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J
JS_137630744-Participant
4-Participant
July 8, 2025
Question

Surfboard fin modelling

  • July 8, 2025
  • 4 replies
  • 1506 views

Hi, I am currently trying to model a surfboard fin using a fin outline I found online and with an MH32 airfoil profile. I used points to make a datum curve for references to the boundary blend I made.

I want to check that this geometry is okay or not as visually I can see at the top of the fin there looks like a misconnection between either blend surfaces, but I can't tell if it is just visual.

 

I used mesh surface to see it looked weirdly shaped at the top and using the reflection you can see it reflect on the top too.

 

Is there any way to fix this if this is the case, or is there a different way to do it with an asymmetric foil shape?

Thank you,

Joel

JS_13763074_0-1751977543712.png

 

4 replies

P
19-Tanzanite
pausob19-Tanzanite
19-Tanzanite
July 9, 2025

Could be your display settings.

Try going File->Options->Model Display->set shade quality to 11 (or beyond 🙂

 

pausob_0-1752081481704.png

 

J
JS_137630744-ParticipantAuthor
4-Participant
July 10, 2025

Thank you for the suggestion! It didn't work unfortunately, just made the misalignment more apparent haha. This is what the tip of the fin looks like currently, as if it has split it by the junction of the two foil sketches:

JS_13763074_0-1752128658679.png

This is what I mean by the two sketches:

JS_13763074_1-1752128748130.png

 

 

tbraxton
22-Sapphire II
tbraxton22-Sapphire II
22-Sapphire II
July 10, 2025

Assuming there is a plane of symmetry (mirror plane) on the long axis of the fin. Build half of the fin and set the surface boundaries on the mirror plane to the required angle relative to the mirror plane. If there is not a dihedral angle at the mirror plane, then set the boundaries of the surfaces on the mirror plane to be normal to the plane.  Once you have half of the fin built in this manner, mirror the quilt(s) and merge them together, you can then solidify a closed quilt.

 

Based on your picture of curves posted above, you probably need more internal curves to get the control you need for this geometry. In general, you want to build all quilts as 4-sided constructs where possible.

 

tbraxton_0-1752145778170.png

 

Patriot_1776
Patriot_177622-Sapphire II
22-Sapphire II
August 5, 2025

Something like this?2025-08-05_SURFBOARD_FIN-01_V1.jpg2025-08-05_SURFBOARD_FIN-01_V2.jpg

    Patriot_1776
    Patriot_177622-Sapphire II
    22-Sapphire II
    August 5, 2025

    https://www.youtube.com/watch?v=7IEYDJ7CqCI&list=RD7IEYDJ7CqCI&start_radio=1

    Patriot_1776
    Patriot_177622-Sapphire II
    22-Sapphire II
    August 13, 2025

    ...aaaannnnd he's gone.

     

    Ah well, I had fun.

    B
    ByDesign12-Amethyst
    12-Amethyst
    August 19, 2025

    I have done a lot off airfoils for wings which are similar to what you show. If shape really matters to you, then you have to control it all the way along, not just at the root or even a few places like @tbraxton suggests. Creo will mutate your airfoil shape to all sorts of weirdness - kind of like an airfoil, but not the definition you wanted - except at the root.

     

    Of course you can just make a pretty model with nice surfaces if that suits your need, but if you really need / want the airfoil geometry, then you have to accurately define it all along. Creo does not do that well unless you build the part in ways the underlying geometry wants to follow it. A blend will probably never get you there.

     

    I suggest a Variable Section Sweep. A quick overview (from Pro/E) is at https://www.synthx.com/tom/sy_tip_9811.htm  That uses 3 control curves, but you will only need 2 (plus the direction trajectory).

     

    Build it from the root to the last parallel "true" foil plane. Use the leading edge and trailing edge curves as the driving curves. Build the airfoil section (with appropriate relation equations - trajpar) so it scales with the distance between the leading and trailing edges. (I find minimally defined splines do that well.) Make sure the trajectory you are following is perpendicular to the direction of fluid flow, and that nothing in the section connects to it. Your variable section must be scalably correct the entire length.

     

    As a practical matter, it appears that the curve you show goes to sharp, which - if this will be a real part, won't work.

     

    Once the Variable Section Sweep is created, you can work on the tip using curves and surfaces. From a practical standpoint the airfoil shape at the tip is sort of meaningless (as long as it smoothly caps the wing shape), so blend it as needed with surface geometry. @tbraxton is right about 3 sided areas, but use long thin 4-sided shapes that wrap around following the curve from leading edge to trailing edge, then the final surface will be a football shape with 2 sides.

     

    Good luck.
    __________

    Alternatively, use equation driven sections then surfaces. (You will have to come up with the equations to describe the airfoil.)

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