Fins desing and information

Hi everybody,

 

Awesome forum. I’ve been reading it since 3 or 4 years now, and finally decided to login.

 

I’m searching information abour surfboard fins. The reason is that i’m going to finish my studies this year (Engineer), and I need to make a research about something using the tools that I’ve learned. I decided to focus my report in removable fins, specially in different systems stiffness.

 

I would like to read what is written about fins before starting my own research.

 

Has anyone knows where i can star searching?

 

Thanks to all people.

A couple years ago I worked with Dr. Dave Carswell on his doctorial thesis regarding fin design. It's not materials heavy. It was used to develope a software program for design. But, if you send me your e-mail address I will send you a pdf file of his thesis. I also manufacture injection molded fins boxes and other surf related components. So, I might be able to help you out with some specific question in that area.

 

tom@daumtooling.com

Sounds like a neat project.

But I'm curious about your comment - “I decided to focus my report in removable fins, specially in different systems stiffness.” Are you interested in the material science aspect, or the structural design aspect? I realize the two areas overlap, so perhaps my question is which will have the greater emphasis?

By the way, I would guess that you have done some investigating into the mechanical loading of fins for different fin geometries? Or even better, fin dynamics (in general) for different fin geometries? If so, sharing that kind of data would be greatly appreciated, well, I sure would enjoy reading about it.

kc

 

ps. By the way, who are you? Your profile says little. And what is your area of engineering specialization? What program? ... and one more thing... you don't have to answer any of my questions... really, only if your so inclined...

Hi kcasey,

 

I just created my profile yesterday, so I hadn't have enough time to write about me. Now there's a bit more information about me in my profile.

 

Answering your question about if I want to focus my report on materials or structural design, it's difficult to me to tell you right now, but I would like to studie structural design about removable fin systems just cause I'm mechanical engineer. My goal is to obtain a fin plug design stiffer than actual plugs, because i've always heard (and I think too) that stiffer plug are better. In my opinion a stiffer plug gives you the chance to work only with fin stiffness.

 

Anyway, this is just a goal. Don't know if it would be possible to develop or not, in any case this would be the second part of de preoject.

 

The first part of the project it's going to be a research about actual fin systems. To do this research I'm going to follow some steps:

1.Obtain fins geometry. It's a bit difficult cause manufacturers, obviously don't want to share their designs, so I'm going to use what we call "invese engineering". Using some machines and informatical tools, make an approximation of some fins geometry.

2.Using CAD programs (in this case CATIA) create a model of fins and plugs. Probably in this step bottom concaves, vees and other forms would be rejected. I don't like this idea but it would be extremelly complex to work with concaves, and I want to studie fins performance, not fins+surfboard performance.

3.Using the model created on step 2, make simullations using FEM and evaluate what happens on fins trying to understand their performance. Make simullations with different materials and try to understand how flex influences.

 

In that point I'll evaluate if I can follow the researsch or not. (I would like to finish this project in June 2010).

 

Obviously I'm still searching information and this idea could still change, but it would be great to make that research.

 

Thank you again, and sorry if my english is hurting, hehehe

My English is hurting too... and sadly, it's my first and only language.

Sailboat keels are not surfboard fins, but they have a lot in common. I mention this because the terminology for fin geometry and its respective mechanical/dynamical impact for sailboat keels is far more sophisticated and precise. The main reason for this is fairly obvious – historically, there has been a lot more money to be made in understanding and perfecting sailboat keels.

But it's not just the terminology, it's also existence of simulation software  in the keel design sector, which, dedicated or adapted, might allow one to sort out the impact of different geometries -e.g. the impact of surfboard fin rake, which in keel terminology is captured by sweep angle, on the lift/drag ratio, and possibly the force distribution profile in general, which may be closer to what you're after. I wouldn't know for sure, but since you're an academic, they may be more forthcoming and allow you to use it, if not run a few test cases for you, possibly even allow you to rewrite a bit of it, adapting it to surfboard fins.

There is also the mesh software used by Carswell, see tomatdataum's post above. (Of which I know squat about.)

I do suspect however, that making the standard static assumptions and modeling the force to be concentrated at the centroid  of the fin's plan-form is sort of lame. For one thing fins are generally foiled. The simple centroid treatment provides a limited to marginal degree of insight as to whether a given fin with a given geometry and installation will fail. If my understanding of where you might be taking your research is correct, it would be nice to have a better understanding of the structural role of foil and how it impacts the stress distribution -i.e. the role of foil as a purely structural element, even if it's only a by-product of it [your research].

I do have an interest in fin function and structure, but it's amateurish at best, so whether or not any of the my above comments will be of value is questionable. Also, I'm still not completely clear as to where you're placing the emphasis in your project... and quite frankly there's no need to for me to be all that clear... it's your project... and anyway, 'emphasis' does have a way changing.

Swaylocks has any number of fin experts (on function, geometry, systems, installations, and production) who occasionally post. They range from owners of companies, to sales reps, right down to your local fin aficionado, cranking off the occasional 'next big thing in fins'. Sort of like johnmellor's latest  tunnel fin  – which has inspired Schick's new product line for lady Right Whales looking for that hairless (barnacle free?) under-fin look. Anyway, they're all easy enough to find, just do a search on fins and they'll pop up.

Thanks, I hope you keep the forum informed – even if it's just the occasional interesting bit of insight.

kc

Kcasey,

Sail boat appendages do have a lot in common with surfboard fins when you are looking at directional control, lift/drag ratios and attachment techniques. Where the two diverge is when you study how to kinetically propell yourself via pumping.

Prior to managing a custom injection molding facility I used to manage a boat yard that specialized in optimizing racing sailboats. I still race sailboats. As a matter of fact, we just won our class in Transpac last July on a Santa Cruz 50 "Horizon". And, in September I was up in San Francisco racing a new Antrim 40 at Big Boat Series. So, I have very close ties with many of the top sailboat designers. I mention this because much of my design development has been influenced by the hydrodynamics of sailboat appendages.

One area that I believe Future fins has a design advantage is designing fins which work better in kinetic propulsion. When you need to pump to gain speed, their fins do work very well. It's just that the design characteristics that help a surfer to grovel also limit the efficiency of their foils at speed. So, the fin foils that I've developed work great at controlling power and the foils Future has deveolped (in my opinion) work well when you need to generate power.

I’m a bit confused about what it is you want to figure out? You say fin plug stiffness? Aren’t they all stiff? They are not meant to flex, are they?

Then you say you want to study a fin’s performance? The fin’s performance, or the effect of the fin system on (identical) fins’ performance?

I think an interesting topic would be how fin plug systems affect overall BOARD stiffness/flex. FCS made a big advertising campaign about how their little plugs didn’t stiffen up a board like other systems…then they come out with FUSION plugs which basically mimic the other systems.

Finally just to throw out another hot topic- especially with multi fin boards, a big issue in my opinion is the overall weight of fins + systems + install. I have a five fin board which I believe is slightlly handicapped by the tail weight, forcing me to ride further forward than the design would dictate.

Maybe I wasn’t clear enough.

The terminology used in the keel sector is currently well developed, more sophisiticated and precise and lends itself to a more scientific/engineering treatment. I completely agree that sailboat keels and surfboards depart functionally is some pretty important areas (that’s a real understatement.) But some of the science/engineering tools are seemingly already available, as in the simulation software, which itself was likely adapted from aeronautics.

In the end it will likely have to move to the ‘test tank’, but surely it’s reasonable to draw upon existing body of terminology, as it relates to quantifiable observables. This does not mean that qualitative  descriptions or testimony are of little or no value, on the contrary, they’re likely to drive a greater sophistication of the former [quantitative observables]. 

In fact, I suspect with the kind of breath and depth of ingenuity generally associated with engineers, it’s probably pretty reasonable that modeling (possibly simulating?) , say Kinetic Pumping for example, is a real possibility. (By the way, it sounds like you may have already done as much? If so that really would make for some interesting reading, in particular the parameters of the model… if it’s not proprietary of course.)

Basically, my reference was to the possible utility of an existing body of terminology which is more precise, especially with respect to geometry, which could easily be developed/adapted further. I’m not inclined to see it as a polarizing issue, why would it be?

Also, and I realize this might turn out to be a sensitive topic, though the current market thrust (and justifiably so) is centered around shortboard fins systems and installations
, there are other kinds of fins etc. out there, and there respective geometries are all over the place. I don’t know where bidi will be putting his emphasis in this respect, but wherever it is a more common precise terminology couldn’t be anything but helpful.

kc

 

kcasey,

If you haven't read Dave's thesis, I'll be perfectly happy to send you a copy as well.

There is a body of terminology available from naval architecture which is a subcategory of hydrodynamics which is in the same arena as aerodynamics within mechanical engineering. I'm confident that Josu will adhere to the terminology of his chosen discipline. But, he has already stated that English is not his first language.

lilibel03,

Not all attachment methods are created equally. Different materials and different geometries have a great affect upon how tortional loads are distributed.

Tomatdaum. I stand corrected. I’m more curious about the Antrim 40. It’s the ones with the chines? What’s the thinking behind that? Reminds me of Ragtime. You can PM me as I know this is way OT.

You’ve already provided me with a copy, and I’ve read it. Yet I’m still under the impression that a more precise terminology (as opposed to that commonly used in the surfing culture) regarding fin geometry would be a good thing… go figure. But that really wasn’t the (major) point of Carswell’s thesis - which was a nice piece of work. 

As for origins of the terminology, I think I suggested as much in my post. But it would appear that there are existing software packages (perhaps including Carswell’s mesh treatment, published or unpublished) that because they are being used by an industry which is concerned with a product that has similar geometry, operates in a similar environment, likely uses similar protocols in testing, and ultimately has some overlap in terms of function, it seemed to be to reasonable to merely mention its existance.

You see, I do not know bidi, nor exactly what he’s up to, nor where he’s been or coming from with respect to all this. Which of course is no fault or burden of bidi’s - which is hopefully clear to bidi. But whatever it turns out to be, I hope it works out well, he gets the answers he’s looking for and he has some fun doing it.

kc

kc,

     Totally agree...most everyone who post here is trying to advance the state of the art. And, using consistant & common building blocks is vital to that advancement.

 

      I noticed you mentioned tank testing to analyze characteristics. Dave actually used tank testing on our range of fins in order to validate a baseline to develop a lift drag prediction program. He did touch upon flex as a potential variable. But, the flow rate of his tank was not sufficient to develop a data base with flex included.

 

      Oh well, I'm an advocate of stiff fins and secure attachment methods which end up minimizing that variable.

I’m an advocate of stiff fins and secure attachment methods which end up minimizing that variable.

Amen!  Oh, wait, I learned that from you… Ha! 

Plus the structural integrity  around the whole thing - board, box, fin.  I like it stronger than not, and, being me, I don’t notice big differences in weight - as has been pointed out, some worry about an ounce or so, then put on a quarter pound stomp pad…

i have a couple of papers but they are too big to attach

here’s the info on them you can research the rest and download them online from the source.

The Swansea project seems to be the closest at doing what you are thinking about.

PAPER PREPARED FOR THE 4TH INTERNATIONAL SURFING REEF SYMPOSIUM, NATURAL
AND ARTIFICIAL SURFING REEFS, SURF SCIENCE AND COASTAL MANAGEMENT,
JANUARY 12-14, 2005, MANHATTAN BEACH, CALIFORNIA

Optimization of Surfboard Fin Design for Minimum Drag by Computational Fluid
Dynamics (Do glass-on fins induce less or more drag than boxed fins?)

Nick Lavery1, Graham Foster b, Dave Carswell, Steve Brown
Materials Center of Excellence for Technology and Industrial Collaboration

University of Wales Swansea,
Singleton Park, Swansea SA2 8PP, Wales

b Jones & Foster Design Ltd, Swansea, Wales
United Kingdom

Abstract
This paper describes work being done at Swansea University on the design of wave riding
surfboards, with preliminary emphasis on the stabilising fins. Two specific CAD (Computer
Aided Design) tools are being developed, one for surfboard design and the other for fin design,
both of which allow export of NURB (Non-Uniform, Rational, B-spline) surface geometry in the
IGES (Initial Graphics Exchange Specification) format. The fin design tool has the capability of
allowing different National Advisory Committee for Aeronautics (NACA) foils series to be set at
separate cross-sections along the fin.
Fins and surfboard/fin combinations can be imported directly into the CFD (Computational Fluid
Dynamics) package FLUENT and with careful consideration of surfing dynamics to obtain values
of critical flow variables, estimates have been obtained of the pressure and friction drag forces,
which are thought to correspond to those occurring in practice and will be validated
experimentally at a later stage. These results, however, have already been used to examine a
number of disputes in the manufacturing industry, one of which is whether glass-on fins induce
more or less drag than equivalent fins fixed to the board by a box.
This component of the research is just a small part of the larger objective which is to bring
scientific and engineering advances into the design and manufacture of surfboards. As the project
progresses, CFD will be used to resolve more complex drag components, such as wave drag (free
surfaces), induced (vortex) drag and cavitational drag, as well as being coupled to a finite element
stress analysis to optimize flexural properties of boards and fins

 

Research Paper Two:

HYDRODYNAMICS OF SURFBOARDS
FINAL YEAR THESIS BY MICHAEL PAINE
BACHELOR OF ENGINEERING (MECHANICAL)
UNIVERSITY OF SYDNEY
1974
Michael Paine 21 May 2001.