Help with Strake Modeling

Discussion in 'Boat Design' started by Matt Culik, Aug 22, 2022.

  1. Matt Culik
    Joined: Aug 2022
    Posts: 2
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    Location: NJ

    Matt Culik New Member

    Hi. Total newbie here.

    I'm trying to 3D model my take on a Bertram 31 hull in Fusion 360 based on drawings and photos I've found online. I've got the basic hull form figured out (I think...), but I'm having difficulty with the strakes underneath.

    Here are some pics of the strakes:

    Cardinal Trailer Specs for Bertram 31 Hull https://www.bertram31.com/specs/index.html
    https://www.thehulltruth.com/4749012-post205.html

    I have tried tracing the strakes in 2D in Fusion 360 and then extrapolating to 3D, but no matter which way I do it (start with a top down view, start with a profile view, etc., etc.), they get all messed up. I even tried calculating the XYZ points using interpretations of best fit lines and some trig, but I can't get them to work either.

    Basically, I'm hoping this forum can help me understand how strakes move on the bottom of the hull, and what is the proper 2D way to think about strakes when drawing a boat.

    For example, are the strakes always parallel to the centerline and just give the appearance of moving up and in because of the curvature of the hull? And should I think of them as part of the station drawings, or is it easier to think about them when looking at the hull from top down?

    Also, I just want to confirm another thing that my eyes might be messing with, which is that the deadrise of the Bertram 31 increases as you progress to the bow. Is that correct? I have it at the quoted 24 degree deadrise from the stern to about amidships, then tapering inward from there to a final deadrise of 50 degrees at the bow. Does that sound right?

    Thanks!
     
  2. bajansailor
    Joined: Oct 2007
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    Location: Barbados

    bajansailor Marine Surveyor

    Welcome to the Forum Matt.

    Is it possible to post any copies of your Fusion drawings on here?
    I am no expert, but there are expert CAD folk on here who should be able to help, if they have something to start with, for reference.

    Re the hull deadrise, yes, it will increase as you go forward from amidships to the bow.

    Re the strakes, I think you mean the chines (?) - maybe you could think of them as being similar (in a way) to the diagonals on a lines plan, at least in the bow section? Aft of midships they all appear to be parallel to the hull centreline pretty much.
     
  3. Tops
    Joined: Aug 2021
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    Location: Minnesota

    Tops Senior Member

    Aloha and Ahoy Matt,
    How are you modeling the hull, lofted stations?
    Picture from the second link.
    b31.png

    I tried a sweep of a triangle, using the upper 'chine' as a path and the hull as the guide surface.
    b31_2.png
    Something like this might work once you can figure out the path (if you have the profile and guide surface).
    b31_3.png
     
    Last edited: Aug 23, 2022
  4. Matt Culik
    Joined: Aug 2022
    Posts: 2
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    Location: NJ

    Matt Culik New Member

    @Tops - GREAT tip on the sweep + guide surface. Thanks! I was trying to add the chines with sweep, but was having a problem getting the path I wanted. Last night, I turned a profile view of the chine spline into a surface and split my hull body using that, then swept the chine profile along the resulting edge of the hull. It's the closest I've gotten, but I think your approach might be faster and achieve the same or better results. I'll mess around to see if I can get it to work.

    I'm modeling using lofted stations. I started by creating 10 stations based on dimensions taken from the drawings I could find, plus some spline tracing of pictures. That worked OK, but the resulting hull wasn't correctly smooth from bow to stern. So, I plotted the rough points in Excel and then generated best fit equations for all the lines so that I could calculate points at stations spaced 12" apart. I also did a bunch of trig calcs to try to determine the splines at each station, but that didn't work as well as I'd hoped it would. Long story short, I ended up with all the basic points to comprise each station spaced 12" apart. From there, I graphed the various lines and "numerically faired" them. At this point, I just need to do some cleanup for lines that end in between stations, and then I'll be able to post a picture.
     

  5. fallguy
    Joined: Dec 2016
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    Location: usa

    fallguy Senior Member

    Given the flow under the keel, any competing flows would impart drag. So, everything must be even with the keel.
     
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