. Target weight is < 70 lbs. I will be using spruce, plywood and polyester.

    As far as this design it is heavily based on Dave Gentry's whitehall. I found a modified version of this at:

    http://andrewlinn.com/whitehall/111006_background.htm

    From this website I was able to get an idea of the skin on frame design. Also John Brown's youtube videos gave me encouragement.

    Starting from scratch I bootstrapped myself on defltship and rhino. The design started out as a 13 ' in defltship shell that I dxf'd to rhino. With the design in rhino I added the frames, stringers and stretched to 14' that I am now trying to produce a surface from. I have also started on a model of this design at 1/5 scale(picture below). The curves I'm using to build a surface on are curves run through the frames Having a surface in rhino is a learning goal for me and I wanted to check displacement at different loads.

    So I hope that provides some background on where I'm coming from and where I'm headed. Thanks so much for your interest.

    Bill
     

    Attached Files:

  9. rwatson
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    rwatson Senior Member

    You can see from the photo of the part finished frame that there are no "hollow" sections in the design.

    Sukis comments are very pertinent. You couldnt use a heavy canvas on that frame, as its not developable.

    However, you could use something like ballistic Nylon or heavy cotton "duck", which can be comfortable stretched in several directions.

    My dear old dad showed me how to use a small bit of timber rolled up in the selvedge to roll and tighten the material around the gunnel.

    Its the same technique that upholsterers use.

    Or you can use a special tool - if you can be bothered watching all the building process, like this guy

    https://www.youtube.com/watch?v=H5tApIe58GE
     
  10. SukiSolo
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    SukiSolo Senior Member

    I quite like the look of those Whitehalls, similar in some ways to the Thames rowing skiffs, again developed over many years.

    There is often no single 'right' way some times to build a hull surface in Rhino, so be prepared to try different techniques. Don't get frustrated, or when you do, try a different approach. Best thing is to keep lines, curves etc simple, same with surfaces. The simpler the basic surface, the better it is and 'sweeter'.

    Rhino will give some basic Hydrostatics but you ned a little bit more to ensure you have a sweet shape at differing displacement. Primarily I would suggest examining the curve of areas. Worth plotting as a graph so you can visualise it. Use 'construction' surfaces to help obtain the necessary values. You can go the other way and input your section curves from points - see inputting a *.csv file in Rhino Help.

    Nice thing is you should and will be able to develop the surface. A minute deviation will not be important in the real world, say 0.5% off. Of course it will then give you the flat sheet of material you will need to skin the frames with.
     

  11. mazz
    Joined: Sep 2012
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    Location: Malta

    mazz New Member

    Need Rhino help with hull surface from curves using background images

    Hi guyz,

    I am currently on a self-learning mode using rhino. And so far, I think it is one of the best, if not the best software programs for hull design, even though I am still at a beginners stage.

    However, with this particular design I am having problems to be able to close the bow stem when trying to use loft.

    Maybe someone can help me in this area please?

    To better visualize I am attaching the .3dm file.

    Your feedback would be very much appreciated.

    Thanks,
    Mark
     

    Attached Files:

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