i did a search and found lots of info on setups containing 1 to 5 fins. i couldnt find anything that describes how individual fin characteristics affect performance.
this is what ive gathered from general observation and discussion.
fin base: wider base = more drive
fin height: used to manipulate fin area
area: compensates for rider weight/wave power
tip area: more tip area = stiffer ride, less tip area = looser ride
rake: more rake = stiffer ride, less rake = looser ride
this is just to get people started. there is a good chance some of the above is inaccurate. ive also made some sweeping generalizations here.
how do double foiled fins change these characteristics?
how does flex manipulate these characteristics.
how do the other more subtle characteristics of fins affect their performance.
i guess its ironic that the short attention span thread is getting so much love…i know there are some fin freaks out there…doesnt this warrant any attention?
How about one question at a time. No one wants to have to write a book on the whole subject of fins. Besides, there are numerous threads addressing many of the points you raise. What is of the single GREATEST concern to you? That is the question you should be asking.
"how do double foiled fins change these characteristics? "
Foiled inner surfaces can vary greatly. You can have 50/50 convex down to 80/20 convex or even throw concave in there. The most obvious difference of inside foiled side fins as apposed to flat inside surfaces is that the flow across the leading edge is less turbulent and allows the rest of the foil to work more efficiently. The closer to symetrical the double foiled fins are the less pressure differential you’ll get for a given foil area (i.e. less lift in the direction of pulling your rail into the wave). 80/20 convex fins appear to be very efficient relative to flat sided fins at higher flow rates. But, flat sided fins or concave fins have better lateral resistance at low flow rates and give you more to push off of (or thrust out of the hole). The problem with concave fins is at higher flow rates they set up trailing edge trubulence.
“how does flex manipulate these characteristics.”
Vertical flex gives up energy and efficiency. Lateral flex allows the tip to conform to the flow of water and hence more efficient at keeping drag down and can loosen up a fin in tight turns.
"how do the other more subtle characteristics of fins affect their performance. "
Fuller foils with max girth forward allow for greater changes in angle of attack while maintaining efficient flow at low and medium flow rates. Finer foils with max girth further aft minimze drag at higher flow rates and tighter range of AOA.
Combining these features to max the efficiency of your foils for any given set of wave conditions is the next holy grail of board design.
my single GREATEST concern (to me) is understanding how fins work…im not really looking for an answer to one question, but trying to gain some understanding through discussion…is that allowed here???
i would be very interested in reading any threads that you know of that discuss fins themselves, ive searched…but to no avail.
I can’t believe that sucker went to 17 pages, it was on the front at Sways for months…
And, even by sways standards, that is only the tip of the iceberg here. There are dozens and dozens of gems about fins in other threads…not that it is a closed topic, but most of those who’ve thought a lot about fins have said a lot already, digest it and come back with questions…
You may be a non-curmudgeon since 1978, but you are a smart ass since 4:15 pm today. You DO need to refine your skill in searching the archives. The info is there. The advice in my first post of this thread was to help you, so get the chip off your shoulder. If straight talk upsets you, then this forum may not be the place for you. There is a wealth of information to be mined here, but you have to do some digging yourself. Don’t expect others to do the digging for you, or to spoon feed it to you. Much of the information shared here, has taken people years of effort and study to refine and understand. And it has taken some effort on their part to obtain the knowledge that you now expect to be provided to you for the asking. I’m sure you are telling the truth when you say that you want to know what a fin really does and why. You are not alone in that quest.
When you look at the base of the fin the base cord line is from the leading edge tip to the trailing edge tip. A 50/50 convex fin has symetrical foils either side of the base cord line. An 80/20 has a foil on the outer side that has a max girth which is 80% of the total fin thickness and the inside surface has a max girth that is 20% of the total thickness. Concave is curve outward from the base cord line and concave is curved inward.
Thrailkill - im not expecting anyone to spoon feed me anything…im approaching this whole thing with maximum humility…if you possess this magical thread searching ability, perhaps you would care to share that instead of your self-righteous diatribe.
as a side note: im a member of many technical discussion forums, many from their beggining. ive noticed that at a certain point some people who have been around the forum for a while decide that its much more fun to rail on new users trying to get inspired and discuss things than just be helpfull or not comment at all. ive witnessed how the attitudes of people like you can lead to the decline of the forum. its an interesting phenomenon. it usually becomes a thread of its own at some point.
sorry if my search skills are below par…i vow to try to improve…
I totally understand Bill wanting to direct people into using the archives; because there is a wealth of knowledge in there to be mined. Those of us who have been here for a while know what’s in there and how much effort that has been expended developing it. But, I’ve also just come off a trade show and spent a day explaining the same stuff over and over. So, while my first inclination was to let the archives work. Giving a brief summary should entice snurl to delve further in the library of design that is Swaylock’s Archives
Per my prior comment, go back to my first post, read it without the chip on your shoulder. You WERE given more help than you seem to know. Read the words, they mean something. Since you cannot snatch the pebble from my hand, you do not get the further benefit of my wise council. Sorry, that would be my self-righteous, wise council.
I don’t think Bill is trying to hang shit on you, it’s just that the subject is very rich and complex. Too much to hope to cover in one thread. Read the thread Blakestah mentioned:
Now weigh up the arguments presented and note who posted them. You’ll find people like Halcyon, Blakestah,Tomatdaum, Lokbox, Bert Burger and a few others synthesising foil theory and fluid dynamic theory with real world experience. You’ll never hear this stuff from one mouth or read it anywhere in academia - Swayloc ks is recording stuff, individuals would never had been able dream up or experience in a lifetime of trying- its something that has never happened before in the history of the sport. Which is why people like Bill know just how valuable the stuff in the archives is. After you’ve read the above thread, go to the advanced search function and search for other posts by the names mentioned above, using key words like foil, camber, angle of attack, etc.
Snurl, lighten up. It takes time to write thoughtful responses to big questions. And, smart people here may have already answered the question before. Often the same question gets asked over and over.
Don’t just drop a bunch of questions and expect the whole crew to unload their wisdom. People respond if and when it suits them. You are not owed an answer. If you have an interesting question that hasn’t been worn out before, maybe some of the smart people here will bless you with an answer. If not, look somewhere else or go figure it out.
Welcome to sways. another way to search (if you haven’t tried yet) is to look at people’s previous posts. Look at the users that Pinhead mentioned. They pretty much have fin design/theory locked down. So just search for their previous posts and make sure to have nothing planned for the next few hours, grab a tasty beverage, some snacks, and read away. Sometimes I have to keep going back and re-reading old posts because some of the stuff goes over my head but I’ll have it sussed out a few months down the road.
ive been lurking and reading (and rereading) the threads on flex and composite construction and now im hooked! i think i have systematically read almost all posts by bert burger (not to say that i understand his intentionally cryptic messages) so now, after experimenting with different off the shelf fins for a while now i thought id try to understand what was actually happening. the thread blakestah posted is perfect, im loving it all. now that i have that to go from ive been going off on little tangents, finding the other tidbits people have posted. im not sure if ill ever have it all sussed out, but the journey is fun anyway.
I’ve had that thread bookmarked for a year. I think today is the day I’ll undertake it. I find fins to be one of the more confusing aspects of board building. The vocabulary always bogs me down. Just as I think that I’m starting to get a grasp on the subject something new gets introduced and I feel like I’m back at step one.
there are aspects that give you performance gains fast, and other aspects that offer less gain with perhaps more effort…law of dimishing returns
wrt thrusters, here are the quick gainfull aspects:
Setup: location, spread, toein, cant, etc
Template size/design: bigger, smaller, all fins symmetrical, bigger fronts v. rear, vice-versa, etc etc; keep it simple using medium rake designs - ie what’s on the market
3a. Fin Flex: all stiff, all soft, some stiff, some soft etc etc
3b. Foil design: very esoteric shit but you can break it down to thick vs medium vs thin; and if youre bored add pushed or pulled, sharp edges v rounded
when you figure those out, you’ll be very satisfied if not delighted and everything else will become trivial in comparison.
my current favorite setup: stiff TC redlines front, flexible AM rear
cheers
PS - as you read the archives, you’ll know who the gurus are…
Hey Bill - Howzit going? In the new guys deffence, the archives can be really un-user friendly. As someone else down the line pointed out, a good way to find info is to “find all posts by…” someone such as yourself, Tom, blackstah (sp?) etc. who know what they are talking about - cuz alot of posts mention fins in passing, and many a person would give up trying to sus it out. I know my spelling sucks, but our spell checker is not that easy to use either. Am I complaining too much??? Sorry.
New guy - fins… So much info. so many fixed fin systems, so many foils, such ever changing surf… keep up the quest.