check out the date of this study…
http://www.stormingmedia.us/15/1547/A154773.html
An Experimental Investigation of the Scale Relations for the Impinging Water Spray Generated by a Planing Surface
Terry Hendricks ballparked the turbulent layer at 3/4" (18 mm) in his 1969 articles.
more interesting hits
http://www.stormingmedia.us/10/1050/A105083.html
Quote:
the turbulent boundry layer of water that runs along the bottom of your board is actually the same water that realeases from your rail edge when on the rail…
thus that gives an indication of how deep the boundry layer actually is,
I’ll buy that… so the next popular thread goes like this… “how thick is your spray?” Size does matter! 
Bert
Yes what you say makes sence
However I ve just come from having a surf today in small 3-4’ faces and the board is very nice to ride loose but still drivey and with out doubt quicker
So I have done nothing to change the bottom laminar or turbulent zones
But have I now stopped the flow under the board and accross the fins from mixing therefore making the fins produce much less drag
I think with a simple drag test behind a boat with scales to measure the pull force we can find out
A long time ago in yacht design we found that fillets both on the sides and fore and aft edges of foils were slow so nothing really new there
Where I think we should look to now is keep the cutaway fore and aft parts of the fins and now try differend plan shapes ie different rakes,tapers and leading edges
We may find that more conventional airodynamic planshapes will work much better when they are more isolated from the boards existing laminar and turbulet layers
I look forward to seeing where we all can go from here
Regards Mike
Okay I guess should explain my simple drag test
Its simple ie no turning or human rider this just adds too many variables
Take a board that rides well with the cutaway fin setup
Now attach a static weight around the seventy to eighty kgs incorporated with this a fixed tow point
Tow this a couple of times and adjust the weight fore and aft to get a trim similar to a board being ridden in a straight line I would suggest a speed of around eighteen to twenty knots
Once this is set up attach the tow line (ideally a length of 2 to 3mm spectra cord ie no weight and very little stretch) to the boat via a acurate scale ie fish type etc
Now first tow the board at a set speed with a set of standard type fins
then repeat with cutaways (it would be best if the cutaways have the same profile and camber)
If the theorys are correct you should see a slight difference
It should be only slight as in this straight line tow the fins are not producing lift which would change the drag amount
If this shows a reduction in drag it would be only due to the fins not inheriting some of the boundry layer turbulence
If this proves correct then we can start working on lower drag fin profiles and cambers
Regards Mike
PS If this does not show any thing them maybe its the placebo effect
in which case who cares as long as it makes you feel like you are surfing better!
sabs, I started with a basic trapezoid fin. Front edge rake 35 degrees, 1.5 inch wide tip, 5 inch wide base, 7.5 inch deep.
Then, lop an angled inch off the front and rear at the base, for the cutaway.
Then, do a series, 5 degree steps in rake angle, with the base chord length and cutaways the same.
Then, do a series, half inch base width changes, with the tip width and rake angle fixed.
I ended up with a steeper angle than I would have guessed, and a slightly longer root chord with than I would have thought.
Changes in rake angle change how quickly the drive sets in when you angle the fin. Steeper sets on faster. A 5 degree change is easily noted. If it is too steep you can stall it on harder turns.
Changes in root chord length scale the whole thing up, but also drag a little more. A half inch is easily noted.
Throughout all, the basic fin stays a trapezoid. Very easy to make parametric adjustments. The first tests I did were the cutaways. They’re actually a small player compared to a 5 degree change in rake or a half inch change in root chord.
Hi Blakestah
Here are some pics, the first is the cutaways I have just started playing with
As you can see the plan shape is the same old boring fin thats been around for a long time.they are cambered one side and flat on the other
The others are my sloted quad setup,these are the trusted ones ive had for years
The other fin is the small rear fin I some times use with the quad setup
These are still the quickest and the setup that is most drivy and loose
I have tried variations on these with the rake more upright
Maybe with the incorporation of the cutaway I can achieve this
After many years of designing and flying hanggliders,flying sailplanes and yacht design and sailmaking where in most cases a higher aspect and less rake improves performance I would still like to get rid of some of the rake in surfboard fins
The other area where I see problems with the “modern” fin is in the position of max camber
In a hangglider ,windsurfer and yacht the camber is allways well forward,this is to make a foil that is pitch stable
The reasons for this in hangliding are so you dont have a pitch instability as they have no rear stabilizer
In a yacht it helps reduce weather helm that creats drag from the rudder
In a windsurfer it makes the managable
In a sailplane however the max camber is further aft giving better lift for speed and deploying flaps increases this even more allthough increasing drag (there is no such thing as a free lunch)
However a sail plane does not need a pitch stable foil as it has a stabilizer aft to do that job
If you look at the stabilizer you find that the camber is well forward as this foil needs to have pitch stablity
The point of all this I think is that a surfboard fin has no need to be pitch stable all it has to do is provide lift and lots of it when required
Much like a airoplane propeller
But with minimal drag theres the lunch bit
Then when not providing lift it needs to be low drag
So as I see it the quest is to creat a high lift low drag foil
The cutaway is a good start,now I think we need to focus at the next big drag area the tip vortice
For this we need to look at the plan shape and the rake
What do you think
Regards Mike
more pics
ps those links were great guys
When I went through this a few weeks ago, I thought the purpose of rake was stabilizing at higher angles of attack. Sailboard fins have the least rake, longboards have a little more, and surfboards even more.
Rake is surprisingly conserved throughout surfboard fins. I went and downloaded the images from Red-X and other fin manufacturers, and almost all had leading edge rake of 35 degrees at the base - despite them coming from a wide number of designers.
Longboard fins have a base leading edge closer to 30 degrees, and some of the pivot fins are 25.
This is consistent with the AOA argument. Shortboards can have larger AOAs than longboards which turn harder than sailboards.
Rake also changes the onset of lift. Steeper rake has a larger onset of lift. I thought for my rotating system I’d be able to use a steeper rake than normal, because the fin turns to reduce the AOA. It worked out well, but of course the devil is in the details.
On another topic, we’ve been discussing the thickness of the turbulent layer. But below that, there is still laminar flow - water being dragged in the same direction as the surfboard. As a result, the deeper water moves faster relative to the fin than the shallower water. So, another goal, is getting more fin area deeper, where it is more efficient. This is probably more relevant to the larger cutaways in the Mental template design than avoidance of the turbulent layer.
Of course, putting a lot of area closer to the tip gives eddy problems.
sabs im liking what im hearing already,your gonna fit right in here…
one of the biggest reasons i dont run any current fin system is ,all of them have to low a camber and it sits to far back for the low speeds that surfboards operate at ,plus surfboards are doing way sharper angles of attack across a broader range of speeds , so even tho you lose part of your free lunch to drag , the trade off is way more hold and control when running higher camber further forward , but the extra drag is only apparent in straightline speed, as soon as theres the slightest angle of attack ,higher camber further foward foils end up having less drag…
your biplane looking fin must work real well ,coz no matter how high the angle of attack your always gonna keep water attached to the low pressure side of the inside fin, its one of those 6 of 1 half a dozen of the other scenarios,
i can see the logic in that design , its a way of making lower camber fins more efficient,at one stage i was thinking in that direction,
here are some of the down sides to that one .at any given speed you will have more viscous drag because of doubling the surface area …
also the space between the fins ends being a low pressure area ,so the outside fin doesnt have as bigger pressure difference between the low and high pressure sides coz youve introduced low pressure to the high pressure side of that outside fin, so now you end up getting an overall vector style type of drag (like when two trucks are next to each other going fast down the road ,the resulting lower pressure between them ,sucks the trucks together, like when you overtake a truck it feels like your getting sucked closer to it), so even tho theres some down sides to that foil design , what you get in return is a high lift fin , that is extremly reliable in high load situations ,even if you got the same area and put it into one larger fin , it would be slightly more efficient in some areas but then youd have trouble turning it, but your fin would turn on a dime with hold…
trade offs everywhere…
when i was reading your suggestions for testing the drag , id swear you were standing on the river bank in 95 …i did a number of tests just like you described ,with normal boards , not so much weight on them tho , i was duck taping 5 standard house bricks to the deck , my main aim of that test tho was testing the drag from different rockers , bottom contours and board sizes, i ended up testing every old board in the factory…now that i think about it some of my results could have been altered by the different fin configurations , but at the time fins werent my main concern…
im not sure if testing the fins using that method would work , as i found when surfing them they seemed to be most effective in turns , when the turbulent boundry layer is being forced against your fins at an angle, reducing the area for the boundry layer to hit is why i think they work so well ,
if you towed them behind a boat your not getting any angle of attack, unless maybe you tie a second line to the plug and pulled the tail to make the board veer off then measure the load on that line???or both lines maybe??
intersting stuff about drag and the type of tests done on some of those links , blakestahs comment about what terry hicks estimated the thickness of the boundry layer to be at 18mm stoked me …
coz in testing id done my estimates were 10 to 15 , but could go as extreme as 5 to 35 ,but the swim suit data reckons a minimum of at least 4mm and terry hicks said 18 ,and tom mentioned an inch, so my 10 to 15mm is right in the ball park…
after reading all that data on drag with boats and swim suits ,and some of the flat plane testing that had been done ,now i wonder if i wasted my time doing all those experiments when i coulda just got online…??
question??? how the hell do you guys find those links???
pretty impressive , it seems between us theres plenty of variety of strengths to make some progress in design…
i found some old pics from 88 just after i started my first bussiness and an old bussiness card from 87 which fell out of an old photo album…
if you look closely between the fins you can make out the speed fin logo…and the shape of the fin , but you cant see the fins in the photo coz of angle ,
ok thats me till the next post…
regards
BERT
Here’s an observation on boundary layer thickness and turbulence.
Years ago I was sailing down the eastern US coast on a Cherubini 44[http://www.cherubiniyachts.com/c44-c48.htm]. It was a moonless night after 2a. about 8 miles off the coast on North Carolina. I was standing by the main mast when I noticed a pod of Atlantic Bottle Nosed Dolphins swimming around and under the boat.
If you are following closely you might ask how could I see the dolphins swim under the boat? The water was very clear and looked black yet it contained microscopic phosphorescent plankton. They only lit up when they were disturbed. I could see every detail of the dolphins including the eyes as they swam 10 or more feet under water. They were perfectly outlined. It was a magical moment. They left very slight florescent trails. To my eye it didnt look like the layer of disturbed water was very thick even though the body of the animal was displacing quite a lot of water. It was not like some big blurry blob of light but a very detailed outline of the dolphin. I could see the vortices spinning off the fin tips: Every detail imaginable.
Now balance that observation with the shock wave bow displacement a boat produces and how dolphins can surf that invisible energy. Now add the observation of the traditional bow vs the current reverse bow with bulb.
Next look at this link [/urlhttp://www.cs.brown.edu/people/jfh/personal_other/boats/FAQ/node16.html]
BTW the C44 has a Scheel Keel which is bulbed and winged and predates all other winged keels. It puts a lot of weight where you want it while maintaining shallow draft which is important for Eastern sailboats. Probably not applicable to surfboards.
Anyway I just wanted to add some fuel to this thread. Anyone got a light?
Nice to see we have Cheyne Horan with us. Yo! (G’day mate!)
OK Gents,
I will be in Central America next week testing my modified FCS fins as it relates to this subject. There’s a solid swell forecasted for that week and hope to catch it going off…if the forecasts are accurate it should be headhigh to well overhead…aahoooo!
I modified another set of FCS AMs where the base length was reduced/refoiled from 4.7 to 3.5" long and about 0.7" high. Im planning to swap fins often between stock and modified…I’ll be riding a 6’6 EPS/Epoxy round tail travel board, 19" wide and 14" tail.
…cant wait to get out of this place!
mark spindler ,as im reading that story ,im thinking what an awsome experience …very lucky indeed …
meecrafty , ill be interested in your feedback,my asumption is you will lose a little hold , but i reckon you will be stoked with how much freeness it has plus more speed in the trims ,thats if you work your board…
well i was all ready to post the next part of the series on concave vector foils and assymetric leading adges …
but now im not so sure???
today i recieved the news that my fin experiments and design work have been frowned upon by mike and vince from futures fin systems???
to the point that they have banned me from purchasing there boxes.
they wont allow me to buy there boxes and put them in my boards ,
it seems the free thinkers and scientists in this world are once again being surpressed because of people trying to protect there commercial interests ,
it seems the search for refinement and knowledge are not really in futures best interests …have i found out to much already???would futures really be better off if i was silenced on this issue???
it seems that by shaving off the leading edge and scooping out the flat side ,ive somehow found myself encroaching on somebodies patent???
i might go patent all my rockers???
can you own a curve???
mike ,vince i really hope you guys will review your decision…im sure we can come to some arrangement…
tom ! any ideas im at a bit of a dead end here …
im not sure what would be the best way to go , do i have any rights???
regards
BERT
You know Vince told me he was going to get me copies of their patent applications. I haven’t seen them yet. I’m not sure what they’ve tried to patent. I’ve only heard rumor so far. The last time I did a search nothing came up. All that being said, you’re in Australia. They would have to sue you in Australia. Anybody can file a law suit. But, winning one is a whole different deal. Unfortunately, I’m all to familiar with being a target. At this point you’re not selling anything. You’re just discussing and testing theory in a public forum. Which could be used as a defense of documenting when a concept was initially developed. So, they probably don’t see it as in their best interest to make it easy for you to do research in this area. But, you can always use Red X (:
Bert Says, "today i recieved the news that my fin experiments and design work have been frowned upon by mike and vince from futures fin systems??? "
What kind of small minded possessive idiocy is this?
What can Mike and Vince be thinking about except the short term?
So Curtis Hasslegrave is the only foiler in the world!? I don’t think so.
If my words sound emotionally charged it’s because they are.
Surfing is about passion if you’re doing it right regardless of whether you’re riding on or working with surf-craft.
[*]noun: gradual improvement or growth or development [indent]Example: “Great progress in the arts”[/indent]
Some may argue that we aren’t involved in art, that this is all business. I’m from a different school of thought. I don’t think I’m alone.
Expanding on someone else’s ideas and refining design is called progress.
Do you think Edison’s ideas were all his own?
FYI, that’s how the internal combustion engine was developed. Work that stands near the cutting edge should be embraced not discouraged. Progress in business is always part and parcel of persuing the next new cutting edge not wacking it into piece and burying it where no one can see it.
Some get it, some don’t. Those that don’t want to live in some dark place where nothing happens except reviewing the balance in their ever dwindling bank account while the innovators surf in the real world of the present looking toward the waves of the future. Future may reconsider and start living up to their name. One never knows what’ll happen.
They aren’t protecting their commercial interests they are distroying them. If an innovator isn’t encouraged to make progress in the world of surfcraft why the hell would he want to build a board or foil a fin anyway. They may find their what they’ve done is just some dirty water they want to let run off and move on to that better wave that you’re riding, Bert.
You buy a Chevy but you can’t soup it up ~ Baloney! Next thing you know GM want to outlaw drag racing because of pattent interests ~ Yeah Right!
You make a fin box and nobody can make fins for it but you. Bullshit. The world will never be that small!
Good-on-ya, Bert
P.S. I wonder what Bill Bahne of Challenger Surfboards would have to say here. The fin box he created is clearly one of the most innovative things that has ever happened to surf-craft design. Consider how many variations of it are available now.
sounds like boycott time to me.
halycon! i so agree with the way you feel about it…and you worded it way better than i would of ,so everyone should get the point…
thanks for the offer tom…your system is solid and youve got the best foils of all the current systems , but unfortunatly they dont suit my contruction technique…
my boards have way more shear movement in them , so they bend further without breaking,the red x box ties the deck to the bottom stoping that shear,which in turn creates way more stress at the joins,plus i also use sl grade eps so it creates another potential place for water entry if it gets hammered around the foot area ,currently anything i set in has to be glased over to achieve the best quality ,futures suits glassing over real well ,i would also have to mould a thread into my fin bases…now nothings impossible ,but i do have a good system for moulding bases for futures…
im a bit confused , i rang mike ,he gave me the verbal ok to do my own thing with the fins ,he said something like "is that all you rang me for "“go for it dude” at one stage there was even talk off getting me to do some test models…
its seems i may have crossed the line when i made my own redesigned version of the vector fins and gave them to one of his teamriders(which were actually set up for fcs) his r&d rider said they were one of the best sets of fins hes ever used…
when i rang the rep for more boxes , that set of fins came up in conversation…
now i just sit and wait wondering when im gonna get a response from the top???
question???
dont futures make fins to fit fcs???
what about all the other fin companies ,who only make fins and not boxes???
or the companies who make interchangable products so there fins can fit other boxes???
is it right that one guy gets singled out and isnt allowed to buy the product???
even the sales rep was scratching his head…
come on mike/vince,ive got boards to build deadlines to meet ,this is causing me some anxiety ,even your team rider is waiting on a new board at the moment,what shall i tell him???
im putting in a pic , do these look like futures fins???
please consider carefully ,mike/vince,please see me as a valuable resource and not a threat…
regards
BERT
Bert, screw Future (they sold out to the Chinese anyway).
Your choices are: glass-ons; Red-X, or Lokbox.
Since you’ve ruled out Red-X give Lokbox a try. Bigger footprint than Futures; elliptical shape; slight rocker built in; fore & aft adjustable; glassed over; makes a FCS adaptor. & doesn’t use crappy plastic threads like FCS or Future!
Rob
BTW, nice fins. If you can put your custom fins in a Future base you can do the same for Lokbox.