Dang. Carl, I have some old model airplane wings you can have… have you ever tried fins with flaps?
I don’t know Mark, but I like your MVGs.
I put them on my Brewer(white MVG) retro fish and my Terry Chung(red MVG) minigun.
I think they feel different (a good different) especially under a regular thruster setup.
I rode the boards before and after and I could feel a bit of difference not a lot just a sense that things were smoother going rail to rail especially on the minigun which is a fast rounded pin with glass-ons. I think the shape has alot to do with it but I’m just a stupid design grem anyway compared to everyone here.
Hey and you’re right…
the less people know about a good thing the better for those of use willing to give these new things a try. It’s the 80-20 rule 80% failure 20% success but the 20% will give you more than the 80% in rewards. Let the skeptics talk stink or ridicule new ideas cause they get left behind in the long run anyway… Those are the guys hopelessly always chasing after ideas that have gone passe anyway. I’m sure alot of real old timers (60-70 yrs)are laughing at all this design discussion too…
As far as fat fins…
did mine I think back in '71-'72 out of foam. a hand foiled thick and stubbie little beast that I plopped right in the middle of a Lis-Style fish. Probably would’ve worked better on a pin-rounded pin though… I was inspired bythose surfer mag articles by Greenough and Hynson (remember his “Dolphin”?).
Don’t know if it was the mid-inducing drugs of those post flower child days or the fear of dying in the war, but we kind of didn’t give a sh"t about anything we did back then so experimentation in drugs, lifestyle, surf equipment etc was just a natural offset. Hell most of Morey’s far out article’s were probably written when he was high on hashish or acid on Kauai. We tried everything then and didn’t care if it worked or not… (reminds me of Chippy nowadays)…
But it seems like once we started to give a sht about it all and worry about who we were, what we did, how much money we made etc etc, all that “go for broke!” gusto just died as we pushed the envelope in other ways… Like getting ahead, beating the competition, being the best this or that… They used to say it was called growing up but I look at some of my peers and ancestors and wonder if that was all just western bllsh*t.
I’ve recently noticed though that even some young-uns like curren, slater, rasta and a ton of others have gotten to the point of pushing their new envelope so far that they’ve actually have gone beyond the whole thing again and have begun settling back into the old “i don’t give a sh*t” attitude of yesteryear and started experimenting again. I guess it helps to have their money but Curren hacksawing his fins in indo or riding his peterson fish in big surf, Slater riding his broken thruster as a twinner in monster Aussie surf, or Rasta doing the whole Dale mat surfing thing… Hell I remember doing the whole mat thing in the early 70’s using big garbage bags we’d inflate twist and ride at sandy’s and makapu’u just because it was something different to do.
Maybe it’s the crowds… Which is why we are so afraid to “waste” a session just playing around getting made fun of…
I don’t know…
Like Rich said technically it’s alot more sophisticated a discussion than fat versus thin.
Thin done right could be just as inventive and powerful…
but in my book and parked away in my fond memories…
fat fins are good stuff…
Sexy, fast, earthy…
kind of like a Gaugain versus an Escher
Seems hilarious that in half a century alot of us kind of (literally) grew into them…
kind of like growing into your shoes I guess…
This is why I love Sways…
Another great lunch time escape.
Is that a cheese and tomato finwich on the right? Those work. Thicker the better.
I’m going to spill. I have a cd by some former engineering students from a fine So. Cal. university. They did their senior thesis last year on hydrodynamics of surfboard fins. They used FU fins given them by the Bahnes. They tested in a water column. I would give more info, but the report is 77 pages and it clogs my hd which has filled up for some reason. I could probably open it in the Neptune, but that would constitute work and I’d have to bill someone namely myself. Kidding aside, it tool about 15 minutes to fully load last time I tried. Basically the results were simple enough, though the testing and research were rather excruciating. Their final conclusion was thicker was faster. They explained it as the result of lift. I’m sure that is way oversimplified. I will try and correct that deficiency later.
Now some people agree and some disagree how much of an effect lift has on a wing. But no one can deny that lift alone can pull a sailboat. Sails are flexible and can form near perfect foils. They have some advantages over wings in that they can decrease eddies by forming their own foil. They have some disadvantage from eddies that form around the mast. But the area of greatest lift is the area closest to the mast and along the boom. Which would be the leading edge of a fin. So anyway sails are very efficient foils. And they generate enough lift to pull a boat through water at speeds fast enough to have fun. How much lift is involved pulling or pushing a surfboard is probably not insignificant.
I talked to Greg Loehr earlier and he told me that he did extensive sailboard fin testing in the 80’s and that they found thin fins custom made from moulded aluminum only really worked well on a reach. And that they were fast. I didn’t do much sailboarding. My efforts were confined to a few months in early 1985. I had more deck time sailing. Interestingly I seem to recall on a reach you only need about 60% of your centerboard. Less center board…less fin… is there a parallel? I would expect so. Sure more centerboard will stabilize roll, which is something to watch out for on a reach, but on a reach you are generally after speed, so sometimes just the leading edge is enough. My sailing days are a long time ago so maybe I’m a little rusty on the facts. Perhaps someone else with more info on this subject can fill in my blanks or correct me if I’m wrong.
Also does this contradict the students findings? I’ll try and open their report later.
In answer to your question, I dont know, Carl, but things usually look like what they are, so, my final answer is, because those are airplane wings?
There seems to be something to be said for not loving a thing to death. Whenever I take anything or myself too seriously everything seems to either fall apart of blow up. Or both. Kinda like that scene in Tommy Boy. I can relate to that.
It’s much harder to put things back together afterwards, if it’s even at all possible, than to just chill, but how are we to know when to lighten up. By the time my brain gets the message it’s usually too late, the damage is done. Soon as the orders got realistic and it looked like a business was growing, pop fizzle. I don’t know what happened, but everything went wrong that could go wrong. Isn’t that a universal law somewhere by some Murphy dude? That cat was right. Well, for one thing I have a lot more respect for anyone who can keep anything going in this industry.
One of the things I was hoping for was exactly the kind of rambling storytelling you gave us. That hit the spot. I guess I’m looking for the stoke that fuels creativity. It was there once. It has been reported missing lately. It’s felt more like I was in a gang fight and I lost. It’s not that I havnt had ideas or that some of them aren’t reaching an audience. I have and they are. It’s more along the lines of where has the eureka gone? You brought some of that feeling back. Don’t know how you did it but thanks. Perhaps it was the honesty. In fact I’m sure of it.
You are probably noticing the same thing in Slater and Curren and co. Maybe it has felt to much like a business for them too. Heck Slater nearly plowed into me running out of the water after semi-final heat a couple months ago. Dam he was stoked. He friggin stared me down when I first got there a few hours earlier,too, while he was in the middle of the quarter final. I have video “proof”. I still wonder what that was about. I got a wierd feeling. Like he wanted to either talk or kick my ass. Or both.
Back to thick vs thin, I wonder if we could shift this thread to talking about chicks for a second and not skip a beat. I found that as I got a little older I liked them a little softer. Is that so wrong?
I wish Rich would take some more of the complication and mystery out of it, too. He has so many good ideas, but they could be better organized. Then we could see how they fit together much easier. It seems no matter who I talk fins with there comes a point where it seems like there are areas we really still just don’t get no matter how hard we try. And the harder we try the more complicated it becomes. So trying becomes self defeating. I think it’s still too early to declare that everything is known about fins, so we don’t have to ask any more questions. I just want to find the questions that lead to answers we can understand. Afterall, gotta have a motive of some kind. Mark
Hey Mark,
Well IMHO the boys from So. Cal are wrong.
I’ve read way too much naval architecture to swallow what they say as true. Lift and speed are two completely different things. Lift can create speed but I believe we’re talking about trim speed here. If you tacking a sailboard you in another world. We’re talking single fin surfboards right? If we’re not things have become too complicated to resolve anything.
Where you put the vertical cord in a fin determines how much lift you get out of it. If you create lift you create drag. You can’t get one without the other. If you create drag you loose speed in trim. You may create more speed as you turn but you can’t go as fast in a straight line. In the extreme what the boys from So. Cal. are saying is that if you pull a ball through the water on string and a pencil like foiled stick through the water the ball will create less drag. Well we all know how fast a ball stops when it hits the water.
Turbulence is created by a body going through the water. Bow wave – stern wave – they are part of this picture. Can believe the same sort of thing doesn’t happen around a body passing through the water subsurface. Thicker may be more effecient in some respects but when it come to how much the water has to change direction to get around an object a thinner one has to win.
When we start bringing up this like sails and assymetrical shapes we begin to wander away from the subject. The world of asymmetrical shapes incorporates all kinds of variables that extend the discussion only to muddle our approach toward real resolution and answers to what is being discussed, which is thick verses thin.
Have a look at the foil on one of Cheyne’s Star fins and the relative thickness and foil on the fin. The foil of this baby has to be in the picture when one considers what Ben Lexcen knew intuitively about fluid dynamics and what Cheyne can do on a single fin surfboard. Ride one sometime and tell me it doesn’t get through the water beautifully. Then put a thick single fin on you board of simplar depth and tell which one is faster. For the record this fin has it’s shape taken from and outline that was proven long ago to have lowest drag coeffienct of any wing shape. Sir Reginald Mitchell used it on his Marine Spitfire. Argueably the sweetest flying prop driven airplane every to mount the sky. Watch a movie of one in the airplane sometime. She is a magic! Have a look at the relative thickness of the wings. Not so strangely the outline also belongs to nature’s ultimate stealth flyer the barn owl.
Yes thicker produces more lift. Look at the thick foil on a biplane wing. It produces huge lift but the thing can’t make 200 mph. Look at the foil on a concord – mock 2+ relatively much thinner to my eye. Bonzers have a reputation for being fast. Put realatively thick side runners on a bonzer and see what happens. I assure you it won’t help with trim speed.
It seems to me that there is a cross over between what happens in the air and what happens in the water because of where a surfboard operates. On boards that surf in average surfing conditions thicker fins make a board more maneuverable and and give more lift but on a tow-in board going in excess of 30 knots it’s a whole other ball game.
Bulbous fins are too sensitive to directional change and in a survival situation this is dangerous. They wont let a board go any faster either IMHO.
Now there’s a guy that frequents this forum who I hope will show up here. He knows quite a bit about foils and has a huge amount of sailing experience. Hey T.O. where are you?
Mahalo, Rich
Rich,
I was angling for Tom too.
I was glad to see you didn’t let SURFER sneak that bad foil past you. Shame on them. In your face SURFER. That was 33 years ago? D’oh! Nobody told me. (My bad Homer impression. But that is what you get this time of night. 
I’ll open that report tomorrow.
(Eric if you are following this thread now or tomorrow would be a good time to jump in. Eric? Paging Eric.)
Later, Mark
Mark,
I had an in depth discussion about thick foiled fins with Phil in 1960 at the AJ surfboard shop, in La Jolla. Phil had brought several of his boards there to be glassed. He spent about an hour answering my questions, and explaining his design principles. To my surprise I found myself shaping next to him at Hobie’s five years later. My questions were centered on his thick foiled “reverse” fins. Phils focus was on maintaining laminar flow during abrubt changes in angle of attack across the “relative flow” of water on the fin. The impact on me was that it changed how I approached surfboard and fin design. I became more “scientific” about it and allowed the desired function to dictate the design. I have used thick foiled fins on several full guns, and have ridden them in big north shore surf including solid 25’ Waimea without any fin related problems. The most eye opening experience you can have is to have a really good board that you have ridden for a year or more, and have it “wired”, and then change to a thick foiled fin. I did that, and it blew my mind! My very good board suddenly became a “MagicBoard”. the first time I did a backside cutback the board “accellerated” and threw me off the tail. Or so my senses told me. The truth is that because of the thick foiled fin, and its’ laminar flow charecteristics, the board did not bleed off speed in the cutback turn as I was used to. Instead of leaning back to stay with the slowing board, I now had to lean forward to stay with the board going through turns.
EDIT: As an aside, would anyone be interested in a “Round Table” meeting in the So. Cal. area to talk story, talk fins, talk boards and such. It might stimulate something. A new path, a new insight?
Yeah, I had good experiences with thick fins when I had 'em, they were wood/foam/fiberglass combos on Parrish north shore semiguns. Worked unreal. I’ve also had terrible experiences on the thinnest fins available, that mirror Bert’s comments. And I agree, thick fins do seem to bring around the board better during the second half of big turns. Now I’ve recently experimented with a name-brand Hatchet fin which has a thicker foil near the tip on small waves, and it’s very loose and turns great, but I’ve come to believe I can noticeably feel the thicker foil slowing it down on fast, down-the-line type waves. I then took a standard fin and modified it to the same exact specs but without the thicker tip foil, and it seems to go faster but not turn as well. That seems to suggest to me a point of diminishing returns, where standard thickness fins may work best in most all around conditions, thicker fins in juicier bowlier conditions, and thinner foils for near straight barrel speed runs.
Hi Bill - you suggested a Round Table in SoCal… we do get together on occasion to talk story, shape, and/or glass. I’ll probably host another one sometime after the Kauai deal, but it would be great if you (or anyone) wanted to start something else in the meanwhile. Best to post it in the Events/Happenings/Hookups section…
I’ve found everyone to be interested in such events and lots of good stories & tips exchanged, boards compared, etc. All it takes is someone with a small amount of organization to get it going… pick a spot & time, Swaylockers will show up! Myself included…
aloha,
Keith
Tube,
First I have to say this is an excellent test idea you have thought up and done. I want to thank you for sharing your resuts here with me and everyone. That was a lot of good hard work. I hope you don’t mind too much if I apply a different set of criteria to your results? Maybe look at them from a differnt angle and apply a different light? I won’t shred you or your results that is not my motive. You found drag and I want to look at other areas where it may be found. You know, identify as many suspects as we can before we round them up.
Or to put it this way, may we look at some of the other variables as well?
Maybe it’s not the thickness that is totally responsible. That is a good starting point and you tested for it by changing templates and keeping the same relative foils. You made that suggestion and tested for it. Perhaps thickness alone may not be doing all the work to create the drag. Good. Maybe it’s other parts of the design. I agree and we can look at them.
My first impression looking at the fin: The first thing that catches my eye is that the hatchet fin has a lot of straight lines and squared off corners. Though water and air are both fluids not everything that works in one works as well in the other. Water doesn’t really attach well to straight lines. So maybe some of the drag you have narrowed down as associated with the hatchet is coming from the straight lines. That is my first thought.
Another suspect would be that huge trapezoidal “tip”. Fins and wings need to release the fluid off the tip and under load this release takes the form of a tip vortex. Tip vortices are a parasitic form of drag. And trying to create a vortex off that huge flat trailing edge is just asking for trouble. (I’m sure everyone knows these terms by now, but what I’m after is a logical progression of thought that requires I don’t skip steps or terms. I’m trying not to jump to conclusions. It’s boring and repititious, but necessary. Please bear with me.) A nice progressively narrowing tip with progressibvely smaller foil (a traditional tip) would give a cleaner release and create, therefore, a smaller tip vortex. There, too, the additional length is causing drag and maybe it’s not such a solid form to turn against, but it may be more fluid friendly and create less overall drag from all sources.
Then there is the sheer volume of the hatchet fin. Dragging that much volume through the water whether as a ball on a string or a finely tuned fin will have more drag than a smaller volume or a smaller ball. Maybe I can prevail on you to perform one more test, a volume test. Measure the volume of both fins with a displacement test and report back here with the results. That should tell us something. Okay?
It’s too early for final conclusions, but taking what we have into consideration the famous name brand hatchet seems to be a lot of unusual combinations from the book of not necessairily the best ideas. But I’m not condemning it. I’m just talking about outward appearance and comparing that against preliminary tests results and tradition. So far outward appearances tend to support and predict the test results. But there may be a specific type of situation or condition where it would be the best possible fin design combination. Maybe we should concentrate on thinking about when these design attributes will be needed?
Along the lines of your conclusion.
I like your three point suggestion. That is something to look at more closely as it is along the lines of where this thread can go. Good points. I’m going to break that out from the rest of the reply. I made a couple editing changes, but it’s all yours.
That seems to suggest to me a point of diminishing returns, where:
1.standard thickness fins may work best in most all around conditions (carving and pumping)
2.thicker fins in juicier bowlier conditions (top to bottom)
3.thinner foils for near straight barrel speed runs (steep and deep)
Pose a question here; how much is pumping an adaptation to equipment?
Proposition: What if less of a weight shift was required to create an equivalent increase in speed? I see this in some guys surfing. I wonlder how much of fin thickness is related to surfer weight? We already know fin size is related.
Quote:
A nice progressively narrowing tip with progressibvely smaller foil (a traditional tip) would give a cleaner release and create, therefore, a smaller tip vortex. There, too, the additional length is causing drag and maybe it’s not such a solid form to turn against, but it may be more fluid friendly and create less overall drag from all sources.
My experience has to agree with the above. A thick fin may be thick at the base but definitely should taper to the tip in a uniform manner. The thicker tips I tried did not feel as good or perform as good as tapered.
Quote:
Water doesn’t really attach well to straight lines.
That’s another reason I really liked the thicker foils, good attachment.
It’s also another reason I used straight edges for leading and trailing edges. Very clean entry and exit of water, not inducing any uneccessary drag, the specific angles of those edges transferring clean energy up to my feet and body weight positioning, not confused with curves.
I had a similar experience to Bill, and had to learn how to control myself and the speed, power and control available.
Thicker fins have, for any amount of lift, more drag than thinner fins. For any given lift, thin fins have a better lift:drag ratio.
Thicker fins have larger stall angles than thin fins.
Any board limited by stall angles will benefit from thicker fins. Any board on which you want little sensitivity at low angles of attack will benefit from thicker fins. These resonate with the benefits people claim from thicker fins…sliding through the water more easily (little lift at small angles of attack), pulling through the second half of a turn better (when the AOA is highest).
There is also the buoyancy factor…which I haven’t played with yet but some find significant…
There is also the stiffness factor which is usually on the side of thicker fins, and usually poorly controlled by people looking at thickness. And almost no one cares about, even some of the biggest fin companies. And its effects are enormous.
The SURFER article deals specifically with what happens at the highest angle of attack. They don’t mention that at smaller angles of attack, the thinner fin always provides more lift. Despite the heavy proponency of thicker fins, and the current buoyant RTM fins on the market, fins still have max widths close to 6% of chord length - definitely on the thin end of the scale. Millions of fins made in surfboard evolution…only the thinnest fins on the market…perhaps it is all about stiffness…
Maybe I’ll make some 12% fins after my current experiment is in testing…no time now…but my system is not limited by stall angle ever…so I bet I feel a loss of lift and not much else.
Okay, here are some shots of the foil I’m playing with this year. We just replaced the old keel that had longer cord lengths, wider girth and a shorter span with this one. We’ll see how the numbers compare after we finish dialing in the boat. On our own personal boat we have a much thicker girth like 20", the cord lengths are like 8’ at the root and 6’ at the bulb and the span is about 3’ shorter than this one. With the new keel I expect that we will be able to sail closer to the wind with greater effiency. i.e. the lift will generated by this keel at speed will allow us to sail closer to the wind. The new keel will also stall at a higher thershold. Meaning we have to keep the boat moving or it will start going side ways. So, back to thick versus thin.
Thick works better for bigger changes in angle of attack. Thin works better for smaller changes in angle of attack. The faster you go the smaller the changes in AOA.
Thick works better for bigger changes in angle of attack. Thin works better for smaller changes in angle of attack. The faster you go the smaller the changes in AOA.
BINGO!
Fin Foil Theory 101…
Combine that with Tubedogs conclusions and it comes down to surfing style and types of waves…so depending on wave conditions and style, one could have different sets of fins, thick, medium and thin to tune the board…nice! I’ve been delaying fin projects…time to pony up…
dam , why did i leave this thread till last , ran out of time …
killer stuff , everyone is right for there own needs …
who dertimines the needs of the masses??
ill be back ,tommorow …
mark , your on it , dont get disappointed if you cant keep the crowd focused and moving along orderly in a logical direction , answering questions with there own replies …
one quick question before i leave …
when do we go straight or when is there no angle of attack on a fin ???
even the poorest surfer is getting angles of attack that would have most flying instructors freaking …dont forget the drop ,even in trim there is angle of attack , thats why thruster longboards want to pull off the wave unless you weight your beach rail in a nose ride… my fastest board ever just standing on it with no pumping has the thickest fins , because just standing there , its still experiencing angle of attack as water comes up the face …
the arguments are right , but i dont think most crew realise just how much angle of attack we really need to tolerate …
ive said it all before , now i just wait …
blakestah , just do it …no more university talk … just go make a fat fin and report back …
your untested comments are wearing me down …
my own experiences are just like thailkils , got a good board put fat fins on it and it became magic …
drive from nothing , projection from a lean , thrust without a section , you wont find a formula for that in the text books , theres no substitute for experience …
believe it exists and you will start to see ,a closed mind sees no light …
mark , keep em focused im interested in where you want to take the subject , your vortex generaters are what the world needs if they cant see fat as faster , and i really want to try thick and a vortex combined , i can envision better still …
regards
BERT
Blakestah,
Getting closer and dicing it even smaller. Nice.
That original SURFER article old as it is has already generated about 33 times as many words as in the original article. I have not done an exact word count, but most posts look about the same size as the original article, so as a rough estimate I’m comfortable.
Stiffness is I suspect a big factor. I know Kelly is concerned with stiffness and we know how he surfs. Given the small size and relative thinness of today’s fins, wasting any energy to flex is probably going to show as a larger percentage than we might guess.
Thickness, lift, and drag. You are accurate that lift increases drag. And so it would seem that thicker higher lift generating fins would be slower. In a static water column test specifically. But who surfs in a water column? I’m not trying to be smart. I’m not smart. The water column test only measures one thing drag associated water flowing over the surface of the fin. I believe that this is a little different than a fin moving through water. So that is another test a drag test in a tank. I can’t do that. Testing the propulsive ability of a fin is another test I cant do. So I need to be methodical with what I can do.
Now put that fin on a board at an angle and surf it hard and the net loss in speed as reported above by several indicates that the net loss of speed through a turn is lower with the thicker fins. This is a crucial factor. Total energy lost over the entire course of the wave or ride. Once speed is lost you need to expend a great deal more energy pumping or by finding it on the wave face somehow and doing some positioning to regain it. More energy lost. Good luck if you are out in the flats. NOt so much a problm in smal surf, but watching clips of the guys in Billabongs XXL indicates to me that these guys might spend a lot more time figuring out how to gain speed to get out of the flats in front of those waves.
So, for now which fin recovers faster, the thick or the thin?
Which gets us out of the flats thick or thin?
Roundhouse cutback?
I’m begining to wonder if we can break it down by maneuver?
Take each maneuver and specify preferred type of foil.
From there maybe we can figure out what part of the fin is specifically involved in each part of the turn. That might be a good thing to konw.
Quote:
blakestah , just do it …no more university talk … just go make a fat fin and report back …
your untested comments are wearing me down …
…
Ouch…
I’ve already done fin thickness series from 5 to 7.5% thickness relative to chord length, and I got a result which I reported here. Thinner actually went a bit better. I have strong doubts I will find 12% better than 5 or 7.5% when I already find 5% better than 7.5%. But you have to control for stiffness if you go any narrower than 6% in glass.
…the rotating fin system relieves AOA, it shifts you to a need for thinner fins than antiquated systems in which fins do not move. Now, I would be REALLY interested if anyone had tried thicker fins in a rotating fin system and found them to work better…
I’m off to finish installing my RFS thruster boxes, about the size and weight of 2 FCS plugs, but crappy time of year for surf so don’t expect any feedback for a month or two. Fat fins might be next if I think enough of them to prioritize them…
Bert,
I noticed you posted a comparison of one of our original X-series fins for root cord comparison. How do you like the Next Generation Fins I sent you?
I agree, this is one of the great fin threads. In the past I had a hard time making sense of it all (just getting past the vocabulary is difficult enough), but I feel that I’m starting to understand some of the basics. I just want to check if I correctly understand what Cord Length means - The length of the fin along it fattest point.