Wednesday, March 2, 2016

Ellipse-Based Surfboard Fin


I started working on the ellipse-based fin concept in April and May of 2015 as posts in a thread at swaylocks.com.






A NACA 0009 foil profile was used.


FinFoil CAD diagrams and the first CNC shaped protoype of my elliptic fin design below are courtesy of JRandy at swaylocks.com.









Computational Fluid Dynamics figures below for the fin design were created by Hans at swaylocks.com.
http://www.swaylocks.com/comment/512804#comment-512804





Links to the other elliptic surfboard design posts:

Ellipse-based rails
http://ellipticsurfboard.blogspot.com/2015/11/ellipse-based-rail-profile.html
Ellipse-based rocker
http://ellipticsurfboard.blogspot.com/2015/11/ellipse-based-surfboard-rocker_13.html
Ellipse-based planshape
http://ellipticsurfboard.blogspot.com/2015/11/ellipse-based-surfboard-planshape.html
Ellipse-based tail template
http://ellipticsurfboard.blogspot.com/2015/11/ellipse-based-tail-templates.html

Friday, November 13, 2015

Ellipse-Based Surfboard Rocker



The following examples are used to explain a method for creating ellipse based surfboard rockers.  These rocker examples are for illustration of the method.  Actual ellipse heights and lengths must be adjusted to create rockers that are suitable for specific surfboard designs.

The blue ellipse-based rocker shown above was done with 2 ellipses of different sizes joined at the (vertical) midline when completed.  Both Ellipses have the same width (same as board planshape).  Pick the desired nose and tail rocker heights.  Draw a straight line the length of the board -- I used a rectangle instead of a straight line.   Mark where the surfboard wide point would be on that straight line.  Align the (vertical) midline of each ellipse with the widepoint mark on the straight line.  Now place marks (or boxes) of the desired nose and tail rocker heights at the appropriate ends of the straight line.  Stretch the length of each ellipse, independently of one another, until each elliptical curve touches the corner of both the nose and tail boxes.  Join each of the half-ellipses at their midlines.  Trim the ends of the ends of the ellipses off at the points where their curves are touching the box corners at each end of the straight line.  This creates an ellipse-based surfboard bottom rocker.


Hope this makes sense.  Turned out wordier than expected.  Very simple when viewed and created as a graphic (below).  Purple is the nose rocker ellipse and red is the tail rocker ellipse.  Green boxes are 2.0" high (tail rocker) and 4.7" high (nose rocker).  Board length is 7'6".  Line widths were increased from 1.0 pt to 1.5 pt for blog posting.


Combining Ellipses with Different Heights

Thanks to Ryan for bringing up ellipse height and rocker shape in his comment below.  I chose ellipses equal to board width in the example above for the purpose of discussion.  Varying ellipse height changes the shape of either nose or tail rocker curve.  Increasing ellipse height will make the curves rounder.  Decreasing ellipse height will make the curves flatter.  That is, as ellipse height gets closer to its length, the curves become more circular.  As ellipse height approaches zero, the curves become flatter.  While the ellipse curve becomes flatter overall, with decreasing height, the curves near the tips become steeper.  Also, with ellipse height fixed, the curve becomes more circular as the length shortens and flatter as length increases.

The figures below all have the same tail ellipse (height = board width).  Board length is still 7'6" (blue rectangle).  Two of the nose ellipse heights are greater (top figure) or less (bottom figure) than board width.  Ellipse lengths must be stretched or compressed accordingly.  (Ellipse heights cannot be less than 2x nose or tail rocker height.)  



Links to the other elliptic surfboard design posts:

Ellipse-based rails
http://ellipticsurfboard.blogspot.com/2015/11/ellipse-based-rail-profile.html
Ellipse-based planshape
http://ellipticsurfboard.blogspot.com/2015/11/ellipse-based-surfboard-planshape.html
Ellipse-Based Fin
http://ellipticsurfboard.blogspot.com/2016/03/ellipse-based-surfboard-fin.html
Ellipse-based tail template
http://ellipticsurfboard.blogspot.com/2015/11/ellipse-based-tail-templates.html








Ellipse-Based Surfboard Planshape

I have been working on elliptic surfboard design techniques for several years.  I came up with an ellipse-based planshape/template method that satisfied me this year.
                                                                                                                                                    







My ellipse-based panshape started 2 or 3 years ago as a retro fish template that I stretched to make a new template.  After a bit, I decided I could use a half-ellipse placed at the surfboard's widepoint for the nose, to get more streamlined curves for the front half of the shape.  I was going to combine it with the stretched tail section of a retro fish.  After a while longer, I decided I could stretch an ellipse to create the tail section for the planshape.  I averaged the widepoint positions, relative to length, from retro fish designs to place the position of my widepoint.  I joined the half-ellipses at the location of the surfboard widepoint (purple line).  I decided that tail end width (blue line) should be 61.8% of the surfboard's wide point (Golden Ratio).  What started as a Stretched Retro Fish became an entirely new ellipse-based planshape.


I have never posted my design or method for this all ellipse planshape before today.  I posted the "concept" once in a Sways "computer/CAD hate thread" to prove you could use simple computer programs to create and compare designs from an existing template -- and create entirely original surfboard designs.

Semi-elliptical planshape.  I created it with a stretched retro fish tail and a half-ellipse nose joined at the surfboard's widepoint.  I posted it in a Swaylocks thread (page 4, post #41):



From Retro Fish to new shape with new dims?
Done quickly with PowerPoint, Photoshop and a computer --"Computer-Aided Design?"
I find the computer useful for exploring design possiblities ...




Ellipse-Based Surfboard Rail Profile


13 November 2015

The method and figures described below were inspired by the original rail profile design method found at this link:
  
This solid green shape was my first attempt at an ellipse-based rail profile.  I was not satisfied...


21 November 2015

Ellipse-Based Rail Profile (Refined)





Board Thicknes = 3 inches for this example
* Red rectangle = 3" x 6"
* Large Ellipse (green): Height = 2 x 0.618 x red rectangle height; Length = 2 x ellipse height
* Small Ellipse (purple): Height = 2 x 0.382 x red rectangle height; Length = 2 x ellipse height
* Align ellipse (horizontal) midlines at 0.382 x red rectangle height (top of blue rectangle).  Ellipses are tangential to the left wall of the red rectangle.

Vary ellipse lengths and/or alignment of the ellipse (horizontal) mid-lines at new percentages of rectangle heights, to create different rail profile shapes.  Ellipse heights must be adjusted to conform with each new percentage of rectangle height. 








Links to the other elliptic surfboard design posts:

Ellipse-based rocker
http://ellipticsurfboard.blogspot.com/2015/11/ellipse-based-surfboard-rocker_13.html
Ellipse-based planshape
http://ellipticsurfboard.blogspot.com/2015/11/ellipse-based-surfboard-planshape.html

Elipse-based fin
http://ellipticsurfboard.blogspot.com/2016/03/ellipse-based-surfboard-fin.html
Ellipse-based tail template
http://ellipticsurfboard.blogspot.com/2015/11/ellipse-based-tail-templates.html





Ellipse-Based Tail Templates

I have been working on ellipse-based surfboard design techniques for several years.  This year I came up with an ellipse-based method for re-designing the earlier/first versions of this tail shape.

For information about the origins of this tail template concept, click these links:
http://bgboard.blogspot.com/2013/08/angular-dolphin-tail-or-wingtail.html
http://bgboard.blogspot.com/2015/03/dolphinwing-tail-evolution-aka.html




Links to the other elliptic surfboard design posts:

Ellipse-based rails
http://ellipticsurfboard.blogspot.com/2015/11/ellipse-based-rail-profile.html
Ellipse-based rocker
http://ellipticsurfboard.blogspot.com/2015/11/ellipse-based-surfboard-rocker_13.html
Ellipse-based fin

http://ellipticsurfboard.blogspot.com/2016/03/ellipse-based-surfboard-fin.html
Ellipse-based planshape
http://ellipticsurfboard.blogspot.com/2015/11/ellipse-based-surfboard-planshape.html