17ft aluminium center console boat - Opinions?

Discussion in 'Boat Design' started by Maxxi, Apr 10, 2019.

  1. Maxxi
    Joined: Apr 2019
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    Maxxi Junior Member

    Hello! Just registered to this forum, and would appreciate your thoughts about my boat build idea. I was modelling an 17ft boat(hull) with Freeship, but I really don't have any experience of boat modelling. I would really appreciate your opinions and viewpoint about the model. What do you think about it? Is there something that looks badly wrong?

    Boat size is 17x6.9ft with an 15 degree deadrise. It would be an center console boat with an 40-80hp outboard, and as light as possible. Usage mostly as a fishing boat that would be usable on lakes but also in the sea. Material thickness 4mm aluminium for the bottom and the sides, 3-4mm for framework and deck builds, 5mm for the transom. I can source aluminium plates and other materials. Cutting and welding isn't an issue. Really have had a lots of thought about this build, but of course it would be quite a lot of work.

    alu_boat_project_02.jpg

    alu_boat_project_01.jpg

    alu_boat_project_03.jpg

    alu_boat_project_04.jpg
    alu_boat_project_05.jpg
     
  2. Mr Efficiency
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    Mr Efficiency Senior Member

    Similar to a recent thread, your boat is drawn with straight sections, and your plating will not conform to those. Have you checked the design for developability, on your software ?
     
  3. Maxxi
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    Maxxi Junior Member

    Ok, thanks for your concern, but, hmm, I don't follow..? Freeship can layout the shapes to developable surfaces and export to DXF that I can nest to a laser cutter program. All parts can be cut out from flat sheet.

    boat_dxf.jpg
     
  4. Mr Efficiency
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    Mr Efficiency Senior Member

  5. JSL
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    JSL Senior Member

    Mr Efficiency is right. Straight frames (as on your 'body plan')= non developed. One exception is using canted frames and that is much more difficult.
    I assume the body plan (illustration on the left, viewed from stern?) is the aft portion of hull???? Unless I am reading it wrong, the deadrise appears to increase & the hull tapers (comes in at the stern).
    You might want to consider a chine 'flat' - a better, drier ride plus many other advantages
     
  6. Dejay
    Joined: Mar 2018
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    Dejay Senior Newbie

    Delftship free and I think freeship too has an option to mark what surfaces are developable (alt-D)
     
  7. Maxxi
    Joined: Apr 2019
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    Maxxi Junior Member

    You guys got me really confused. What else form could be done with sheet material than a hull with stright sections? You can't do any curvation in the vertical axis, but twisting and bending isn't a problem. What would you do with the developable surfaces feature if it's not calculating the cuttable sheet form?
     
  8. Maxxi
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    Maxxi Junior Member

    In fact so confused I had to cut parts in 1:10 size of 2mm steel sheet and tack them together. And I can't see a problem here..? o_O

    IMG_20190410_204632.jpg

    IMG_20190410_204713.jpg


    Edit.

    The hull deadrise is fixed 15 degrees for about 1,8 meters from the transom, then it starts to steepen. Also in the final build there would be lifting strakes and chine rails.
     
    Last edited: Apr 10, 2019
  9. Dejay
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    Dejay Senior Newbie

    Did you check for the "developable surface" option in freeship / delftship? Maybe you don't have a problem :) It should be easy to check and see if you can just nudge a few vertices around to fix it.

    I don't quite understand developable surfaces myself. It's confusing. I have no experience metalworking. But it's possible that problems crop up with larger or thicker sheets. Clearly your model is at least "almost developable", but your model does look a bit "tortured" in parts. Might work fine.

    If you look up ruled surface: "In geometry, a surface S is ruled (also called a scroll) if through every point of S there is a straight line that lies on S" (put a ruler on the surface).
    All developable surfaces are ruled surfaces but not vice versa!

    Best way I can imagine it is if you have a straight line and a wavy curve and connect those two with straight lines to make a surface. It's easy to imagine that if the wavy line is extremely wavy that you couldn't make that shape out of a sheet without compressing or stretching the sheet. Try doing it with a piece of paper while keeping one edge flat with a ruler.
     
  10. Maxxi
    Joined: Apr 2019
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    Maxxi Junior Member

    "Tortured in parts" is just because real scale plate thickness for the model would have been 0,4mm sheet. Now I only had 2mm sheet so it's superstiff in this scale size. Think of doing a real size build of 20mm sheet.. But then when you build a full size 5,2m long boat of 4mm sheet you realise it's quite flexible and easy to twist. You know you can twist a sheet to a sertain point without deforming it..?

    In this model all sufaces are ruled, where do you see a suface that isn't? Nothing needs to be stretched or compressed, only twisted a little and bended. There is no curvature in two directions. This model can be done of paper or cardboard if you wan't. And what else can you check in Freeship "developable surface"? It just did these sheet rollouts, it wouldn't do them if there is some non ruled shapes.
     
  11. DCockey
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    DCockey Senior Member

    Maxxi - You have demonstrated the flat shapes from Freeship can be assembled into a hull, but what is the shape of the resulting hull? Have you carefully measured your tacked together model and compared it to you design? Take a ruler or similar and hold it against your model transversely. Are the sections of your physical model exactly straight.
     
  12. DCockey
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    DCockey Senior Member

    Any surface which is straight in two different directions and is not flat (a plane) is twisted. As Dejay said all developable surfaces are ruled surfaces but not all ruled surfaces are developable surfaces.

    Most software which is intended to unroll developable surfaces into flat surfaces will also work on surfaces which are not developable but "close enough" in same way.
     
  13. JSL
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    JSL Senior Member

    probably late in the game but attached is a rough example showing the frame (or section line) curvature. Red lines are straight. 86 341 body plan developed pl cropped.jpg
     
  14. Mr Efficiency
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    Mr Efficiency Senior Member

    JSL's drawing shows the convexity forward, that I dare say is also evident in maxxi's model. It would not be a problem except your internal framing won't be contacting the sheeting.
     

  15. JSL
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    JSL Senior Member

    this is how I saw it - no 'convex' - station lines overlay in red. I may be wrong maxxi boat .jpg If right, - probably would not 'plate up'
     
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