http://sparkbluster.com/site/fileallegati/Surfboards%20Idrodinamics.pdf
http://finsciences.com/surfboard-fin-science/
http://eprints.utas.edu.au/6613/1/AFMC_Brandnerand_Walker_2004_F1.pdf
Love it…just can’t help myself…
Thanks for that Wildy.
As its just you and me I can tell you I’m working on a new fin design that doesn’t stall up to 45 degrees. All the theory is interesting and it’s something to initially build a design on but the proofs in the water testing.
Although I’m out of the game lately it’s good to know some serious time is being put in by people like yourself. One of those links shows straight edge fins similar to some I played with years ago.
Love the straight talk from finsciences too…
Watching with interest…
Wildy, How come you’re out of the game ?
I remember you did a lot of 747 style fins like in your avatar.
I never thought the cutaway at the back of standard fins to be overly efficient. Larry Allison does quite a few fins with straight trailing edges too.
Good stuff. Some of the physics in those articles (and others) can also be applied to concepts such as concaves and tail contours.
Not to thread jack, but the Newtonian concept of flow turning, as it applies to aerofoils, has some interesting applications to concaves in the tail of a board.
For example, concaves produce a rail edge that is less than 90 degrees. This throws water down and away from the rail, which is similar to downward flow turning induced from an airplane wing (which creates the predominant lifting force). This I believe is why concaves are often desccribed as producing lift. The board is literally throwing water down and away from it, and since equal and opposite forces must be maintined (One of Newtons laws) the board is ‘‘pushed’’ up and partialy vectored forward.
Ooh, that’s a curly one…
Quote "For example, concaves produce a rail edge that is less than 90 degrees. This throws water down and away from the rail, which is similar to downward flow turning induced from an airplane wing (which creates the predominant lifting force). This I believe is why concaves are often desccribed as producing lift. The board is literally throwing water down and away from it, and since equal and opposite forces must be maintined (One of Newtons laws) the board is ''pushed'' up and partialy vectored forward. "
I wouldnt say that the concave doesn't overly affect the flow because the direction of flow is around 10 degrees off the stringer.
But I would say that concaves reduce lift so that the rails sit lower in the face explaining why concaves need more effort to get going.
A love - hate relationship I’d call it. I love it, but I’ll never ever understand it, at least not the maths. And I wonder what I’m in love with…
A basic question: How come that aerodynamics and hydrodynamics seem to be used interchangeably by many folks? The wing foils used for water fins are derived from aeroplane wing foils, and some claim that certain airoplane wing foils are better for surfing than others, although they operate in water, not in air.
Air is very compressible, but water is not.
So how come they behave so similar when flowing over surfaces? Or don’t they, and we really need to distinguish much more between hydrodynamics and aerodynamics?
Sorry if this is a stupid question, or maybe one that is too hard, but it’s been bugging me for a while.
One of the main reasons for my attenmpts to make snap-in fins is to test them in blinded conditions in the real world waves.
That might answer the question which fins work better than others, and when.
Photo shows a wave grinder fin and two different McCoy Gullwing fins (and my own first attempt at shaping a bird-wing fin) being encased in latex, in an effort to create cheap moulds. That will hopefully make it possible to make a couple of snap-in fins of each variety.
If the fins can be swapped quickly (by a ‘researcher’) and don’t fall out or break off, then a number of surfers can ride their favourite (single fin) board with several different fins it it during a single session, therefore under very similar conditions. And without knowing which fin is in the board (single blind test). With two ‘researchers’, the test could even be designed as ‘double blinded’ (i.e. the surfer does not know which fin is in the board, and the person asking and recording answers about the fin’s performance does not know either).
It’s not a stupid question but you can understand that a lot of people would consider all wings to be the same. And that’s about the end of it. If you don’t know any better, it’s all the same. And somehow identical, like you could surf a 747 or fly a longboard.
For me, a lot of ‘hokey’ theory is about lift, like without it a surfboard will sink. If fins are absolutely and essentially about lift…what about finless craft ?
Wave machines – like Slater’s and the one outside Austin, TX – are where surfboard designs and the related fluid mechanics concepts can be compared, studied and evaluated effectively. For practical purposes, the same wave every time.
Maybe the greatest value of wave machines is the advancement of surfboard design.
That pretty cool all the research and development you’ve put into the gull wing fins, I’m sure you’ve learnt a lot about that fin and fins in general.
Same with Wildy doing all the straight edge fins, he must’ve picked up a lot of knowledge about that specific design.
Stoneburner, certainly wave pools will advance design, hopefully we’ll see some revolution in fin design…
http://www.swaylocks.com/groups/past-present-and-future-fins-proboxlarry
I suspect less is known about rail flow dynamics than fins.
EDIT: Unlike fins, rails function at the interface of two different fluids – liquid and gas.
Reynolds Numbers are the clue you need MrMik if you want to compare “like for like”.
It’s interesting that we all follow the plans of fin size, shape and placement down to the millimetre and consider that we have built something that enhances or at least conforms to the relevant hydrodynamic laws and theories, yet Bill Thrailkill is building a board with no cant and no toe in.
Does Bill exist outside the laws of hydrodynamics ?
Are toe and can’t unnecessary ?
Maybe they’re just the 101 and there’s a lot more room to move ?
Keel fish fins have neither and have worked fine for decades… Angle of attack does not need to be preset. My question is, why are surfboard fins still fixed in place and for the most part ridgid in shape? Airfoils are neither and haven’t been since Curtis and the Wright Brothers fought over patent rights…still in the dark ages here. Fins should warp and be controlled by wire…no?
Keith, I suppose everything is how it is due to business forces. But I’m sure they all have a selection of great concepts in hand.
“Fins should warp” you say and I’m working on something you should enjoy. They warp in performance not physically.
Surffoils wrote:
They warp in performance not physically.
You were looking for a name. They are your Warp Drive Series – Warp 1.0 through Warp 9.0.
Beyond that, Trans-Warp Conduits.
Bill W, you know too much already !! Haha
But thats a great name, thanks - Warp Drive Fins.
‘‘Does Bill exist outside the laws…?’’ The short answer is yes. (That would be the laws as others misunderstand them.) My understanding, and application, is just different.
‘‘Are toe and cant unnecessary?’’ The short, and the definitive answer, is also yes. People forget that I’ve been toying with multi fin setups, since 1964. I simply learned a few things, along the way. I was doing ‘‘cant studies’’, with removable tri-fins, in 1971.
Surffoils, too bad you live so far away. We could have some real fun, working closley together, on some of this stuff. If only, eh?