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Boat hull loft issues

gary_brattongary_bratton Member Posts: 5
I am new to CAD, but old at boat building.  I suspect some of my spline and lofting on plywood floors may be messing with my digital education.  I have been working on this simple hull form for almost 2 weeks now.  At various times and versions, I have been able to generate the loft, and others I can not.  Why remains a mystery to me.  This version will generate the loft until I add the guides from the hull shear and the bottom of the hull, and it breaks with a very general message.  I have read through the forum, done all the tutorials, and done extensive web searches for ideas, but it still seems to break for random reason and at random times.  I am sure the random comes from my lack of understanding, but if someone experienced could look at this drawing, I sure would appreciate the help.


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    billy2billy2 Member, OS Professional, Mentor, Developers, User Group Leader Posts: 2,041 PRO
    edited April 2020
    Do not use the edges of the boat to define loft. Get the shape right and then trim.

    Don't mess up the hull's shape by using the edges. Separate these actions.


    Focus on the surface shape 1st and get it right. Then come back and trim the edges.

    Trying the build the hull surface using the edges will always fail. Focus on one and then the other.

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    John_P_DesiletsJohn_P_Desilets Onshape Employees, csevp Posts: 241
    edited April 2020
    Hello @gary_bratton

    Thank you for sharing this awesome project with us. You are on the right track creating the proper framework of the boat hull. As @billy2 mentioned, focus on the middle portion of hull first, and finish the ends later.  I copied the project and made some changes to the profiles and guides that drive each surface.  The profiles in your example have a third spline point that is pierced to the guide curve. If you delete that spline point and pierce just the spline to the guide, the curve will be a lot cleaner. 

    Onshape Document 

    Original spline.

    After removing the spline point and piercing the spline to the guide curve. 

    This is the first loft focusing on the mid section. 

    Next, I mirrored the surface to construct the nose of the hull. This could be been done without mirroring the surface but in this example I decided to mirror. Below is the two halves of the boat. I created a 3D spline to form the nose. On the front plane I sketched a spline that will be used as a guide in the next operation.

    Using the fill surface feature, I matched tangency to the edges of the hull and used the sketched spline as a guide. 

    The back of the hull needed some rework. The curves created in  the master sketch have inflection points that will produce a poor surface. I created another 3D spline making sure to match tangency to the edge of the hull surface, and normal to the mirror plane (front). After the 3D spline was created i mirrored it to the other side. 

    This is the lofted surface created at the back of the hull, matching tangency to the edges of the hull surface. 

    This is the end result.  Please let us know how you make out and good luck!

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    gary_brattongary_bratton Member Posts: 5
    Well, I knew that the "real" way to build a boat would be different, but I never imagined this solution.  I will give this a go and see how it works out.  Thanks for the help

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    gary_brattongary_bratton Member Posts: 5
    you guys are awesome.... but I have a lot of unlearning to do.  Thanks you so much

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